These are among my very favorite videos, where true skill and troubleshooting skills are put to the test. Random electronic, PCB failures. I love it. Well done!
Just to mention guys, I didn't have any high wattage resistors of the right value, so I used a couple of 51K and a 68K resistor in parallel (all 2W resistors) and this gave 17.5K which was close enough. The owner called me back the next day to say the aircon system was working perfectly. I think this is a large one which has four separate outlets (head units, whatever is the correct term) in different rooms
You remember the 4 circuits that you didn't understand the function of? They are communication modules, they communicate with the evaporator units. This board has 4 of them, but some boards have only 2, so the board supports only 2 units.
*** - I'm not understanding how 51k and 68k = 17.5k ?? Wouldn't that be 119k ?? How did you come up with that total number? Or to know the value of that open circuit resistor?
Some people just want to know the fix so they can get on with it and that's fine if you already have a lot of experience and understanding, personally I think it is great to see different peoples fault-finding methods as this is a skill in itself. Thanks for another great video.
I am impressed with your knowledge and use of logic and common sense. Your dad seams very knowledgable too! Your video’s have helped me a lot. Much appreciated.
Fantastic. I appreciate you. I’m pro hvac, setting up electronics workbench to repair these, heat pump defrost control boards, gas furnace control boards and 3 ph dc and ac motor control modules….as they are very expensive ($300-1600USD) to replace. The only videos I can find require me to know Hindi although I’m trying to understand by watching their methods. Very similar to yours! If you get a chance to do more hvac stuff, jump on it. Take care.
You could also have used a small file or Dremel type tool to file one side of the resistor down.. you should be able to see where the resistor coil is broken/burnt and measure each side and deduce the value.
I was going to suggest the very same thing but you beat me to it. I have done it many times on resistors that have blackened beyond recognition. It works well.
yes, This is something I practice myself too, I usually make a score in the middle and try to get a value from either leg to that and then double the reading you get.
I figured it out before you :), based on electrolytic rating, the zinner should be around 50 V. Zener current should be around 10mA. now 230-50/10exp-3= 18kOhms!
Keep in mind that environmental factors also come to play. I once had an MOV that was mounted close to an 800 degree heat source and that temperature melts solder connections. In this case, most of the solder dropped out of the 120VAC power connection and left the connection intermittent. I wouldn't expect this board to be mounted that close to a high temperature source, but that resistor could have created it's own source.
One thing that you didn’t mention that I couldn’t help noticing was all of those beautiful test points marked with voltages. So as soon as I could get this thing reasonably powered up, I would go to those test points to try and help narrow down any other faulty railson the board. It’s rare to have that kind of documentation on boards that I tend to get.
@kennymanchester I agree that is a good technique. If you watched the video all the way through, I did mention some of the ways I would have moved forward, including powering up the PCB. Purely by chance I had already found the fault before I got to that stage.
Excellent video sharing your thinking as you go ... you might treat yourself to one of those grinding pens to help get past the board coating which is indeed a real pain. 😀👍
Just an observation in the first 10 minutes; how nice is this cct board laid out? All of the components in straight lines, test point voltages marked and there is almost a schematic on the back.
This is god tier stuff. If only my school teachers made it this interesting 😂 probably wouldn't have skipped class nearly as much or got in half the trouble lol
Glad you have the wonderful weather. We had a tornado at 2:15 am (Central Florida), just north of my location. Not good weather but rather exciting, I guess (Sever Storm Spotter/Chaser). Thank you for your videos and taking the time to make the fantastic content! Take care!
just found this vid Richard, so using your expertise to try & fix my external General Air Con Unit problem of not communicating with the internal ones, wish me luck:-)
Wish you was my teacher in the 80s I was told my maths was bad but I learn from watching not reading so ended up doing DTP and data input because of my electronic teacher
Heya, always difficult to annalys a pcb if you don't know much about it, yeah oke you can do some basic measurements like you showed us. hopefully someone in the community knows this pcb that eould be nice. love to see these industrial repair video's it's quit differant
Good call breaking the unit down into 'modules'. The fact this particular resistor had its markings gone was also another clue ( usually a sign of heavy duty ) and then all the other stuff about how much it was likely dropping. I am curious tho, if it was an intermittent or continuous load that done for it. As you've hinted it is possibly down to a design/ specification issue, but it could also be something at the load end that is out of spec.
