Here's a pro tip I've been taught 50 years ago from a TV repair tech: If you have an open resistor you want to know its original value, just scrape a sharp knife over the length of the bad resistor, then measure from the center of the scraped free resistor body to both legs of the resistor. One side will read open, the other will read roughly the half of the original value.
Agreed I'm thinking sure these things are not designed to actually power LED's to their full potential advertised lifespan, but that resistor also should not have crapped out without a separate failure.
The thing I find with chopper and SMPS a is that once you fry something usually everything goes… That transistor zener circuit provides the DC supply to controller chip … I think the feedback diode is used as a flywheel and would be used to keep the chopper circuit running in the event of a brownout situation where the mains dips for a moment. Been a few years since I worked with Tamtec on their light engines and associated designs
This reminds me. Way back i saw an investigation in maintenance/repair actions. I forgot the exact number but in something like 30% (yes this high) of the cases that something needed to be repaired the technician made a mistake and by doing so caused an extra problem that needed to be fixed. The mistake could be something like slipping with a screwdriver/drill (and damaging something), put to much voltage on an input, made the wrong adjustment, connected the wrong wires, using the wrong tool, used the wrong procedure and so on. That's why i hate to bring my car to a garage..
I haven't finished the video yet, but when you measured the resistor at about 11:40 you were still in diode mode on the software in the top right... :)
I worked as a design engineer for Tamlite and they used a simple hold off circuit which disabled the Chopper circuit until the input rectified DC across the smoothing cap had reached something in the order of 90v DC to prevent the controller IC from chattering … that utilised a small NPN transistor and zener arrangement …. Just wondering if it’s something similar? Guess I should watch to the end before commenting hahah😀😀😀
They control output voltage. Once it gets above some value voltage on one of the pins of the controller IC gets above some threshold as well and the controller starts to skip its pulses. It has nothing to do with the circuit that powers the controller IC itself.
Good-on-ya Dave ! Can't believe you did that (lol). I thought the rule was, 'start big then work down'. A quick bit of math, and it was 210 ohm if the Zena was 5.1. My money is on the bjt going tits-up..
Well that's what I thought the colors might indicate as well. But wouldn't that be a lot more than 1W? Was trying to guesstimate the voltage expected across it, and it certainly looks like it was running hot, so R = ^2/ 1W ?? At 210 ohms, might have had 14-15 volts across it?
@@mikefochtman7164 Thats a good point, and 210 is not a common value. It is safe to assume the Tolerance band is gold. That said, we still have the question, 'what failed first ?'. The extensive "browning" of the resistor would suggest that it failed over time, be it seconds or weeks. Think I'll rewatch the vid. ;)
What's the point of that 180K in parallel with the transformer and diode, for the zener dropper wouldn't just the connection by the 180k be enough, what is the point of the transformer-diode bypass connection?
Yeah, lesson learned - don't be hurry when can't identify burnt-out component.. 👍 Thanks for video, because, even failure is educational! I have mains test socket with option switches to connect light bulbs in series with smps after repair or to connect unknown status mains devices.. Helps a lot to prevent full burnout. You still have other lamp to look, what this resistor value, actually, was. 😉
Joey Here. I'm Saying There's a shorted component on that board. I'd say after watching your entire vid. One of the diodes was shorted to cause the resistor to get hot. There's has to be.
'Abort, Retry, Fail?' was the phrase some wormdog scrawled next to the door of the Edit Universe project room. And when the new dataspinners started working, fabricating their worlds on the huge organic comp systems, we'd remind them: if you see this message, {always} choose 'Retry.' Bad'l Ron, Wakener Morgan Polysoft
I've found partially burned resistors like that one, and they are often showing a reasonable resistance value. I would have measured that mysterious resistor before replacing it
You could also hook up mains through 2x 60W bulbs in series (acting as current limiters) and use an isolation transformer + variac. This way you can slowly increase the AC voltage before letting out the magic smoke. I have a video on this here ruclips.net/video/_VV9mvuu--Q/видео.html
I'd figure with testing you'd always have a low current trip point for the AC input. I bought one of those kill-a-watt meters (off brand, NASHONE PM90) and it has a settable current/wattage limit where it clicks the relay off when it's exceeded.
@@gblargg The lamp method has the advantage that it is actually a current limiter, not just an overcurrent protection. Due to the PTC characteristic of the light bulbs it does become a (not very good, admittantly) constant current source. A higher inrush current draw just lets the lamps light up for a few seconds instead of tripping the protection instantly.
pulls out the twin head 500 watt halogen work lamp, also useable most type of basic electric heaters without fancy electronic controls. rows of bulbs you can switch to parallel. I've also used vacuum cleaners, and others high torque brushed motors.
