The isolation on that board isn't good enough for that keypad to be ever considered SELV, I'm sure Panasonic understood this and designed the keys to meet standards for mains potential insulation (i.e. some plastic/membrane buttons like any microwave)
@@Patchuchan Unlikely. The bulb will only illuminates after the microwave is turned on at which point the finger is probably away. Even at that, there will be a plastic membrane between the buttons and the actual front of the microwave which would provide isolation.
Just repaired my CT55JW microwave. The control board *does* have a mylar sheet in mine so damage limited to one board. It had a nice black burn mark on it. The broken pcb track was easy to spot. Bridged it with some wire and solder. Oven works fine and the bulb/turntable are working again. Swapped bulb for LED so will hopefully not have this issue again. Thanks for the inspiration. Saved me £250.
LOL it also goes the other way. I had a brain surgeon/electrical engineer ask me about and ingrown toenail. Actually a blood blister under the nail. Needle nose pliers heated up a sewing needle melted a hole thru the nail cooled it back down with the ice cube back to skiing the next morning.
Isn't it great when you have people throwing shit at you from all directions faster than you can fix it? I had a boss ask me to fix his treadmill at home for free, then when I said I didn't have time, the asshole buried me with crap at work and gave me a bad review! I left about a year later after having enough of his passive-agressive office-games bullshit.
Sad fact though is the display uses more power than the microwave itself, simply because the oven duty cycle is so low, while the display is powered all the time.
SeanBZA That may be the case if you only use it once a year and it lasts for around a thousand years! I can't imagine how an LCD display, although LED back lit, can ultimately use the same amount of energy as a 1000 Watt inverter and magnetron. Even a VFD would use very little power.
A day is 1440 minutes. If you use the microwave for 10 minutes per day, the average power is 7 watts from that. Soit is not that far off. And 10 minutes may be a lot for 'average use'.
I find the Panasonic Inverters are problematic on the 120v as well, and yes the bulbs seem to be the contributing cause. It’s a shame as the old school non inverter were quite reliable and wouldn’t die. Inverters not so much. Very poor circuit design. Good thinking on doing a preventative bulb swap. I may do that now...
Brilliant diagnosis Mike, I have the identical failure on my Panasonic mwave. NN-CF760M The bulb blew making a pop sound, Fuselink blown and arcing carbon on both boards. Replaced track fuselink and its still kaput ..... 3 years old, about the life of a bulb !! My LAST Panasonic ever... Thanks for enabling me to see why it failed, for the sake of a 10p piece of mylar sheet, £270 gone west...
When I was younger my parents microwave failed in the same manner; bulb burnt out, microwave stopped working. I changed the bulb and it still didn't work. Since then I have actually gotten a Bachelor's degree in Electrical Engineering, but my parents like to bother me about the microwave "I ruined". I have to show them this. I did nothing wrong.
Its a shame they didn't put a sheet of fireproof cardboard between the boards to separate the high voltage electronics from the microelectronics. it would have cost ooh, 3p? Im sure there's a number of scenarios where having a high voltage board that close to low voltage microcontrollers could end badly.
Nice analysis, Mike. The filament in those bulbs is really fragile and the door closes with an almighty clunk, so I bet this is a pretty common failure mode.
I've seen the dead-short arc failure mode on a reflector bulb too. Symptoms were a) loud bang b) tripped 10A circuit breaker c) blown 25 or 30A phase fuse (with all the funky effects that entails). Upon closer examination, the part of the bulb closest to the base was blackened, and the screw part had an arced hole the size of a couple of grains of rice. Thankfully nothing low-voltage near it. Thought I'd mention the incident for future reference as to exactly what kind of currents can flow momentarily in this sort of failure mode.
I have a Panasonic inverter combination microwave, as the bulb has already died I.m probably OK. Those inverter microwaves are not bottom of the range and you would expect something better for the price.
Panasonic will have the entire board as a spare part though, but you probably will find it is a good part of the cost of a new oven, worth giving them a call though. Got a similar Sharp convection microwave, but sadly the keypad that wore out ( rest of it is still absolutely spotless and working) is no longer a spare stocked. Should get it out and look on fleabay for a used one or a complete panel with working keys, or look at putting a separate non membrane ( probably a cheap keypad unit) in place of it, as all I need really is the digits and the enter/start button.
Hi Mike, SNAP!!!!!! My original Panasonic 'Delta Wave' microwave, died. A year previous it had the megatron replaced but what killed it was the clock IC. It powered the primary transformer which in turn powered the secondary. The brilliant electronic guy in Battlefield Road in Glasgow (Innen Electronic for any of your viewers) said Panasonic had used very specific components on the IC board and when contacted they said these were no longer (he told me the cost of these components was pennies but without the values, it was very difficult to rectify). The electronic guy said it was a real shame as this issue rendered the oven (which was otherwise perfectly serviceable), a scrap item. Many thanks for sharing your experience. Originally, AvE sent me over to your channel. Kindest regards. Joe.
Thank you. My microwave failed and it turned out to be exactly the faults you have shown in your video. You saved me loads of time and I went out and bought a new one.
Thanks Mike. My Panasonic Microwave (same model by the looks of it) has done exactly this. Big flash, tripped the circuit breaker in fuse box, checked blown globe, same pcb track blown and arced over to the other board. AUD$1200 microwave trashed in a microsecond. Very poor design. Thanks for the excellent analysis.
I have a LG microwave made 15+ years ago, its controls are a timer dial and a power selector dial. Never had any problem with it at all. Still works perfectly. Meanwhile my brother has gone through 6 or 7 digital microwave ovens in the same time.
22 year old matsui with a 'clockwork' dial still in daily use here. still on it's original lightbulb too btw. for young readers matsui was the own label of one of our highstreet electrical retailers back in the oldendays :)
Sharp Carousel in my house with fully digital controls is still going strong 18 years later. The only reason I'm considering replacing it is the paint is peeling and the metal underneath is rusted
I just wanted to thank you Mike! I have a SIEMENS HF17056EU that started with a dead light bulb but ended up with something "strange" on the PCB I couldn't detect as all suspicious components checked out ok but the mw oven was not working right. Apparently I got lucky as I got only one PCB track fuse (marked PF on my PCB too) burned and nothing wrong on the LCD board and IC. I didn't know about these things and the copper track had evaporated without leaving any sign it was ever there. Simply bridged the 2 PF points back together and it worked great. This is a 10 year old model so I'll live with knowing I simply bridged the 2 together without calculating the right Amps rating needed. If something similar happens in 10 years time and my wire kills something else... oh well... Thanks again!!!