I've had some success figuring out damaged resistors like this by scraping off the coating and measuring as much of the carbon/metal film or whatever as possible. If you can measure from 1 leg to say half way and you get 10k , then you have an idea that it's probably in the 18-22K range. The resistance will be linear across the length of the resistor so it will scale linearly.
as it's the first component out of the live it sounds like a fuse resistor ... and it should be a hi wattage low resistance value ... about1 or 2 ohms and at lease about 2 watts ... so it acts like a fuse ... there are lots of these fuse resistors in circuits ... and also there's way that you can measure a blown resistor is that you can cut it in half and measure them ... one should definitely give a vale .. and that value is just about the half of the whole resistor ... this is a common way to measure blown resistors in repair .. you can even measure both half resistors and add up ... try it on a healthy resistor and se that it works ... these resistors have a simple structure and you can measure them cut in half... if length one half is double the length of the other half the resistance should be about twice the other half also. just try to make a clean cut. first try on another resistor and find the best way to cut clean.
I just went through a summer of highs in the 47C range here in AZ USA. If you can imagine we are a skinny state. I traveled to one of our eastern northern states recently and everyone was the size of a grizzly bear. Heat is good.
First of all, thank you for taking us along with your analysis of what the modular buildup of this board. Hmm, the DC part of the Bridge Rectifier looks a bit rusty, but it may also be the lighting playing tricks on me. Also the blue boxes at 5:49 look like capacitors to me, not relays, since they are marked C10 and C9 respectively(edit...Yes, you confirmed that later in the video), but your camera view might be out of whack with what you are describing here. What I would really like to know: *Why* the fusable 18K resistor failed; i.e. what the underlying issue or event is that caused it to fail.
Apparently this is a common fault on these PCBs as some others who are more familiar with them have mentioned. Thinking about it, one end of that resistor is connected directly to 220V AC, and the other end connects via a rectifier diode to a DC rail somewhere in the region of 'less than 100V'. So there is quite a high voltage across it and it clearly passes some current. I expect it was underrated by the circuit designer.
@@LearnElectronicsRepairIn that case it makes perfect sense to choose a 5 Watt resistor instead of the original one rated at approx. 3 Watt. Still, if it's intended as fusable, you might not want to pick a too high value here lest you overload more precious components further on in the circuit in the case of a failure.
@@LarixusSnydes Yeah I agree, it is a 18K resistor and a common failure on these boards, though I did not know that at the time. I actually ended up use three 2W resistors in parallel, two 51K and one 68K basically because that is what I had. That gave a total of 17.5K, 6 Watts. Though one could reasonably argue that the 68K resistor is passing less current than the 2x 51K so the actual max wattage will be a bit less than that.
Yeah it was a little bit darkened. Personally I thought it was not unusually so for a board that has power resistors so didn't initially go to it. Well done 🙂
Gentle use of a hot air gun is best for tricky boards with lots of copper etc., take it slow and heat it up gradually so everything heats up evenly and you don't burn stuff.
14:23 "what's this thing here" and "this big thing" -> reminds me of the movie "My Cousin Vinny" where Vinny cross examines the eye witness and asks "what are these big things, asking about bushes or trees. Also, so do you live in Maspalomas? Where are you originally from? What's it like to live in Maspalomas? Apparently it is often hot there, which makes sense, eh?
Well I considered part of faultfinding is seeing if anybody else has a fault with the item I'm working with. Hate looking up a video may or may not help me send you on a wild goose chase for it may actually be the problem you're helping. She usually never the problem I'm having which is why I need to start making more videos.
We can measure where AC and DC voltage from the 220 input to the end of the circuit with a multimeter, how can we find the fault by measuring the voltage from the electrical input to the end of the circuit. What are the parts used for?❤
I use a Sony HD camera mounted over the bench, similar to this one (I would have to check at the office to see the actual model) This is the one I am using to inspect the board www.ebay.es/itm/145331094527 I use a cheap 2K webcam mounted on one of the monitors for the 'face' insert - this one www.aliexpress.com/item/1005005305292588.html?af=ler2022 Another cheap 1080p webcam taped on to a flexible tripod originally meant for mobile phones for 'multimeter' insert - this one es.aliexpress.com/item/1005004711460364.html?af=ler2022 And a 1080P C Mount ELP camera with 5mm-50mm zoom lens on a desk tripod for side views www.aliexpress.com/item/1005004229884372.html?af=ler2022 I also use this THERMAL CAMERA (with the optional macro lens) Infiray P2 Pro s.click.aliexpress.com/e/_Dmuj4a7 amzn.to/457PgEb www.banggood.com/custlink/DDGPI7hRvU And I have a HDMI camera on my optical microscope, the Andonstar AD407 and a second PC to view webpages etc, plus another capture card for output from GPU or motherboards under repair. I record everything 'live' with picture-in-picture using OBS Studio (free) and I edit my videos with Davinci Resolve (free)
Will there be a video on all you need to know about relays? btw it seems that ads are back on sorin's channel i got 1 or 2 ads playing before the video starts but i don't see any on your videos it's quite strange
Curious why manufacturers which use PCBs, do not provide board/wiring diagrams, component I.D., and obvious test points so board evaluation can be done quickly? It would also seem that PCBs can be designed with "self check" circuitry which would indicate board function at a glance.