@@gblargg relays response time is in tens of millisecs...too slow for today's SMPS works...not to forget current continues to flow till the contacts move to " open" , before the arcing is fully quenched...
I'm not totally convinced there wasn't something else going on to cause that resistor to overhead in the first place. Back in the day SMPSU repair kits were pretty common for TV and VCR power supplies and they often came with strict instructions to replace ALL the parts included in the kit even if the originals tested OK in static tests and they were very specific about that. Of course that could be because they'd likely been stressed by the original fault but not yet completely failed or it could be that they exhibit a fault condition but only under load for some reason and they were part of the original fault. Hard to tell for sure but even though a quick test of the zenner showed it to be OK it did look like it had got hot as well at the teardown part of the video, might have been conducted heat from the resistor but maybe not?
I am somewhat confused... He was saying red or black, and then gold and silver... I'm trying to understand which colors he was referring to at any given time... I came up with either 100 or 200ohms, with my guess on the colors I felt they were... How far off am I? *edit* I am just after the fire cooked the resistors. Have not finished the video.
I'm confused about why that even happened. It was basically OPEN with the old resistor there, so even a lower resistor here shouldn't have done that, surely?
and working finish nowhere i am dissapointed,, i do this for living like 12+year.. my lord.. is voltage divider.. obviously condensators is se to max 50V check that transistor max base input then try some obvious seting,, check max voltage of thjat zener and then sett right voltage divider,.. voala.. no magick smoke.. then you can bit chance resistance like 3-5% up.. from base.. to be sure termal profile will be more gentle.. you can also make it touchy by termosilicon to cooler.. but be carefull dont make this radiojammer.. and aslo.. change that trash caps for SO-COM hard dielectric one... is worthy...
Ever tried powering mystery things with a variac and a 20w light bulb in series? 330vdc in Australia. And it is flyback voltage back to the zener. This comment because i am OLD!
E.T. phone home! Edison says, bring me a drink! NI integration? I've been look'n @ that also! his next number? an impy-dance!! looks like my receiver on the TV! check the circuit under load then>new resistor...insulate those long legs....u need a bolometer!!
They all do that... About after a lightbulb's lifetime. Hoax. Still haven't understood why you did not measure the resistor in a still working converter? It would need modification anyway to not fail from same cause
Aishi caps; not nichi or ruby, but still far higher quality than I would have expected in such a unit. Also, please NEVER stop posting the videos where things go sideways!!! These are so important for lots of us to learn that mistakes happen, its not the end of the world, we learn something from it, and we move on. It also gives us a glimpse into the thought process leading up to the smoke, and the thought process AFTER the smoke. SUPER important!!
Given the position and job, it's probably toasted in the other ones, so reading the bands would be tricky at best. Measuring in circuit tho, that'd work.
One little trick for dealing with burnt resistors is to clip a probe to a knife, and to use the knife as a probe that can cut through the layer of laquer on the resistor right in the middle. With a bit of luck, you can still measure one half of the resistor, and then find an approximate value of it by doubling the measured value. If one half is open circuit(ish), try the other.
i like this idea better. thank you for bringing it up as it would not have occured to me otherwise. it seems worth it for the extra 1 step to try and costs nothing at all, with no risks. worst case you cannot always get the resistance value, then need to turn back to other methods. nothing lost
As I repair something connected directly to main power supply, I connect the device in series with an old good light bulb. The light bulb should be the same power as a device. In this case I would use 25W light bulb. If your device has short circuit or from some other reason consumes more then expected - you've simple got lighting bulb and no damage
More videos like this please!! It’s so reassuring to us amateur electronics engineers to know that the pros can make smoke as well as we do. Brought a smile to my face on a grey and rainy day in the north east of England.
I tried the same reair on a similar power source (electronic ballast i was using for a HV power supply) and it smoked the same way. I think there is another problem and that resistor is the first one to go. Once you replace it, something else gives off the magic smoke. Those damn things are un-repairable chinesium.
I'm guessing the resistor is probably around 100k minimum and it was a 15.6v zener; 15.6V zeners are very common on these types of supply because it allows operation of 12V nominal supplies with some headroom for shitty regulation. I'm guessing 100k because at completely un-dimmed level you want less than 1W dissipation, so 240V RMS - 15.6V is 224.4V, 224.4V is 50.355k ohm ((v*v)/p = r) but you gotta assume 100% duty cycle with a reasonable lifetime so you're not gonna run 50k, you're gonna run higher, probably 100k-200k. Looking at the resistor, the color bands were probably red-brown-yellow-brown for 210k
Come on, Dave -- slap an 18V Zener and a 20k resistor in that thing and give it another try! And yes, a full reverse engineering video would be most welcome.