I have probably one of those Panasonic Inverter ovens, not sure about the model you have but clearly it is not the quality I would have expected. My unit is working fine but every now and then when I hit START, it would cut off itself like it's taking too much current and some protection trips. One time it blacked out and the clock reset itself as well. And it's less than a year old!
Check the transformer for any loose connection on the control panel, mine did the same everytime you did any movement and often upon pressing the start button. It ended up being a bad solder joint in the transformer itself where the primary winding connects to the pin. You can test this easily by removing the oven cover and wiggling the transformer and observing any result.
Mine does something similar. In my case it seems to be the turntable. Sometimes it gets into a state where the gears bind or something and it can't get moving, so it cuts out a second or so every time I hit start as that's a fault condition. Giving the turntable a shove seems to free it and it's fine again after that. Until the next time.
That's crazy! All the Inverter microwaves...and transformer microwaves I have taken apart have always had a plastic sheet between boards when they are close like that! It is insane what some manufactures will do to save a few bucks.
had the same thing happen with a toaster ( why does a toaster need a logic board) , mains arced over form the mains section and toasted the logic board. It was a small blessing that both sides of the toaster have there own logic.
Somebody threw away a microwave with similar fault next to my dorm. I never knew what killed the logic board, there was a glass fuse (for bulb) close to it blown to bits so now I know. Well, now I have esp8266-telnet-controlled microwave with single button in my dorm room
When your dump takes a while longer than expected because there are new duckfaced boobs on Facebook to ogle, you can reheat the cup noodles you put in before you went, just in time for the pants to come back on again.
Hi Mike, I had a Panasonic microwave some years ago which had the megaton replaced no problem. A few years after this event it stopped working again. The electronics guy I took it to in Glasgow diagnosed the clock IC. This clock/timer function then powers a primary transformer which then in turn powers the secondary transformer which powers the megaton. However, the conversation then went down hill when he told me the IC was a Panasonic special and no longer available. In summary, a 2 penny component rendered the machine scrap, what a bummer. Kindest regards. Joe. PS Found your channel through AVE.
Thinking of the time you spent on this hoping to get it works again. Because it was just a light bulb!! But no, this was hopeless because of a simple design fail. This should have been so simple to fix by yourself. I can't imagine your words when you realized you spend this time for nothing because of this reaction chain. Thank you for the learning. I will have a thought to this issue when making my next electronic design.
Acquired a clean Panasonic NN-ST477 (the all stainless one) dated '09 for a song from a charity shop earlier this week. The PCB configuration is the same and although the design is different there's a PCB track fuse. But on this one there's a drop-in clear polyester insulating sheet between them. So they clearly know about the problem and fitted an insulator, leaving me wondering if Mike's acquaintance's one had a manufacturing fault/omission. A warning: If you're taking one of the SS ones apart be very careful - it's got razor-sharp edges everywhere.
This was a fascinating short video! I'd happily watch mike repair other stuff! I remember that aussie repairing the one plasma TV. That was also very interesting. Any other youtubers that do this on a regular basis and could mike also do it more? :P I'd pay some to watch!
Thank you so much !!! I also have a Panasonic Inverter Microwave and - in full awareness now of what might happen - immediately ripped out the lightbulb, which btw is a custom one, not scewable. Now looking for a LED replacement. Guess i'll have to build a DIY one. Giantic thumbs up !!!!!! Now i think about replacing the bulb by a relay whitch then switches the bulb directly from mains power. Then worst case szenario would be the relay contacts could fail... On the other hand - a fast 150 mA fuse in series to the bulb wire could protect the Board as well...
@@AureliusR Actually i guess i missed that it was switched over a relay. I assumed some kind of thyristor. Looking at that it's very strange that the tracks switching a relay are getting destroyed when the load destroys the relais. How could that happen? Maybe someone has an explanation. It's the purpose of a relay to separate the load from the switching power - yet it failed to do so here. How? Anyway - i did replace the bulb with an LED that should last longer than a bulb, is brighter and will - if at all - hopefully once die more piecefully than a bulb.
We had a Sharp microwave that lasted at least 20 years (got free 2nd hand) the only problem was getting replacement bulbs for it. It used 2 120v bulbs in series but our local repair shop managed to get one , it ended up getting replaced by a 2nd hand sharp all in one which is ~10yrs old and although it has had a blown fuse in the plug (reason why acquired it, owner thought is was broken, replaced it and then realised it was the fuse) it still works like new. So sharp seem to make great microwaves.
I have a Panasonic oven that looks very similar, I'll disassemble it and add a mica sheet between the two boards (if it is built that way) and a 100mA fast blowing fuse for the lamp as well...
I had a glass fuse open on a 5V 200A power supply. Except it sputtered the glass envelope with fuse atoms. The power supply continued to work (but only without a load) because the fuse had several tens of ohms resistance. Replaced fuse with one which had a higher interrupt rating.
Exactly the same happened to my Panasonic microwave oven and I have to throw it in the bin. These circuit boards are very expensive to replace. Shame on those engineers who designed it
Wasserverschmutzung but if you had the inclination you could get them for the bad design "faults in manufacture" the warranty paperwork usually calls it... and limitation of warranty to one year is not legal. They're banking on nobody being bothered
Exactly, this is classic Sale of Goods Act territory, and with the analysis that Mike's done, you have all the proof you need that it was faulty from manufacture (by design, in fact).