Hi, Any chance of fixing the circuit boards on a Miller Dynasty 200 DX, there is a forum on the web out of NZ called element14 from NZ, And from reading their forums a number of people, say that it is impossible to reverse engineer the Miller Dynasty 200 DX circuit boards. But when I saw your video, I thought you know your stuff and I reckon if anybody could do it, It would be you ! Any chance of laying their frustrations to rest and taking on a challenge no one has conquered ! A series with many parts and stages, explaining how to trouble shoot etc ... would be Awesome ! Please would you think about it !
Richard first very descriptive video.Have you made a decision on your teaching videos? Maybe if you can a good class i feel is one just explaining circuit board layout. Some of the symbology and how to know the difference between the higher voltage area and the lower voltage. I haven’t see videos explaining circuit board layout. Stay well. Artie. 👍
A great video! However you drive me crazy bending those components back-and-forth. A small angled dental mirror will get you the information you need behind these parts without risk of snapping off a pin and inducing another problem.
You had over 30c/26c at night in October? Wow, that´s awful. I too live in a house with bad(none) insulation and such temps as You have to bare would make my place a foundry, too. How fitting to repair an aircon, eh? I like to watch Your stuff, I have an old Radford TT100 I cannot figure out. Would You dare to take on a TT100? Kind Regards
Look at the Voltage rating of the zener diode. (Vz) Look at the wattage of the zener diode (Pz). Calculate the maximum current in the zener diode (wattage/voltage) Iz = Pz/Vz. This current (Iz) is the RMS current. The current in the zener might flow in pulses exceeding the RMS current (Iz). The same RMS current (Iz) flows through the resistor(Ir=Iz) (if you ignore the load parellel on the zener). The supply (240V) is a half sine. It's RMS voltage is 120V (240V/2). Substract the RMS voltage of 120V and the zener voltage(Vz). The result of this substraction is the RMS voltage over the resistor Vr. Now divide Vr by Ir (R=Vr/Ir). This is the resistor value you need. Take R 30% higher for safety. I assume the load parallel to the zener is around 1/10th of the load of the actual zener itself (which is typical).
Thanks Kris. It turned out to be an 18K resistor, either 3W or 4W though no one seems certain of the wattage. Your formula is good as you got somewhere in the ballpark with a lot of assumed values. 🙂
Zeners aren't resistors (well, duh!) They are rated for *average* power, from which you can calculate the average current rating. They aren't rated for RMS power because it makes no sense. The power in the resistor is indeed a function of the RMS current, however the resistor current and the zener current are not equal. The instantaneous resistor current is equal to the sum of the the instantaneous load current and the instantaneous zener current. If the load is resistive and that resistance is known, then its current will be equal to the zener voltage divided by that resistance. You simply can't ignore the load current in design of a zener regulator circuit. Matters are further complicated when capacitive filtering is used. If the capacitor is directly across the zener it will do nothing of value unless you allow the voltage to drop below the point where the zener is conducting. That means that when the instantaneous input voltage rises above the capacitor voltage the current through the resistor will have to charge the capacitor. That cam make the overall RMS resistor current higher than predicted by "rule of thumb" esitmates. The RMS value of a half-wave rectified sinusoid is not half the RMS value of the full sinewave, it half of the _peak_ value of the sinewave, taken over the full cycle period.