The switching IC is probably toasted after his experiment. The switching IC is toasted, because the zener is toasted. He could measure the zener, if it's a short, there's a small chance the switching IC survived.
The root cause seems to be the loss of capacitance of the cap near the switcher IC. The resistor is toasted during continuous charging of this cap. Normally the IC will be powered by the Aux Winding after startup. Great fireworks👍
but this resistor is never disconnected from the high voltage, it will not heat up appreciably more if the cap is dead, and a bit if current is diverted off the zener into the pwm chip... I still don't get it.
@@victortitov1740 hmm maybe if the cap is shorted rather than a loss of capacitance? Then the resistor leg is 0.4-0.6V above around instead of the zener voltage. Or maybe the zener itself was shorted to begin with? hard to say.
@@eDoc2020 hmmm actually it depends on it's initial value, if it was 22k originally there would be ~37V over that and the zener because of the 180k. But you are right that's not enough to pop it, must have had close to the full rectified voltage across it somehow?
I think there is an error in your reverse-engineered schematic. That diode going off to the transformer is not connected to the primary coil, that would not make sense. Instead it is connected to another winding that has the other side connected to ground. The 180k is the startup resistor, after the switcher has started the voltage from the extra winding feeds the IC via that diode, the resistor you changed, and the zener to ground.
Dave you could have soldered in a variable resistor. and started high at then slowly reduced the value. until the circuit started booting and working again. then after finding the value replace the pot with a decent fixed value higher wattage resistor
@@felixcosty Most I've come across may have it in the datasheet / label, but they generally are meant for signals only. If you need ones that will survive, have a look for a rheostat that is pretty much the old fashioned equivalent of a dimmer or speed controller.
This is a really bad design. The resistor should be lifted away from the board to help heat dissipation. The capacitors are not only under the heat sink but also right next to the resistor. A timing device for planned obsolescence.. The resistor is part of the startup circuitry probably 47K or 100K
So many LED circuits are designed to fail quickly, either by cooking the driver or burning the LEDs. Light bulb companies don't want to let go of that nice income flow they've had since incandescents were top of the line. Look up Big Clive's video on the Dubai lamps that can't be bought outside one small gulf nation for how they SHOULD be built.
My logic would have been to check the PSU from the working light to get the correct value (Assuming the PSU is identical between the 2 lights seen in the other vid..) But I'm not good at electronics. :-P I wouldn't know how to diagnose like Dave. ^_^
I'd love to see you reverse engineer/fix this. I learn most of the videos where you follow through, particularly because as an electronics novice I often make things worse before I fix them... 😁
I think if the Zener diode fails to open everything else would be destroyed including the IC since you would have the high voltage going thru the Vbe of the BJT direct to the IC :), what is interesting is that they are using this method as a snubber.
Luv it! had a guy do a very similar thing at work after I said I would take the time to look into it, but he knew better and dropped a resistor in that he thought was right by just using the MK1 eyeball and poof let there be light and smoke ... A trap for old players (sorry couldn't help it lol). I wonder if it stings more knowing you had other lights in the house that you could have just took apart in situ and took a quick pic of the area you needed and then brought that back to the bench, no reverse engineering needed really if that was the case. Oh well least the smoke alarms didn't go off.
You've just got to try it sometimes, this shows the reality of repairing someone else's crap, excellent video Dave it's a shame we can't thumbs up more than 1. Thanks for showing it warts and all.
So how to discover the resistor value, when it is fried: take a knife and scrape the top layer of it. Open the resistive material inside. Grab the multimeter and measure resistance between the leg and 1/2 of the resistor. Multiply by 2. Done!
The Morse code is saying He's NO repairman 🤦♂🤦♂🤦♂🤦♂, give him a brush to sweep the floor ,You have failed your interview in our TV repair shop 😂😂😂😂😂😂😂😂😂😂😜😜
I am seeing a lot of led bulb drivers being mains reference now, basically a APFC circuit driving the leds, just to improve PF and they still get quite hot.
Ahhh, why didn't you measure the voltage across that resistor before adding it? You could guess the power absorbed in it based on the voltage measurement.
some manufacturers have this really nasty habit of scraping SMD codes off components of their designs. It's infuriating and screams 1-planned obsolescence and 2-exclusive servicing.