Andrew Gillard i dont think thats faulty by design. it was a bad design yes, but they sold it like that and the warranty was over so if anything its your fault for buying from that brand. maybe if they was a page to add examples and have statistics of these events by brand, etc, people would stop buying from those who do it
If it allowed for mains voltage to go through a keypad when the bulb blew, makes you wonder how it passed it's electrical certficiation... You would think they would require some sort of mechanical isolation
I've had to repair my Panasonic as the small pcb-mount transformer on the control board had one of its pins detach from the primary mains winding due to repeated shock from opening and closing the oven door. I simply soldered the primary winding that was left to spare back to the pin and reinstalled the transformer. The control panel doesn't have any of the proximity issues to the mains circuitry as it did on yours, its more of a membrane keypad with a ribbon cable. I see yours uses an SMPS for the control circuitry and pushbutton switches... however the HV inverter SMPS looks identical. To activate the inverter circuit for some fun you simply feed it a PWM signal into the green plug, duty cycle = % power output.
Not really, no. The rest of the appliance is by no means cheap, sure, cost-optimized, but there's still a lot stuff in there that can't be cheap. It's probably just one of very few weak points of the design.
the mylar has probably been forgotten during manufacturing. These non changable lightbulbs (mostly lamps with fixed socket plus socket rivited in) are what is killing me. No chance for replacement without taking out the big drill.
Looks like that could be what happened - the '09 one I've just taken apart has a clear polyester insulation sheet between the two PCBs. If you look the PCB has another fuse track, bypassed by a wire link, in series with the one that's blown so they clearly expected in due course the bulb would blow and take out the fuse so they provided a spare.
My Panasonic was built in 1984 its still working just fine, just no numbers lighting up on the display panel. The dots and dashes light up and blink though.
The old incandescent bulbs always tripped out our lighting circuit when they blew, could usually see the arc flash very briefly before the house plunged into darkness.
definitely planned obsolescence. Panasonic are clever enough to make reliable microwaves if they want to; in their day they've made superb products. My Panasonic transformer microwave is 21 years old this year. It's never even had a bulb replaced. If they made them all like that, they'd reach market saturation. They found that out with the TV and VIdeo business.
This wouldn't pass the safety testing required for CE marking etc. It almost certainly compromised the safety barrier when the bulb popped and could have been a shock hazard if anyone had been touching the front panel at the time. Plasma during exposed fuse rupture is a known behaviour, so a Mylar insulator would have been required. It's a foreseeable outcome. The safety testing would have required fitting a temporary fuse in the protective earth, which would have blown here and failed the test. Panasonic lost their way on consumer products some years ago, if you check the reliability scores. They obviously became complacent. However, this seems to be a design issue, not just a manufacturing one, so things seem to be getting worse. Nowadays for things like microwaves and TVs I always go for Korean brands like Samsung - or failing that, German.
This looks like the microwave I have. Four years old and still the original bulb. I'm planning on replacing it soon so I might just let it commit hari-kari by lightbulb (provided it doesn't do it halfway through the cardboard pizza it's reheating). No doubt after posting this it'll either a) last forever or b) ruin my dinner the next time I use it
One thing I've noticed in my home appliance repairs as to microwave ovens. The controller chips work with different display panels dispite manufactures. The chip they use is probably generic to all last ten year ish microwave ovens. I've never had a light bulb trip a circuit breaker when it blows in the last 60 years.
Pretty common for tungsten table lamps to take out the 3A fuse in the BS1363 type plug when the bulb pops - I reckon it must have been the main reason for householders ever having to change a fuse
+Joseph Nicholas In the last couple of weeks I've puled two microwaves oyt of skips. Both were cheap BOB ones made by Midea and the control PCBs had multiple options selectable by snapping off small tags with loops of track on them.
I had a very similar thing recently. the lightbulb took out the psu in an industrial microwave. i thought "well thats weird, how are the ods". apparently not too bad :D
I hope you show this vid to the manufacturer As for the HV transformer, there's a few that have found ways to get the inverter working, usually with a constant 5v pulse to the interlock part, maybe charge pump, but i'm sure there's a way to find that output so it just needs power.
I just purchased a new microwave for $48. Given my one uses a large transformer I guess it will outlast a $480 inverter model. I like SMPS and inverter tech however I like the KISS principle and high MTBF more!
The same thing happened to my GE microwave--the bulb blew. When I took it apart, I found a vaporized track on the controller board. At the time, I didn't know about the bulb arcing and couldn't figure out why the track was gone!
Ive seen lots of products with plastic sheets between circuit boards. Having the mains board within arcing distance of the low voltage user interface board seems like a design flaw.
I was expecting a little bit longer of a chain of events that broke absolutely everything. But an overly-proprietary control board failing is pretty roadblocky on its own.
My mum's Panasonic micro has the same bulb, which I replaced recently and was annoyed enough that the bulb was not a standard hardware store part. I should go back in and check for and mitigate that potential issue. I think though, from an engineering perspective it's not unreasonable that this cascading failure mode wasn't anticipated, although it's perhaps a bit sloppy to have such close unprotected proximity between HV and controller circuits. But once the traces fuse due to the bulb arc that's the end of it anyway since jumpering the traces is useful for troubleshooting but not really a deliverable repair.
Nice bit of forensics there! What model of Panasonic Inverter oven was this? I have one of theirs (NN-CF778SBPQ) and although it doesn't have the same style of control panel as this one, I think I might check to see whether or not it has a similar lack of separation between control boards.
Do they already use IGBT in those microwave ovens, or it is still FET? Also, it is good to know that microwave ovens may have such goodies in them. Considering that they are close to 2KW, the ferrite high frequency core might be worth it for parts for building a TIG welder or an inverter...
Yes please! other than the normal sort of safety speech , I'd love to see the method of operation of the inverter, some numbers including operation frequency and IGBT gate trigger at different output powers.
Always the most annoying thing to happen just like the lightning spikes on Digi-boxes, TVs and WiFi/Lan hubs. At lease you will end up with some very nice parts out of the damaged item.
I got an immaculate Panasonic inverter microwave from a skip, the fault was the turntable motor was open circuit, a salvage part was fitted and it has worked fine for the last two years! I think I will fit a fuse for the bulb now....
Warranty period manufacturing really bites companies in the ass in Australia. We have a consumer law protecting the replacement rights of items to be "fit for purpose", i.e. significantly past the typical advertised one year warrantee.
This is what I'd expect from no name Chinese designed appliances but is not typical for Panasonic although they have also had their share of design fails. In general Asian engineers often do not understand potential failure modes beyond the few textbook examples they learn in college. Big companies that have been around for many years, like Panasonic, usually eventually learn from their mistakes while the short lived Chinese brands don't.