First of all, yes, I should have talked about average zener current. In typical zener design the load current is about 10 times smaller than the zener current. I am aware of that error. We're trying to get an idea of the range of the resistor. The capacitor just acts as an energy reservoir. It does not consume any active power. That is the reason why I only use RMS values. During normal operation the voltage over the cap is the zener voltage. The amplitude of a 240V AC signal is 240*sqrt(2) volt. To get the RMS of the half sine wave you've to divide this amplitude by (2*sqrt(2)) which gives you 120. The voltage over the resistor is actually not a half sine wave, it's more like a half sine wave cut off from below. And you would need to calculate some integrals to get he RMS voltage. I know I make an error here too. I know I cut many corners. If you want to have an more accurate estimate you can run a simulation in SPICE, using a load current of 10% of the zener current. @@d614gakadoug9
About the unknown resistor: could You take away the outer coat with a Dremel (I assume that´s a wire wound) and measure from the fault to the ends to add up the results? Could it be that rather simple? Well, this isn´t my idea, I stumbled upon it in here somewhere in time. I´d try- the part is already broken.
Expecting current limit sufficient to protect "sensitive" circuits by setting the current limit on a bench supply is folly! You will get current limiting ... eventually - after the output capacitors in the supply have sufficiently discharged. In the mean time you could get a current transient that could be tens of amperes even with a fairly small supply. If you must use this method, the leads from the supply should be kept short circuited until it is time to apply current to the thing being tested.
Fair comment, probably better to add an LM317 to the output of the bench PSU to set a current limit using that. Generally speaking though this method is fairly safe when testing relays in circuit as the applied voltage is only the same as the switching device would apply to the relay coil anyway. I don't recall anything ever being damaged when I've used this method in the past but of course there will always be exceptions.
@@LearnElectronicsRepair For lots of things there is no issue, but you can turn semiconductors into light emitters, even if they aren't intended to be, and LEDs into DEDs.
I'm late to this but your comment catches my eyes. What? Do you mean the engineer won't gave a spare board because he may be scare for the life of the board?😆
If you use the continuity tester, it would not be advisable to connect the - pole to ground, because the multimeter injects up to 5 volts and this can destroy components. Plaese measure the volts at the test terminals of your multimeter! Tip: Only use multimeters that inject 1 volt!
I have an Asus M2N32 sli motherboard that stopped posting. I tested all the voltages at the psu and all are good. When I plug in the 24 pin connector with the ATX 4 pin, nothing runs, but the standby led lights (on motherboard). If I unplug the 4 pin connector, everything runs but no post. All 4 pins on the connector socket show continuity to ground. Any ideas how to diagnose the component(s) causing this short to ground?
Why didn't the aircon tech just replace that resistor, they know what the common faults are but just want the margin they make by being a board swapper and not a technician. Most of them are clueless fraudsters.
I'd wish some aircon techs were board swappers. Nowadays quite a few aircon techs simply see the entire outdoor unit or indoor unit as the only parts in the system to be changed - the idea of a tech opening up either unit to do anything fault finding is simply not worth the time when a new replacement unit might only cost 400 euro.
Field techs dont fix board issues. For an AC unit the should be HVAC certified, at least thats how it is here in the US. So they would recharge or replace compressors, condensers, motors, the control board, and anything that can be repaired gets sent back to a manufacturing facility for rework and what cant get they probably have a contract with some company that handles E waste and then that company probably sells what can most likely has some value to salvage off it to grey markets in places like Mexico, or somewhere like Viet Nam for component stripping and salvage.
@@LearnElectronicsRepair Yeah i did watch the full video and knew about the resistor value but i wonder if there's a formula to use to get the value of an unknown resistor in a circuit especially the smd resistors are hard to know if they're burnt
When you use a multimeter in diode mode to see if there's a shorts on the capacitor rail, what reading should the multimeter give to indicate it's a short circuit?
Generally a short will read zero ohms or very close to that. However, once you find a 'short' in diode mode, make sure that you double check in resistance mode. Some voltage rails my have very low resistances when the circuit is operating normally and also if there are a large capacitors on a voltage rail it may look like you have a short for a couple of seconds while the capacitors start to charge, then the resistance reading will start to increase.
The black transformer at the end of the board is a current sense transformer with a full-wave bridge rectifier on the output. After the bridge will be a low-value loading resistor - likely in the range of a few ohms to 100 ohms or so. The switcher control IC is intended for use in a quasi-resonant circuit where a snubber is not required, hence none is shown on the typical ap circuit on the datasheet. Note the cap from the FET drain to ground. There is no evidence of such a cap on the PCB (typically would be a moderately large type with polypropylene or "better" dielectric. It looks to like the circuit on the PCB is a conventional flyback.
Thanks for confirming my suspicion that this is a current sense transformer. It looks like it connects (after the four diodes/bridge) to the black module on the right of the PCB below it. This has high and low voltage sections, I guess it acts like an op-amp or similar comparator type circuit with a reference to send a current sense signal back into the 'brains' of the unit.