I remember replacing a bad 10W ceramic resistor in an old TV long ago. There must have been some other fault that shorted the resistor across mains because the new resistor exploded into ceramic fragments. Now that was one big and loud explosion! Usually resistors aren't designed to heat up that much, so a failed resistor likely means there's some other problem.
You knew that infinitely big value (open) allows protection to kick before something awful happens, so even without RE a safe play would be to start with a big value and lower it in some steps. Still a fun video.
I would really like to know how you go about reverse engineering a simple circuit like that to start with. If I try it's like trying to unravel a plate of spaghetti and I soon get lost with what goes where lol! Must be worth a vid?
Usually when I have a power source that does that, it gets replaced as a whole. Replacing one part of the unit that's been over heated and damaged is not worth it.
Here's a pro tip I've been taught 50 years ago from a TV repair tech: If you have an open resistor you want to know its original value, just scrape a sharp knife over the length of the bad resistor, then measure from the center of the scraped free resistor body to both legs of the resistor. One side will read open, the other will read roughly the half of the original value.
Wow thanks for the tip
Great tip, thanks!
Nice tip indeed! Thanks for your comment!
Brilliant
Not a bad idea but it won't always work because the heat could have affected the resistive material over more of the length than the open portion.
Usually replacing a burnt resistor it's not a good idea unless you have the root cause
Yes, yes and thrice YES.
Agreed I'm thinking sure these things are not designed to actually power LED's to their full potential advertised lifespan, but that resistor also should not have crapped out without a separate failure.
I have learnt that the hard way
The thing I find with chopper and SMPS a is that once you fry something usually everything goes…
That transistor zener circuit provides the DC supply to controller chip … I think the feedback diode is used as a flywheel and would be used to keep the chopper circuit running in the event of a brownout situation where the mains dips for a moment. Been a few years since I worked with Tamtec on their light engines and associated designs
This reminds me. Way back i saw an investigation in maintenance/repair actions. I forgot the exact number but in something like 30% (yes this high) of the cases that something needed to be repaired the technician made a mistake and by doing so caused an extra problem that needed to be fixed. The mistake could be something like slipping with a screwdriver/drill (and damaging something), put to much voltage on an input, made the wrong adjustment, connected the wrong wires, using the wrong tool, used the wrong procedure and so on. That's why i hate to bring my car to a garage..
I haven't finished the video yet, but when you measured the resistor at about 11:40 you were still in diode mode on the software in the top right... :)
I was so annoyed seeing that, and glad too as it is something I do myself a little too often =)
@@magnuslindgren9460 I have as well many times lol
That secondary probably produced around 20V p-p and the zener needs 1mA so the resistor was probably around 10k.
I worked as a design engineer for Tamlite and they used a simple hold off circuit which disabled the Chopper circuit until the input rectified DC across the smoothing cap had reached something in the order of 90v DC to prevent the controller IC from chattering … that utilised a small NPN transistor and zener arrangement …. Just wondering if it’s something similar?
Guess I should watch to the end before commenting hahah😀😀😀
They still control something on the primary side from secondary via that optocouple.
Feedback loop for regulation.
They control output voltage. Once it gets above some value voltage on one of the pins of the controller IC gets above some threshold as well and the controller starts to skip its pulses. It has nothing to do with the circuit that powers the controller IC itself.
Good-on-ya Dave ! Can't believe you did that (lol). I thought the rule was, 'start big then work down'. A quick bit of math, and it was 210 ohm if the Zena was 5.1. My money is on the bjt going tits-up..
Well that's what I thought the colors might indicate as well. But wouldn't that be a lot more than 1W? Was trying to guesstimate the voltage expected across it, and it certainly looks like it was running hot, so R = ^2/ 1W ?? At 210 ohms, might have had 14-15 volts across it?
@@mikefochtman7164 Thats a good point, and 210 is not a common value. It is safe to assume the Tolerance band is gold. That said, we still have the question, 'what failed first ?'. The extensive "browning" of the resistor would suggest that it failed over time, be it seconds or weeks. Think I'll rewatch the vid. ;)
"Start dissipating a few hundred watts, then work down" :D
This is the rule for a field technician. For RUclips technicians it's the other way around.
You could maybe have taken a couple resistors and apply power to them to see how the color bands change when they burn.
Those resistors which burst into flames look like they were fusible resistors. They probably were the input overcurrent protection.
Video idea - get a bunch of resistors with different values and see what colour the bands go after being cooked up a bit...
What's the point of that 180K in parallel with the transformer and diode, for the zener dropper wouldn't just the connection by the 180k be enough, what is the point of the transformer-diode bypass connection?