My Panasonic microwave is also a piece of trash, I had to fix the notorious door latch problems they suffer. The plastic that houses the light bulb degraded so quickly it actually crumbled into the microwave.
Built-in obsolescence at it's finest. One simple part causes the whole microwave to self destruct. Was many of the other parts still good like the inverter and fan? You could maybe get some nice arcs from that inverter. Maybe salvage parts off the boards as spares.
I suspect I just had the same thing happen to my microwave, except instead of the low voltage fuses blowing, the mains fuse blew, I'm going to replace it and see if it works, but I suspect that something else has gone as well, which might mean it's unrepairable... I can't imagine that immediately after the light globe going, the mains fuse would blow... there would have been a chain of events that followed similar to this video.
I have had a Panasonic inverter (and steamer) microwave oven get to a point where it would turn itself on and start running with no user input required... It stopped doing it after a while of having it unplugged when not in use, but still worrying.
This might explain what happened to my microwave (a Sharp that's an inverter type a few years old). It not only blew its own fuse (240V 10A ceramic fastblow) but tripped overcurrent switch on the circuit (and it was on an oven circuit so probably tripped from more than 10amp). I found out when I changed the microwave's fuse that globe was blown too, however in my case I found that microwave itself was fine, and it has been running fine since (without globe) for more than half its life.
Oh, thanks for leaving the comment .... your scenario sounds like mine, I'm hoping the fuse and the globe are the only thing I have to replace, fingers crossed! (both are open circuit but I'm hoping it's not a whole bunch of other electrical components), in my case my breaker didn't trip, just the fuse + light globe gone.
@@schr4nz personally I wouldn't replace the globe as then the issue is liable to happen again (it's the globe blowing that takes the whole thing down). The globe also isn't shielded well and in my case probably blew because spatters of liquid had got on it from food
@@schr4nz I should also mention (given the age of my original comment), that the microwave in question is *still* going, and as I recall it popped its globe+fuse at the 1 year mark, and I've had it 8 years total. So yeah, if I were you, I'd omit the globe (or find another way to stop the inductive charge being unleashed again when the globe inevitably pops again) trust me the light really isn't that important in a microwave. And given the thing (in my csse) popped a 20 amp 250 volt breaker... Yeah that's a design fault I'd rather not reproduce again.
It was old anyway... and solid-state electronic equipment, especially with VLSI, has a short and distinctly finite life. This microwave had no significant future left at the time of catastrophic failure.
Bad as this might sound... I kinda wrote you off as a total nutter with too many volts to play with :p But I knew you had skill... but im really rather impressed by this autopsy and diagnosis :D
I'd wager our host actually enjoys this kind of "hum-drum" electronics to 1) stay sharp in troubleshooting and 2) balance the intense focus needed to tear-down nuclear reactors, military satellites, DNA analyzers...
he name of this stuff escapes me at the moment, but that thin white plastic that is used to insulate things electrically, if they had put a sheet of that between the two back to back boards, would that have prevented this? Obviously the bulb and fuse blowing was going to happen, but the further damage may have been spared? Personally I want a socketed fuse or at the very least. a soldered in fuse, so I could somehow replace it if needed. I don't know about the average public, but I'm personally more than willing to pay a little more for a product for the factory to spend a little more on some serviceability items like that.
I bet the original design spec had a mylar sheet between the two boards, but it got costed out.
Removing it not only caused it to self destruct but if it happened while someone was using the keypad they could have gotten shocked.
That is very scary. I'm rather surprised that Panasonic would produce such a dangerous item, but I suppose every manufacturer has it's oops moments.
The isolation on that board isn't good enough for that keypad to be ever considered SELV, I'm sure Panasonic understood this and designed the keys to meet standards for mains potential insulation (i.e. some plastic/membrane buttons like any microwave)
@@Patchuchan Unlikely. The bulb will only illuminates after the microwave is turned on at which point the finger is probably away. Even at that, there will be a plastic membrane between the buttons and the actual front of the microwave which would provide isolation.
No. These are quality machines. I have one. The problem is in the design: no Mylar sheet.
>
Just repaired my CT55JW microwave. The control board *does* have a mylar sheet in mine so damage limited to one board. It had a nice black burn mark on it. The broken pcb track was easy to spot. Bridged it with some wire and solder. Oven works fine and the bulb/turntable are working again. Swapped bulb for LED so will hopefully not have this issue again. Thanks for the inspiration. Saved me £250.
Wait, what? You're a technician and your friends ask you to fix their broken appliances? I've never heard of that before.
I'm pretty sure brain surgeons get asked to look at friends ingrown toenails.
A friend of mine is a vascular surgeon and he actually operated one of our hamsters a few years back lol.
LOL it also goes the other way. I had a brain surgeon/electrical engineer ask me about and ingrown toenail. Actually a blood blister under the nail. Needle nose pliers heated up a sewing needle melted a hole thru the nail cooled it back down with the ice cube back to skiing the next morning.
It's a learning experience for Mike; this is his secret to being a know-all.
Isn't it great when you have people throwing shit at you from all directions faster than you can fix it? I had a boss ask me to fix his treadmill at home for free, then when I said I didn't have time, the asshole buried me with crap at work and gave me a bad review! I left about a year later after having enough of his passive-agressive office-games bullshit.
That was like watching CSI without the special effects
As a happy owner of an early Panny inverter, I am going to change the bulb and add an insulator just in case. Thanks for the heads-up.
Sad fact though is the display uses more power than the microwave itself, simply because the oven duty cycle is so low, while the display is powered all the time.
SeanBZA
That may be the case if you only use it once a year and it lasts for around a thousand years! I can't imagine how an LCD display, although LED back lit, can ultimately use the same amount of energy as a 1000 Watt inverter and magnetron. Even a VFD would use very little power.
A day is 1440 minutes. If you use the microwave for 10 minutes per day, the average power is 7 watts from that.
Soit is not that far off. And 10 minutes may be a lot for 'average use'.
I find the Panasonic Inverters are problematic on the 120v as well, and yes the bulbs seem to be the contributing cause. It’s a shame as the old school non inverter were quite reliable and wouldn’t die. Inverters not so much. Very poor circuit design. Good thinking on doing a preventative bulb swap. I may do that now...