@@LearnElectronicsRepair A current sense transformer like that designed to operated at AC mains frequency will very likely have a single turn primary and a secondary of perhaps a thousand turns.With all CTs you try to run the secondary so that its load is close to a short circuit. That way the current in the secondary is determined by the current in the primary divided by the turns ratio. The resistor used as the secondary load of course converts that to a useful voltage. On that circuit board I would guess it is being used to monitor current in the compressor.
Hmm, that many air conditioning systems must be a huge load on the power grid. Once I were in Greece and the power transformer near our hotel blew up in smoke. The local fire department unit tried to cool it down pouring water on it. Not sure how safe it was because nobody really disconnected anything, the sparks started flying.
Crude capacitive dropper running those poor SSR's. Cut the trace going down to SSR's and current limit your bench supply to under 25ma and move it up slowly to find out if the Zener diode still exhibit's the typical "knee" current behavior. Your FNIRSI DSO-TC3 tester could be handy.
Im guessing this is a class 1 board, as I see many class 3 MEC violations in the soldering... That aside... Why are you noy concerned about the discoloration on the high power 6 pin device??
hi,wanted to give you a hint on the invalid traffic issue,make a video requesting all your subscribers to disable AD blocker,if they dont see ADs it's actually affecting you the content creator,so please let them know
Power up the board and see if the power supply starts. If not then why? Imo, that switching supply needs to be on all the time for the rest of the logic to work
Pre-Covid I had a fascination with Fault Finding . I've lost interest now, mainly cos it's no fun tackling things alone. Better to bounce ideas ,off a friend & learn faster.
There's a very straightforward way to measure the voltage of a zener diode - not sure if you're aware of it? Make sure the zener hasn't failed open circuit firstly, to protect the circuit (if testing in-circuit, of course) then as long as the zener is ok you can find its operating voltage with a (backlight) LED tester. Easy and takes no time...
Hi Will. Yeah I've done that sometimes on video. In this case I never got so far as that because Detlef called in while i was working on it and after some googling he found some hi res pics of this board where we could read the value
Oh it's a cheap little USB chargeable LED flashlight from AliExpress. I'll show it on the next video and see if i can find the link. It's bright as f#ck!
I am a regular viewer and subscriber Richard but my concentration has been ruined here by the amount of adverts. Instead of following the topic I now spend my time anticipating when the next will come. Regretfully I am likely to de-subscribe and avoid in future.
I don't choose how many ads RUclips place in my videos. Some viewers also see more ads than others while watching the same video, possibly due to their location, and two viewers in the same location will often see different ads. I'm sorry to hear you are getting so many it has become a distraction. Really there is no simple answer to this. RUclips have to cover the costs of providing the streaming service, Creators have to earn a living doing what is for a lot of them a full time job making this content, and viewers need to have an acceptable viewing experience. I don't think myself that there are anywhere near as many ads on RUclips as there are for example on UK TV channels like Sky News or ITV which seem to carry about 15-20min advertising per hour of viewing. I believe US TV has even more advertising per hour. Where do you think the best compromise is regards ads vs viewing time? Another option is YT Premium, the viewer gets an ad free experience and the content creator gets paid for their work. It would be great to think of another business model that works for RUclips, creator, and viewer alike but unfortunately I can't imagine what that would be. Maybe it is unfair but I do feel that their are 'some' viewers who want to watch for free without being annoyed by ads and they think RUclips should provide a free storage and streaming service, using unpaid employees to run their business operation, so they can watch the content they like, made by creators who are getting no payment for their work. I honestly don't believe you personally are one of those people, though I believe that there are many who do fit that description, so maybe you could come up with some idea that would work better than the current situation.
This is supposed to be a story about fixing a circuit board without a diagram, instead we get all this crap about the weather!! Are you so desperate for RUclips time that you waffle about trying to stretch the video to falsly get money from RUclips. I hope others read this and realise they are being conned. RUNAWAY!!!!!
These are among my very favorite videos, where true skill and troubleshooting skills are put to the test. Random electronic, PCB failures. I love it. Well done!
Just to mention guys, I didn't have any high wattage resistors of the right value, so I used a couple of 51K and a 68K resistor in parallel (all 2W resistors) and this gave 17.5K which was close enough. The owner called me back the next day to say the aircon system was working perfectly. I think this is a large one which has four separate outlets (head units, whatever is the correct term) in different rooms
You remember the 4 circuits that you didn't understand the function of? They are communication modules, they communicate with the evaporator units. This board has 4 of them, but some boards have only 2, so the board supports only 2 units.