Yeah, lesson learned - don't be hurry when can't identify burnt-out component.. 👍
Thanks for video, because, even failure is educational!
I have mains test socket with option switches to connect light bulbs in series with smps after repair or to connect unknown status mains devices.. Helps a lot to prevent full burnout.
You still have other lamp to look, what this resistor value, actually, was. 😉
Hi and thanks from Thought Stream UK on Facebook
Joey Here. I'm Saying There's a shorted component on that board. I'd say after watching your entire vid. One of the diodes was shorted to cause the resistor to get hot. There's has to be.
Well, you managed to stop it from flashing ;-)
Its great that you intentionally sacrifice working equipment to replicate a cock-up and thus educate use Dave. Your my hero ...
Apparently the first band was actually red? Looked like red, black, and brown on camera, but I can't see it in person.
'Abort, Retry, Fail?' was the phrase some wormdog scrawled next to the door of the Edit Universe project room. And when the new dataspinners started working, fabricating their worlds on the huge organic comp systems, we'd remind them: if you see this message, {always} choose 'Retry.'
Bad'l Ron, Wakener
Morgan Polysoft
Could have opened one of your others to check the value? Keep um coming Dave, only good thing coming out of Australia these days.
I've found partially burned resistors like that one, and they are often showing a reasonable resistance value.
I would have measured that mysterious resistor before replacing it
11:14 It's goneski
Thanks Dave for the video.
You could also hook up mains through 2x 60W bulbs in series (acting as current limiters) and use an isolation transformer + variac. This way you can slowly increase the AC voltage before letting out the magic smoke.
I have a video on this here ruclips.net/video/_VV9mvuu--Q/видео.html
Added a link to the video mentioned.
I'd figure with testing you'd always have a low current trip point for the AC input. I bought one of those kill-a-watt meters (off brand, NASHONE PM90) and it has a settable current/wattage limit where it clicks the relay off when it's exceeded.
@@gblargg The lamp method has the advantage that it is actually a current limiter, not just an overcurrent protection. Due to the PTC characteristic of the light bulbs it does become a (not very good, admittantly) constant current source.
A higher inrush current draw just lets the lamps light up for a few seconds instead of tripping the protection instantly.
pulls out the twin head 500 watt halogen work lamp, also useable most type of basic electric heaters without fancy electronic controls. rows of bulbs you can switch to parallel.
I've also used vacuum cleaners, and others high torque brushed motors.
@@gblargg relays response time is in tens of millisecs...too slow for today's SMPS works...not to forget current continues to flow till the contacts move to
" open" , before the arcing is fully quenched...
A new Dave technical term for me: "snotted". Just love it ...
I'm not totally convinced there wasn't something else going on to cause that resistor to overhead in the first place. Back in the day SMPSU repair kits were pretty common for TV and VCR power supplies and they often came with strict instructions to replace ALL the parts included in the kit even if the originals tested OK in static tests and they were very specific about that. Of course that could be because they'd likely been stressed by the original fault but not yet completely failed or it could be that they exhibit a fault condition but only under load for some reason and they were part of the original fault. Hard to tell for sure but even though a quick test of the zenner showed it to be OK it did look like it had got hot as well at the teardown part of the video, might have been conducted heat from the resistor but maybe not?
Dave, the proper procedure for repairing dodgy Chinese devices is: open bin, throw device in bin, close bin, order better quality replacement.
Hello sir why didn’t you use AC filament bulb in series just for safety
I'd be checking any other oyster lights from the same batch before the fire :)
............ a few second later: now You have to replace 1000 of resistors :)
Noce, ive done some engineering work on those things.
I am somewhat confused... He was saying red or black, and then gold and silver... I'm trying to understand which colors he was referring to at any given time... I came up with either 100 or 200ohms, with my guess on the colors I felt they were...
How far off am I?
*edit*
I am just after the fire cooked the resistors. Have not finished the video.
W H A T ??? Nothing Else Seems Fried ????? Y I K E S !!!!! LOL......
I did not finish the video yet but looks like to me the bootstrap resistor for the IC. I was waiting to blowup with a 1 ohm resistor 😂
Доподлинно известно, что вся электронная техника работает на белом дыме. Как только дым выходит - техника перестает работать...
I'm confused about why that even happened. It was basically OPEN with the old resistor there, so even a lower resistor here shouldn't have done that, surely?