I wonder if it was an I/O pin protection diode between the input and rails that failed in a shunted state with the flashover current.
Photonicinduction: Silly fucking lightbulbs!
"Don't last more than five minutes!" ;D
"They're Pants!"
read it in his voice.
For what it's worth, I really liked the one-take-here's-something-interesting-I-found form. Almost reminded me of a big clive video actually.
Brilliant diagnosis Mike, I have the identical failure on my Panasonic mwave. NN-CF760M
The bulb blew making a pop sound, Fuselink blown and arcing carbon on both boards. Replaced track fuselink and its still kaput ..... 3 years old, about the life of a bulb !! My LAST Panasonic ever...
Thanks for enabling me to see why it failed, for the sake of a 10p piece of mylar sheet, £270 gone west...
When I was younger my parents microwave failed in the same manner; bulb burnt out, microwave stopped working. I changed the bulb and it still didn't work. Since then I have actually gotten a Bachelor's degree in Electrical Engineering, but my parents like to bother me about the microwave "I ruined". I have to show them this. I did nothing wrong.
Nothing like people who don't let go of things, my dad still goes on about stuff I did 20 years ago!
Its a shame they didn't put a sheet of fireproof cardboard between the boards to separate the high voltage electronics from the microelectronics. it would have cost ooh, 3p? Im sure there's a number of scenarios where having a high voltage board that close to low voltage microcontrollers could end badly.
that 3p sheet of myler would have lost them the sail of a new microwave
You're assuming someone would buy a Panasonic again after it fails within 2 years. I wouldn't.
SALE
SAIL! ⛵
Nice analysis, Mike. The filament in those bulbs is really fragile and the door closes with an almighty clunk, so I bet this is a pretty common failure mode.
I've seen the dead-short arc failure mode on a reflector bulb too.
Symptoms were a) loud bang b) tripped 10A circuit breaker c) blown 25 or 30A phase fuse (with all the funky effects that entails).
Upon closer examination, the part of the bulb closest to the base was blackened, and the screw part had an arced hole the size of a couple of grains of rice.
Thankfully nothing low-voltage near it.
Thought I'd mention the incident for future reference as to exactly what kind of currents can flow momentarily in this sort of failure mode.
I have a Panasonic inverter combination microwave, as the bulb has already died I.m probably OK. Those inverter microwaves are not bottom of the range and you would expect something better for the price.
Mike, this was brilliant.
I have seen a similar fault on a dishwasher.
Worked at a Panasonic Service Centre . It was poor design & a common fault for years
I know the feeling of being everyones technical support. Can be quite tiersome. sometimes fun.
Panasonic will have the entire board as a spare part though, but you probably will find it is a good part of the cost of a new oven, worth giving them a call though.
Got a similar Sharp convection microwave, but sadly the keypad that wore out ( rest of it is still absolutely spotless and working) is no longer a spare stocked. Should get it out and look on fleabay for a used one or a complete panel with working keys, or look at putting a separate non membrane ( probably a cheap keypad unit) in place of it, as all I need really is the digits and the enter/start button.
Hi Mike, SNAP!!!!!! My original Panasonic 'Delta Wave' microwave, died. A year previous it had the megatron replaced but what killed it was the clock IC. It powered the primary transformer which in turn powered the secondary. The brilliant electronic guy in Battlefield Road in Glasgow (Innen Electronic for any of your viewers) said Panasonic had used very specific components on the IC board and when contacted they said these were no longer (he told me the cost of these components was pennies but without the values, it was very difficult to rectify). The electronic guy said it was a real shame as this issue rendered the oven (which was otherwise perfectly serviceable), a scrap item. Many thanks for sharing your experience. Originally, AvE sent me over to your channel. Kindest regards. Joe.
Thank you. My microwave failed and it turned out to be exactly the faults you have shown in your video. You saved me loads of time and I went out and bought a new one.
Thanks Mike. My Panasonic Microwave (same model by the looks of it) has done exactly this. Big flash, tripped the circuit breaker in fuse box, checked blown globe, same pcb track blown and arced over to the other board. AUD$1200 microwave trashed in a microsecond. Very poor design.
Thanks for the excellent analysis.
someone got a bonus for engineering this failure in. Very elegant :)
Looks almost as if it had proper fuses on the first ones. Bean counters changed that, what a lovely example of planned obsolescence.
I have a LG microwave made 15+ years ago, its controls are a timer dial and a power selector dial. Never had any problem with it at all. Still works perfectly. Meanwhile my brother has gone through 6 or 7 digital microwave ovens in the same time.
Built in obsolesence is a wonderful thing :(
22 year old matsui with a 'clockwork' dial still in daily use here. still on it's original lightbulb too btw.
for young readers matsui was the own label of one of our highstreet electrical retailers back in the oldendays :)
I have a 30 year old digital microwave. Still works, still its original bulb.
Sharp Carousel in my house with fully digital controls is still going strong 18 years later. The only reason I'm considering replacing it is the paint is peeling and the metal underneath is rusted
My 27 year old digital Sharp Carousel convection with sensor cook has never missed a beat. They can be made reliable.
Excellent forensic work. I will check if my Panasonic MW thing has a protection to avoid this issue. The bulb once blew, and I have not replaced it.
Oh dear, those naughty pixies have broken the confuser.
I just wanted to thank you Mike! I have a SIEMENS HF17056EU that started with a dead light bulb but ended up with something "strange" on the PCB I couldn't detect as all suspicious components checked out ok but the mw oven was not working right. Apparently I got lucky as I got only one PCB track fuse (marked PF on my PCB too) burned and nothing wrong on the LCD board and IC. I didn't know about these things and the copper track had evaporated without leaving any sign it was ever there. Simply bridged the 2 PF points back together and it worked great. This is a 10 year old model so I'll live with knowing I simply bridged the 2 together without calculating the right Amps rating needed. If something similar happens in 10 years time and my wire kills something else... oh well...
Thanks again!!!
what a catastrophic chain of events...
thank you for the post mortem
Nice work, Mike!