My calculation came to 18.5 K ohms, but still close enough.
*** - I'm not understanding how 51k and 68k = 17.5k ?? Wouldn't that be 119k ??
How did you come up with that total number? Or to know the value of that open circuit resistor?
@@romancharak3675 How? look at my comment below this...
How do you get this answer? I calculated 29.1 K ohms.
1/ 29.1 = 1/51 + 1/68
Some people just want to know the fix so they can get on with it and that's fine if you already have a lot of experience and understanding, personally I think it is great to see different peoples fault-finding methods as this is a skill in itself. Thanks for another great video.
Thank you Mr,There are few people who give their experience for free, and this is priceless
I have thoroughly enjoyed this video. I'm revising and prepping for 2nd interview and needed a PCB refresher. Really good mate. Millions of thanks.
You're welcome. Good luck with the interview 🙂
I am impressed with your knowledge and use of logic and common sense. Your dad seams very knowledgable too! Your video’s have helped me a lot. Much appreciated.
Yes, I was glued to the end. Your videos are the best. I'm a novice and I very much appreciate your very good efforts.
Fantastic. I appreciate you. I’m pro hvac, setting up electronics workbench to repair these, heat pump defrost control boards, gas furnace control boards and 3 ph dc and ac motor control modules….as they are very expensive ($300-1600USD) to replace. The only videos I can find require me to know Hindi although I’m trying to understand by watching their methods. Very similar to yours! If you get a chance to do more hvac stuff, jump on it. Take care.
You could also have used a small file or Dremel type tool to file one side of the resistor down.. you should be able to see where the resistor coil is broken/burnt and measure each side and deduce the value.
Oh that's an interesting idea 🙂
Yeah, same idea. Aren't those green ones wirewound resistors? Would make it easier.
I was going to suggest the very same thing but you beat me to it. I have done it many times on resistors that have blackened beyond recognition. It works well.
yes, This is something I practice myself too, I usually make a score in the middle and try to get a value from either leg to that and then double the reading you get.
@@Pulverrostmannen I like that!
I figured it out before you :), based on electrolytic rating, the zinner should be around 50 V. Zener current should be around 10mA. now 230-50/10exp-3= 18kOhms!
HIC = hybrid integrated circuit. Love the channel!
Keep in mind that environmental factors also come to play.
I once had an MOV that was mounted close to an 800 degree heat source and that temperature melts solder connections.
In this case, most of the solder dropped out of the 120VAC power connection and left the connection intermittent.
I wouldn't expect this board to be mounted that close to a high temperature source, but that resistor could have created it's own source.
One thing that you didn’t mention that I couldn’t help noticing was all of those beautiful test points marked with voltages. So as soon as I could get this thing reasonably powered up, I would go to those test points to try and help narrow down any other faulty railson the board. It’s rare to have that kind of documentation on boards that I tend to get.
@kennymanchester I agree that is a good technique. If you watched the video all the way through, I did mention some of the ways I would have moved forward, including powering up the PCB. Purely by chance I had already found the fault before I got to that stage.
Excellent video sharing your thinking as you go ... you might treat yourself to one of those grinding pens to help get past the board coating which is indeed a real pain. 😀👍
Just an observation in the first 10 minutes; how nice is this cct board laid out? All of the components in straight lines, test point voltages marked and there is almost a schematic on the back.
Looks unusually well designed and service friendly with all the silkscreen markings.
Nice to hear some questions answered that I had without having to ask. Great video.
*** - Please show more IN-CIRCUIT testing... to help us diagnose without removing.. (if possible).. Also, VERY Good video.. Thank You...
This is god tier stuff. If only my school teachers made it this interesting 😂 probably wouldn't have skipped class nearly as much or got in half the trouble lol
Problem teachers do only their jobs,,,
Glad you have the wonderful weather. We had a tornado at 2:15 am (Central Florida), just north of my location. Not good weather but rather exciting, I guess (Sever Storm Spotter/Chaser). Thank you for your videos and taking the time to make the fantastic content! Take care!
just found this vid Richard, so using your expertise to try & fix my external General Air Con Unit problem of not communicating with the internal ones, wish me luck:-)
Wish you was my teacher in the 80s I was told my maths was bad but I learn from watching not reading so ended up doing DTP and data input because of my electronic teacher
Heya, always difficult to annalys a pcb if you don't know much about it, yeah oke you can do some basic measurements like you showed us. hopefully someone in the community knows this pcb that eould be nice. love to see these industrial repair video's it's quit differant
Good call breaking the unit down into 'modules'. The fact this particular resistor had its markings gone was also another clue ( usually a sign of heavy duty ) and then all the other stuff about how much it was likely dropping. I am curious tho, if it was an intermittent or continuous load that done for it. As you've hinted it is possibly down to a design/ specification issue, but it could also be something at the load end that is out of spec.