Open = infinite resistance, very different to a low value.
why didn't you just pull the power supply from one of the other lights and see what you should have used.
and working finish nowhere i am dissapointed,, i do this for living like 12+year.. my lord.. is voltage divider.. obviously condensators is se to max 50V check that transistor max base input then try some obvious seting,, check max voltage of thjat zener and then sett right voltage divider,.. voala.. no magick smoke.. then you can bit chance resistance like 3-5% up.. from base.. to be sure termal profile will be more gentle.. you can also make it touchy by termosilicon to cooler.. but be carefull dont make this radiojammer.. and aslo.. change that trash caps for SO-COM hard dielectric one... is worthy...
Ever tried powering mystery things with a variac and a 20w light bulb in series? 330vdc in Australia. And it is flyback voltage back to the zener. This comment because i am OLD!
It snotted itself !!!
Whenever I see flashing, I check the capacitors.
We here call it strobing.
I^2*r
With 10A through a 0.1 Ohm resistor you'd be dissipating 10W
Dave Fucks it!! This is GOLD!! lololol. Nice one Dave ;)
I reckon you were maybe looking at a resistor in the order of either hunderds or a couple of K. of ohms.
Oh nice! DaveCad got upgrade ;D
To quote my old long gone Grey Beard who was my mentor...
"Shit Happens"
NEXT!!
Wow miss the magic Smoke...He Lives in a Dumpster..lol
You got more at home, look at a other one!
red purple brown gold too me lol 27 ohms ish
It would be nice if he would open a new one and measure values, then put those value in this one and retest. Ron W4BIN
Dave, you've stolen my nike glasses 🤩
Adam Savage has a demerit badge about this ;c)
E.T. phone home! Edison says, bring me a drink! NI integration? I've been look'n @ that also! his next number? an impy-dance!! looks like my receiver on the TV! check the circuit under load then>new resistor...insulate those long legs....u need a bolometer!!
Yes she "comma gutsa" but thanks for sharing 😀 👍
Ol' Murphy
They all do that... About after a lightbulb's lifetime. Hoax.
Still haven't understood why you did not measure the resistor in a still working converter? It would need modification anyway to not fail from same cause
Come a gutser? What does this mean in English?
if you have more of those things in your ceiling, please check those to. you never know where your fire hazard is,
Aishi caps; not nichi or ruby, but still far higher quality than I would have expected in such a unit.
Also, please NEVER stop posting the videos where things go sideways!!! These are so important for lots of us to learn that mistakes happen, its not the end of the world, we learn something from it, and we move on. It also gives us a glimpse into the thought process leading up to the smoke, and the thought process AFTER the smoke. SUPER important!!
Yeah, I use the aishi caps I often find in fluorescent lights
Once I also found a psu with two of them for filters.
My goof is your gain..... totally agree! (Everybody learns something)
High voltage caps from Aishi are ok. They are commonly seen in LED drivers.
Open one of the other lights you have in your ceiling and check the value of the resistor
Right?!
Hey, we all make boneheaded moves from time to time. If only more were willing to share the oopsies too we'd all be better off.
@@matthewellisor5835 I give Dave credit for posting the video
I'm betting Dave didn't want to drive home to get it. Lesson learned...try to have a working item for comparison.
I know….. I was also screaming this at the screen too!! :)
Given the position and job, it's probably toasted in the other ones, so reading the bands would be tricky at best. Measuring in circuit tho, that'd work.
I learned something: When in doubt about the multiplier band, start with the largest resistance it might be, and work your way down.
We started with open resistor 😂😂
It would definitely have been a good idea
Depends on the circuit though, in some cases a higher value could be riskier. Better to draw out the schematic and get more information.
smokin!!!
Or open another oyster that hadn't fried
@@Agent24Electronics how could it be riskier?
One little trick for dealing with burnt resistors is to clip a probe to a knife, and to use the knife as a probe that can cut through the layer of laquer on the resistor right in the middle.
With a bit of luck, you can still measure one half of the resistor, and then find an approximate value of it by doubling the measured value. If one half is open circuit(ish), try the other.
i like this idea better. thank you for bringing it up as it would not have occured to me otherwise. it seems worth it for the extra 1 step to try and costs nothing at all, with no risks. worst case you cannot always get the resistance value, then need to turn back to other methods. nothing lost
Bingo.
nice trick! thanks!
or check datasheet for basic set :)) or ration calculation :)) is worthy is acurate no trick ..
As I repair something connected directly to main power supply, I connect the device in series with an old good light bulb. The light bulb should be the same power as a device. In this case I would use 25W light bulb. If your device has short circuit or from some other reason consumes more then expected - you've simple got lighting bulb and no damage
Yes, old mains repair trick.