I have probably one of those Panasonic Inverter ovens, not sure about the model you have but clearly it is not the quality I would have expected. My unit is working fine but every now and then when I hit START, it would cut off itself like it's taking too much current and some protection trips. One time it blacked out and the clock reset itself as well. And it's less than a year old!
Check the transformer for any loose connection on the control panel, mine did the same everytime you did any movement and often upon pressing the start button. It ended up being a bad solder joint in the transformer itself where the primary winding connects to the pin. You can test this easily by removing the oven cover and wiggling the transformer and observing any result.
Mine does something similar. In my case it seems to be the turntable. Sometimes it gets into a state where the gears bind or something and it can't get moving, so it cuts out a second or so every time I hit start as that's a fault condition. Giving the turntable a shove seems to free it and it's fine again after that. Until the next time.
Less than a year old though, so getting it sorted under warranty would make more sense.
Not just planed obsolescence but brilliantly planned obsolescence !
That's crazy! All the Inverter microwaves...and transformer microwaves I have taken apart have always had a plastic sheet between boards when they are close like that! It is insane what some manufactures will do to save a few bucks.
had the same thing happen with a toaster ( why does a toaster need a logic board) , mains arced over form the mains section and toasted the logic board.
It was a small blessing that both sides of the toaster have there own logic.
Somebody threw away a microwave with similar fault next to my dorm. I never knew what killed the logic board, there was a glass fuse (for bulb) close to it blown to bits so now I know.
Well, now I have esp8266-telnet-controlled microwave with single button in my dorm room
That's cool but for what possible reason would you need to control a microwave without you being in the same room, in front of the microwave?
telnet? that's unsecure ;) you wouldn't want to get yor dinner hacked :P
When your dump takes a while longer than expected because there are new duckfaced boobs on Facebook to ogle, you can reheat the cup noodles you put in before you went, just in time for the pants to come back on again.
i am waiting for a bluetooth microwave, that notifis me when the food is ready , or lets me see/ add time
Actually the main purpose was to hack my roommate's dinner, I've gone too far when he nearly started to believe it was haunted.
Hi Mike, I had a Panasonic microwave some years ago which had the megaton replaced no problem. A few years after this event it stopped working again. The electronics guy I took it to in Glasgow diagnosed the clock IC. This clock/timer function then powers a primary transformer which then in turn powers the secondary transformer which powers the megaton. However, the conversation then went down hill when he told me the IC was a Panasonic special and no longer available. In summary, a 2 penny component rendered the machine scrap, what a bummer. Kindest regards. Joe. PS Found your channel through AVE.
That is heavy
I never would have guessed a bulb blowing could cause a short, I almost didn't click on the video because I thought it was clickbait!
Thinking of the time you spent on this hoping to get it works again. Because it was just a light bulb!!
But no, this was hopeless because of a simple design fail.
This should have been so simple to fix by yourself. I can't imagine your words when you realized you spend this time for nothing because of this reaction chain.
Thank you for the learning. I will have a thought to this issue when making my next electronic design.
Thoroughly enjoy vids like this, thanks Mike.
Acquired a clean Panasonic NN-ST477 (the all stainless one) dated '09 for a song from a charity shop earlier this week. The PCB configuration is the same and although the design is different there's a PCB track fuse. But on this one there's a drop-in clear polyester insulating sheet between them.
So they clearly know about the problem and fitted an insulator, leaving me wondering if Mike's acquaintance's one had a manufacturing fault/omission.
A warning: If you're taking one of the SS ones apart be very careful - it's got razor-sharp edges everywhere.
This was a fascinating short video! I'd happily watch mike repair other stuff! I remember that aussie repairing the one plasma TV. That was also very interesting. Any other youtubers that do this on a regular basis and could mike also do it more? :P I'd pay some to watch!
Thank you so much !!! I also have a Panasonic Inverter Microwave and - in full awareness now of what might happen - immediately ripped out the lightbulb, which btw is a custom one, not scewable. Now looking for a LED replacement. Guess i'll have to build a DIY one.
Giantic thumbs up !!!!!!
Now i think about replacing the bulb by a relay whitch then switches the bulb directly from mains power. Then worst case szenario would be the relay contacts could fail...
On the other hand - a fast 150 mA fuse in series to the bulb wire could protect the Board as well...
But there's already a relay switching the bulb on... why have a relay switching a relay?
@@AureliusR Actually i guess i missed that it was switched over a relay. I assumed some kind of thyristor. Looking at that it's very strange that the tracks switching a relay are getting destroyed when the load destroys the relais. How could that happen? Maybe someone has an explanation. It's the purpose of a relay to separate the load from the switching power - yet it failed to do so here. How?
Anyway - i did replace the bulb with an LED that should last longer than a bulb, is brighter and will - if at all - hopefully once die more piecefully than a bulb.
Ive got a steampunk microwave. Still works after 127 years. Never needed a new lightbulb.
We had a Sharp microwave that lasted at least 20 years (got free 2nd hand) the only problem was getting replacement bulbs for it. It used 2 120v bulbs in series but our local repair shop managed to get one , it ended up getting replaced by a 2nd hand sharp all in one which is ~10yrs old and although it has had a blown fuse in the plug (reason why acquired it, owner thought is was broken, replaced it and then realised it was the fuse) it still works like new.
So sharp seem to make great microwaves.
Nope, from your data we can conclude that Sharp made at least one good microwave. Look up "anecdote" from wikipedia.
I have a Panasonic oven that looks very similar, I'll disassemble it and add a mica sheet between the two boards (if it is built that way) and a 100mA fast blowing fuse for the lamp as well...
Nice bit of electronics detective work going on there
I had a glass fuse open on a 5V 200A power supply. Except it sputtered the glass envelope with fuse atoms. The power supply continued to work (but only without a load) because the fuse had several tens of ohms resistance. Replaced fuse with one which had a higher interrupt rating.
Exactly the same happened to my Panasonic microwave oven and I have to throw it in the bin. These circuit boards are very expensive to replace. Shame on those engineers who designed it
interesting detective work.well done.
that's quite nicely engineered to fail. light bulb lasts 2 years, warranty is gone, bulb fails and you have to buy new microwave.
My microwave is 30 years old, gets used every day and the original bulb still works.