I've had some success figuring out damaged resistors like this by scraping off the coating and measuring as much of the carbon/metal film or whatever as possible. If you can measure from 1 leg to say half way and you get 10k , then you have an idea that it's probably in the 18-22K range. The resistance will be linear across the length of the resistor so it will scale linearly.
Work is getting in the way of watching these wonderful videos!
Love these type of videos and the comments.
as it's the first component out of the live it sounds like a fuse resistor ... and it should be a hi wattage low resistance value ... about1 or 2 ohms and at lease about 2 watts ... so it acts like a fuse ... there are lots of these fuse resistors in circuits ... and also there's way that you can measure a blown resistor is that you can cut it in half and measure them ... one should definitely give a vale .. and that value is just about the half of the whole resistor ... this is a common way to measure blown resistors in repair .. you can even measure both half resistors and add up ... try it on a healthy resistor and se that it works ... these resistors have a simple structure and you can measure them cut in half... if length one half is double the length of the other half the resistance should be about twice the other half also. just try to make a clean cut. first try on another resistor and find the best way to cut clean.
I just went through a summer of highs in the 47C range here in AZ USA. If you can imagine we are a skinny state. I traveled to one of our eastern northern states recently and everyone was the size of a grizzly bear. Heat is good.
First of all, thank you for taking us along with your analysis of what the modular buildup of this board. Hmm, the DC part of the Bridge Rectifier looks a bit rusty, but it may also be the lighting playing tricks on me. Also the blue boxes at 5:49 look like capacitors to me, not relays, since they are marked C10 and C9 respectively(edit...Yes, you confirmed that later in the video), but your camera view might be out of whack with what you are describing here. What I would really like to know: *Why* the fusable 18K resistor failed; i.e. what the underlying issue or event is that caused it to fail.
Apparently this is a common fault on these PCBs as some others who are more familiar with them have mentioned. Thinking about it, one end of that resistor is connected directly to 220V AC, and the other end connects via a rectifier diode to a DC rail somewhere in the region of 'less than 100V'. So there is quite a high voltage across it and it clearly passes some current. I expect it was underrated by the circuit designer.
@@LearnElectronicsRepairIn that case it makes perfect sense to choose a 5 Watt resistor instead of the original one rated at approx. 3 Watt. Still, if it's intended as fusable, you might not want to pick a too high value here lest you overload more precious components further on in the circuit in the case of a failure.
@@LarixusSnydes Yeah I agree, it is a 18K resistor and a common failure on these boards, though I did not know that at the time. I actually ended up use three 2W resistors in parallel, two 51K and one 68K basically because that is what I had. That gave a total of 17.5K, 6 Watts. Though one could reasonably argue that the 68K resistor is passing less current than the 2x 51K so the actual max wattage will be a bit less than that.
Here in Texas, until just recently, most days have been over 37!!
I pointed on the screen to that resistor right in the beginning since I saw a slight color change on the board :D Nice
Yeah it was a little bit darkened. Personally I thought it was not unusually so for a board that has power resistors so didn't initially go to it. Well done 🙂
@@LearnElectronicsRepair Still very informative to see how to find it. Especially how to test relays in circuit, it's usually a pain to desolder.
Loving this videos, I'm learning lot of new things.
Gentle use of a hot air gun is best for tricky boards with lots of copper etc., take it slow and heat it up gradually so everything heats up evenly and you don't burn stuff.
14:23 "what's this thing here" and "this big thing" -> reminds me of the movie "My Cousin Vinny" where Vinny cross examines the eye witness and asks "what are these big things, asking about bushes or trees.
Also, so do you live in Maspalomas? Where are you originally from? What's it like to live in Maspalomas? Apparently it is often hot there, which makes sense, eh?
You might have to do a video on fixing a board with schematics, as I've never done that before, lol.
Thanks!
Very nice teaching video, thank you
53:33 can you link the video you’re mentioning here? Thanks ❤
Can you expand the in picture of the multi meter so we can see what settings you keep moving it to, thanks
Well I considered part of faultfinding is seeing if anybody else has a fault with the item I'm working with. Hate looking up a video may or may not help me send you on a wild goose chase for it may actually be the problem you're helping. She usually never the problem I'm having which is why I need to start making more videos.