Wow cool!
100 year old trick, still as good today as it was back then 😃
With SMPS Ive found the dim bulb trick not always works too good. It stops the Thing Under Test from burning, but rarely permits it to start
Would a variac have helped?
More videos like this please!! It’s so reassuring to us amateur electronics engineers to know that the pros can make smoke as well as we do. Brought a smile to my face on a grey and rainy day in the north east of England.
"pros"?
Ha!
I tried the same reair on a similar power source (electronic ballast i was using for a HV power supply) and it smoked the same way. I think there is another problem and that resistor is the first one to go. Once you replace it, something else gives off the magic smoke. Those damn things are un-repairable chinesium.
I'm guessing the resistor is probably around 100k minimum and it was a 15.6v zener;
15.6V zeners are very common on these types of supply because it allows operation of 12V nominal supplies with some headroom for shitty regulation.
I'm guessing 100k because at completely un-dimmed level you want less than 1W dissipation, so 240V RMS - 15.6V is 224.4V, 224.4V is 50.355k ohm ((v*v)/p = r) but you gotta assume 100% duty cycle with a reasonable lifetime so you're not gonna run 50k, you're gonna run higher, probably 100k-200k.
Looking at the resistor, the color bands were probably red-brown-yellow-brown for 210k
Probably a bit more than a 15v Zener; many controller chips don't startup until 16 volts.
Agree was thinking 48k min
value of input resistor:
black-black-black-black
good thing you got all on video
Oh, wow, unlisted video. I'm in the Matrix.
Many flyback control IC go to hiccup mode when they detect overcurrent/short-circuit condition, so fault can be easy on secondary side.
Come on, Dave -- slap an 18V Zener and a 20k resistor in that thing and give it another try! And yes, a full reverse engineering video would be most welcome.
Yes, lets see this baby repaired.
The switching IC is probably toasted after his experiment. The switching IC is toasted, because the zener is toasted. He could measure the zener, if it's a short, there's a small chance the switching IC survived.
7:01 That's an S, not a 5. There could have been some worries had that been a higher-voltage 2SC device than the 945.
Yes, noticed this on the edit but forgot to add the overlay.
Saw this too, as soon as I saw '945 on the second line I knew exactly which jellybean it was!
The root cause seems to be the loss of capacitance of the cap near the switcher IC. The resistor is toasted during continuous charging of this cap. Normally the IC will be powered by the Aux Winding after startup. Great fireworks👍
but this resistor is never disconnected from the high voltage, it will not heat up appreciably more if the cap is dead, and a bit if current is diverted off the zener into the pwm chip... I still don't get it.
@@victortitov1740 hmm maybe if the cap is shorted rather than a loss of capacitance? Then the resistor leg is 0.4-0.6V above around instead of the zener voltage. Or maybe the zener itself was shorted to begin with? hard to say.
@@funkyironman69 A shorted Zener wouldn't make it smoke; the Zener voltage is an order of magnitude less than the voltage across the resistor.
@@eDoc2020 Yeah good point, maybe the 180k went short then?
@@eDoc2020 hmmm actually it depends on it's initial value, if it was 22k originally there would be ~37V over that and the zener because of the 180k. But you are right that's not enough to pop it, must have had close to the full rectified voltage across it somehow?
Love that you took the time to reverse engineer it to show us exactly what happened!
Agreed! Repair videos like these are fantastic.
I think there is an error in your reverse-engineered schematic.
That diode going off to the transformer is not connected to the primary coil, that would not make sense.
Instead it is connected to another winding that has the other side connected to ground.
The 180k is the startup resistor, after the switcher has started the voltage from the extra winding feeds the IC via that diode, the resistor you changed, and the zener to ground.
It says "we've been trying to contact you about your cars extended warranty".
LoL
11:19 You are in the diode mode, Dave...
Dave you could have soldered in a variable resistor. and started high at then slowly reduced the value. until the circuit started booting and working again. then after finding the value replace the pot with a decent fixed value higher wattage resistor
Just wondering would a decade resister work instead of a variable resistor.
@@felixcosty As long as your decade box has 1W resistors. Most don't.
Most are not 1W and high voltage rated
@@EEVblog How can you tell what the variable resisters wattage is?
@@felixcosty Most I've come across may have it in the datasheet / label, but they generally are meant for signals only. If you need ones that will survive, have a look for a rheostat that is pretty much the old fashioned equivalent of a dimmer or speed controller.
"i guess its the wromg value!"
...his famous last words
This is a really bad design.