Wasserverschmutzung but if you had the inclination you could get them for the bad design "faults in manufacture" the warranty paperwork usually calls it... and limitation of warranty to one year is not legal. They're banking on nobody being bothered
Exactly, this is classic Sale of Goods Act territory, and with the analysis that Mike's done, you have all the proof you need that it was faulty from manufacture (by design, in fact).
Andrew Gillard
i dont think thats faulty by design. it was a bad design yes, but they sold it like that and the warranty was over so if anything its your fault for buying from that brand.
maybe if they was a page to add examples and have statistics of these events by brand, etc, people would stop buying from those who do it
If it allowed for mains voltage to go through a keypad when the bulb blew, makes you wonder how it passed it's electrical certficiation... You would think they would require some sort of mechanical isolation
I've had to repair my Panasonic as the small pcb-mount transformer on the control board had one of its pins detach from the primary mains winding due to repeated shock from opening and closing the oven door. I simply soldered the primary winding that was left to spare back to the pin and reinstalled the transformer. The control panel doesn't have any of the proximity issues to the mains circuitry as it did on yours, its more of a membrane keypad with a ribbon cable. I see yours uses an SMPS for the control circuitry and pushbutton switches... however the HV inverter SMPS looks identical.
To activate the inverter circuit for some fun you simply feed it a PWM signal into the green plug, duty cycle = % power output.
built to a disposable price... *shakes head*
Not really, no. The rest of the appliance is by no means cheap, sure, cost-optimized, but there's still a lot stuff in there that can't be cheap. It's probably just one of very few weak points of the design.
the mylar has probably been forgotten during manufacturing.
These non changable lightbulbs (mostly lamps with fixed socket plus socket rivited in) are what is killing me. No chance for replacement without taking out the big drill.
Looks like that could be what happened - the '09 one I've just taken apart has a clear polyester insulation sheet between the two PCBs.
If you look the PCB has another fuse track, bypassed by a wire link, in series with the one that's blown so they clearly expected in due course the bulb would blow and take out the fuse so they provided a spare.
My Panasonic's 25 years old now still works fine.
My Panasonic was built in 1984 its still working just fine, just no numbers lighting up on the display panel. The dots and dashes light up and blink though.
how do you not have more subscribers? amazing channel.
Hm, very interesting - I never knew why they tripped the breakers .. thanks mike !
The old incandescent bulbs always tripped out our lighting circuit when they blew, could usually see the arc flash very briefly before the house plunged into darkness.
definitely planned obsolescence. Panasonic are clever enough to make reliable microwaves if they want to; in their day they've made superb products. My Panasonic transformer microwave is 21 years old this year. It's never even had a bulb replaced. If they made them all like that, they'd reach market saturation. They found that out with the TV and VIdeo business.
I amazed incandescent bulbs are still being used in micro's!
Incompetent design.
This wouldn't pass the safety testing required for CE marking etc. It almost certainly compromised the safety barrier when the bulb popped and could have been a shock hazard if anyone had been touching the front panel at the time. Plasma during exposed fuse rupture is a known behaviour, so a Mylar insulator would have been required. It's a foreseeable outcome. The safety testing would have required fitting a temporary fuse in the protective earth, which would have blown here and failed the test.
Panasonic lost their way on consumer products some years ago, if you check the reliability scores. They obviously became complacent. However, this seems to be a design issue, not just a manufacturing one, so things seem to be getting worse.
Nowadays for things like microwaves and TVs I always go for Korean brands like Samsung - or failing that, German.
This looks like the microwave I have. Four years old and still the original bulb. I'm planning on replacing it soon so I might just let it commit hari-kari by lightbulb (provided it doesn't do it halfway through the cardboard pizza it's reheating). No doubt after posting this it'll either a) last forever or b) ruin my dinner the next time I use it
What a bizarre failure mode.
Years ago quality light bulbs had an internal fuse for this reason. But nothing is quality nowadays, it’s all cheapened down to the bare minimum.
One thing I've noticed in my home appliance repairs as to microwave ovens. The controller chips work with different display panels dispite manufactures. The chip they use is probably generic to all last ten year ish microwave ovens. I've never had a light bulb trip a circuit breaker when it blows in the last 60 years.
Pretty common for tungsten table lamps to take out the 3A fuse in the BS1363 type plug when the bulb pops - I reckon it must have been the main reason for householders ever having to change a fuse
+Joseph Nicholas In the last couple of weeks I've puled two microwaves oyt of skips. Both were cheap BOB ones made by Midea and the control PCBs had multiple options selectable by snapping off small tags with loops of track on them.
It's what we refer to in the industry as a 'bastard' fault.
I had a very similar thing recently. the lightbulb took out the psu in an industrial microwave. i thought "well thats weird, how are the ods". apparently not too bad :D
I hope you show this vid to the manufacturer
As for the HV transformer, there's a few that have found ways to get the inverter working, usually with a constant 5v pulse to the interlock part, maybe charge pump, but i'm sure there's a way to find that output so it just needs power.
Very interesting as always Mike, thanks for sharing
the pcb track probably curled and touched, an oversight but one that needs a insulator between boards
I just purchased a new microwave for $48. Given my one uses a large transformer I guess it will outlast a $480 inverter model. I like SMPS and inverter tech however I like the KISS principle and high MTBF more!
The same thing happened to my GE microwave--the bulb blew. When I took it apart, I found a vaporized track on the controller board. At the time, I didn't know about the bulb arcing and couldn't figure out why the track was gone!
Sometimes I think I should come kneel at your door through rain and shine and sleet until you take me on as your padawan learner...
what will you do with the inverter?
i might have a idea
Ive seen lots of products with plastic sheets between circuit boards. Having the mains board within arcing distance of the low voltage user interface board seems like a design flaw.
I was expecting a little bit longer of a chain of events that broke absolutely everything. But an overly-proprietary control board failing is pretty roadblocky on its own.
Thanks for sharing! If I get one, first thing I will do is to put some isolation between boards or a proper cable inline fuse.
or change the bulb to a led replacement
My mum's Panasonic micro has the same bulb, which I replaced recently and was annoyed enough that the bulb was not a standard hardware store part. I should go back in and check for and mitigate that potential issue. I think though, from an engineering perspective it's not unreasonable that this cascading failure mode wasn't anticipated, although it's perhaps a bit sloppy to have such close unprotected proximity between HV and controller circuits. But once the traces fuse due to the bulb arc that's the end of it anyway since jumpering the traces is useful for troubleshooting but not really a deliverable repair.