The resistor should be lifted away from the board to help heat dissipation.
The capacitors are not only under the heat sink but also right next to the resistor.
A timing device for planned obsolescence..
The resistor is part of the startup circuitry probably 47K or 100K
So many LED circuits are designed to fail quickly, either by cooking the driver or burning the LEDs. Light bulb companies don't want to let go of that nice income flow they've had since incandescents were top of the line. Look up Big Clive's video on the Dubai lamps that can't be bought outside one small gulf nation for how they SHOULD be built.
@@truckerallikatuk The situation with the Dubai lamps is despicable.
My logic would have been to check the PSU from the working light to get the correct value (Assuming the PSU is identical between the 2 lights seen in the other vid..)
But I'm not good at electronics. :-P I wouldn't know how to diagnose like Dave. ^_^
I'd love to see you reverse engineer/fix this. I learn most of the videos where you follow through, particularly because as an electronics novice I often make things worse before I fix them... 😁
YES !
I think if the Zener diode fails to open everything else would be destroyed including the IC since you would have the high voltage going thru the Vbe of the BJT direct to the IC :), what is interesting is that they are using this method as a snubber.
Zeners rarely fail open.. But the way they apparently recover energy is indeed very interesting. I'd be in favour of a full reverse engineering.
Luv it! had a guy do a very similar thing at work after I said I would take the time to look into it, but he knew better and dropped a resistor in that he thought was right by just using the MK1 eyeball and poof let there be light and smoke ... A trap for old players (sorry couldn't help it lol). I wonder if it stings more knowing you had other lights in the house that you could have just took apart in situ and took a quick pic of the area you needed and then brought that back to the bench, no reverse engineering needed really if that was the case. Oh well least the smoke alarms didn't go off.
Surely there is high-def video of you opening one of these in the past where you could get the resistor code from?
You've just got to try it sometimes, this shows the reality of repairing someone else's crap, excellent video Dave it's a shame we can't thumbs up more than 1. Thanks for showing it warts and all.
Wow, everything I asked for in the eevblog survey in a single video!! As always a great educational video
So how to discover the resistor value, when it is fried: take a knife and scrape the top layer of it. Open the resistive material inside. Grab the multimeter and measure resistance between the leg and 1/2 of the resistor. Multiply by 2. Done!
sometimes the coil has degraded and oxidized when exposed to such extreme heat.
@@martininm.t.r.a9887 yep, but not always! you still have a chance
I haven't tried this myself by I've read about it before.
Looking forward to Part 2 of repairing this unit :P
The Morse code is saying He's NO repairman 🤦♂🤦♂🤦♂🤦♂, give him a brush to sweep the floor ,You have failed your interview in our TV repair shop 😂😂😂😂😂😂😂😂😂😂😜😜
I am seeing a lot of led bulb drivers being mains reference now, basically a APFC circuit driving the leds, just to improve PF and they still get quite hot.
Ahhh, why didn't you measure the voltage across that resistor before adding it? You could guess the power absorbed in it based on the voltage measurement.
some manufacturers have this really nasty habit of scraping SMD codes off components of their designs. It's infuriating and screams 1-planned obsolescence and 2-exclusive servicing.
I remember replacing a bad 10W ceramic resistor in an old TV long ago. There must have been some other fault that shorted the resistor across mains because the new resistor exploded into ceramic fragments. Now that was one big and loud explosion! Usually resistors aren't designed to heat up that much, so a failed resistor likely means there's some other problem.
Next time i hiccup, i will look for a burned resistors in my body!) Thanks!
flashing translates to 4, 8, 15, 16, 23 and 42 and must be entered every 108 minutes.
At least until Jack shows up and everything goes sideways.
Why wouldn't you taken apart one of your working ballast and get the value off of that I assume you have more than one
Hi Dave, please get yourself a Cliff Quicktest like BigClive uses. Those live un-insulated alligator clips should only be used by ElectroBoom.
Maybe Dave does it this way in honour of Steve Irwin ;-)
You knew that infinitely big value (open) allows protection to kick before something awful happens, so even without RE a safe play would be to start with a big value and lower it in some steps.
Still a fun video.
I would really like to know how you go about reverse engineering a simple circuit like that to start with. If I try it's like trying to unravel a plate of spaghetti and I soon get lost with what goes where lol! Must be worth a vid?
ruclips.net/video/lJVrTV_BeGg/видео.html
Imagine a lamp that gives you bios codes like a computer when it fails...
Usually when I have a power source that does that, it gets replaced as a whole. Replacing one part of the unit that's been over heated and damaged is not worth it.