Nice bit of forensics there! What model of Panasonic Inverter oven was this?
I have one of theirs (NN-CF778SBPQ) and although it doesn't have the same style of control panel as this one, I think I might check to see whether or not it has a similar lack of separation between control boards.
Do they already use IGBT in those microwave ovens, or it is still FET?
Also, it is good to know that microwave ovens may have such goodies in them. Considering that they are close to 2KW, the ferrite high frequency core might be worth it for parts for building a TIG welder or an inverter...
Yes please! other than the normal sort of safety speech , I'd love to see the method of operation of the inverter, some numbers including operation frequency and IGBT gate trigger at different output powers.
Interesting! This is probably what killed my parents' microwave. What a silly oversight.
Always the most annoying thing to happen just like the lightning spikes on Digi-boxes, TVs and WiFi/Lan hubs. At lease you will end up with some very nice parts out of the damaged item.
I got an immaculate Panasonic inverter microwave from a skip, the fault was the turntable motor was open circuit, a salvage part was fitted and it has worked fine for the last two years!
I think I will fit a fuse for the bulb now....
Sheet of plastic between those two boards would have saved this microwave. Shame.
the design is good for atleast 24 months, they said.
*It will work until the end of the warranty period, they said
Warranty period manufacturing really bites companies in the ass in Australia. We have a consumer law protecting the replacement rights of items to be "fit for purpose", i.e. significantly past the typical advertised one year warrantee.
Likewise in the UK and EU. Most people don't know it though!
It actually has a high likelihood of working for 10-20 years. Those bulbs often survive that long, and then they don't always fail short or arcing.
This is what I'd expect from no name Chinese designed appliances but is not typical for Panasonic although they have also had their share of design fails. In general Asian engineers often do not understand potential failure modes beyond the few textbook examples they learn in college. Big companies that have been around for many years, like Panasonic, usually eventually learn from their mistakes while the short lived Chinese brands don't.
My 1985 panasonic was built in Japan.
It was "Final Destination" time for the microwave :)
My Panasonic microwave is also a piece of trash, I had to fix the notorious door latch problems they suffer. The plastic that houses the light bulb degraded so quickly it actually crumbled into the microwave.
Built-in obsolescence at it's finest. One simple part causes the whole microwave to self destruct. Was many of the other parts still good like the inverter and fan? You could maybe get some nice arcs from that inverter. Maybe salvage parts off the boards as spares.
I suspect I just had the same thing happen to my microwave, except instead of the low voltage fuses blowing, the mains fuse blew, I'm going to replace it and see if it works, but I suspect that something else has gone as well, which might mean it's unrepairable... I can't imagine that immediately after the light globe going, the mains fuse would blow... there would have been a chain of events that followed similar to this video.
Fascinating. A resistive version of inductive fly back? I will be using TVS's across my lamps now. Thank you.
No, the lamp starts to conduct too much current, which vaporizes PCB tracks. Use a proper fuse in series with the lamp instead.
I have had a Panasonic inverter (and steamer) microwave oven get to a point where it would turn itself on and start running with no user input required... It stopped doing it after a while of having it unplugged when not in use, but still worrying.
Don't worry about the Panasonic - order an exorcism, as you obviously have a hungry poltergeist lurking in the house.
This might explain what happened to my microwave (a Sharp that's an inverter type a few years old). It not only blew its own fuse (240V 10A ceramic fastblow) but tripped overcurrent switch on the circuit (and it was on an oven circuit so probably tripped from more than 10amp).
I found out when I changed the microwave's fuse that globe was blown too, however in my case I found that microwave itself was fine, and it has been running fine since (without globe) for more than half its life.
Oh, thanks for leaving the comment .... your scenario sounds like mine, I'm hoping the fuse and the globe are the only thing I have to replace, fingers crossed! (both are open circuit but I'm hoping it's not a whole bunch of other electrical components), in my case my breaker didn't trip, just the fuse + light globe gone.
@@schr4nz personally I wouldn't replace the globe as then the issue is liable to happen again (it's the globe blowing that takes the whole thing down). The globe also isn't shielded well and in my case probably blew because spatters of liquid had got on it from food
@@schr4nz I should also mention (given the age of my original comment), that the microwave in question is *still* going, and as I recall it popped its globe+fuse at the 1 year mark, and I've had it 8 years total.
So yeah, if I were you, I'd omit the globe (or find another way to stop the inductive charge being unleashed again when the globe inevitably pops again) trust me the light really isn't that important in a microwave.
And given the thing (in my csse) popped a 20 amp 250 volt breaker... Yeah that's a design fault I'd rather not reproduce again.
It was old anyway... and solid-state electronic equipment, especially with VLSI, has a short and distinctly finite life. This microwave had no significant future left at the time of catastrophic failure.
moved plasma arc is often cause of mass damage in power supplies.
Bad as this might sound... I kinda wrote you off as a total nutter with too many volts to play with :p
But I knew you had skill... but im really rather impressed by this autopsy and diagnosis :D
Can you do a review on the fluke 287 or 289 Multimeter?
I'd wager our host actually enjoys this kind of "hum-drum" electronics to 1) stay sharp in troubleshooting and 2) balance the intense focus needed to tear-down nuclear reactors, military satellites, DNA analyzers...
remeber your cheap bullet time camera?? it would be interesting if you could make a real time synthetic aperture camera!
he name of this stuff escapes me at the moment, but that thin white plastic that is used to insulate things electrically, if they had put a sheet of that between the two back to back boards, would that have prevented this? Obviously the bulb and fuse blowing was going to happen, but the further damage may have been spared? Personally I want a socketed fuse or at the very least. a soldered in fuse, so I could somehow replace it if needed. I don't know about the average public, but I'm personally more than willing to pay a little more for a product for the factory to spend a little more on some serviceability items like that.
precisely its made in a disposable fashion - shame :( thank you for the dissection though :)
Ah, so that's why some bulbs have built-in fuse sections. TIL.