I know the unit looks new but I would also check the electrolytic caps with an ESR meter just to make sure they are within specs.
We can measure where AC and DC voltage from the 220 input to the end of the circuit with a multimeter, how can we find the fault by measuring the voltage from the electrical input to the end of the circuit. What are the parts used for?❤
Which camera are you using to inspect the board and record please Richard?
I use a Sony HD camera mounted over the bench, similar to this one (I would have to check at the office to see the actual model) This is the one I am using to inspect the board
www.ebay.es/itm/145331094527
I use a cheap 2K webcam mounted on one of the monitors for the 'face' insert - this one
www.aliexpress.com/item/1005005305292588.html?af=ler2022
Another cheap 1080p webcam taped on to a flexible tripod originally meant for mobile phones for 'multimeter' insert - this one
es.aliexpress.com/item/1005004711460364.html?af=ler2022
And a 1080P C Mount ELP camera with 5mm-50mm zoom lens on a desk tripod for side views
www.aliexpress.com/item/1005004229884372.html?af=ler2022
I also use this THERMAL CAMERA (with the optional macro lens)
Infiray P2 Pro
s.click.aliexpress.com/e/_Dmuj4a7
amzn.to/457PgEb
www.banggood.com/custlink/DDGPI7hRvU
And I have a HDMI camera on my optical microscope, the Andonstar AD407 and a second PC to view webpages etc, plus another capture card for output from GPU or motherboards under repair. I record everything 'live' with picture-in-picture using OBS Studio (free) and I edit my videos with Davinci Resolve (free)
Will there be a video on all you need to know about relays? btw it seems that ads are back on sorin's channel i got 1 or 2 ads playing before the video starts but i don't see any on your videos it's quite strange
Please can you lecture more on this power supply because I want to know how fix electronics
Just been surfing the web and to replace that board costs 685 euro. wow 😁
That does not surprise me at all!
Curious why manufacturers which use PCBs, do not provide board/wiring diagrams, component I.D., and obvious test points so board evaluation can be done quickly?
It would also seem that PCBs can be designed with "self check" circuitry which would indicate board function at a glance.
Thanks for helpful video
Hi, Any chance of fixing the circuit boards on a Miller Dynasty 200 DX, there is a forum on the web out of NZ called element14 from NZ, And from reading their forums a number of people, say that it is impossible to reverse engineer the Miller Dynasty 200 DX circuit boards. But when I saw your video, I thought you know your stuff and I reckon if anybody could do it, It would be you !
Any chance of laying their frustrations to rest and taking on a challenge no one has conquered ! A series with many parts and stages, explaining how to trouble shoot etc ... would be Awesome ! Please would you think about it !
Richard first very descriptive video.Have you made a decision on your teaching videos? Maybe if you can a good class i feel is one just explaining circuit board layout. Some of the symbology and how to know the difference between the higher voltage area and the lower voltage. I haven’t see videos explaining circuit board layout. Stay well. Artie. 👍
Yes, I'm going to make teaching videos starting next week and see how it goes.
A great video! However you drive me crazy bending those components back-and-forth. A small angled dental mirror will get you the information you need behind these parts without risk of snapping off a pin and inducing another problem.
You had over 30c/26c at night in October? Wow, that´s awful. I too live in a house with bad(none) insulation and such temps as You have to bare would make my place a foundry, too.
How fitting to repair an aircon, eh?
I like to watch Your stuff, I have an old Radford TT100 I cannot figure out. Would You dare to take on a TT100? Kind Regards
Look at the Voltage rating of the zener diode. (Vz) Look at the wattage of the zener diode (Pz). Calculate the maximum current in the zener diode (wattage/voltage) Iz = Pz/Vz. This current (Iz) is the RMS current. The current in the zener might flow in pulses exceeding the RMS current (Iz). The same RMS current (Iz) flows through the resistor(Ir=Iz) (if you ignore the load parellel on the zener). The supply (240V) is a half sine. It's RMS voltage is 120V (240V/2). Substract the RMS voltage of 120V and the zener voltage(Vz). The result of this substraction is the RMS voltage over the resistor Vr. Now divide Vr by Ir (R=Vr/Ir). This is the resistor value you need. Take R 30% higher for safety. I assume the load parallel to the zener is around 1/10th of the load of the actual zener itself (which is typical).
For instance : Pz=0.5W Vz=50V -> Iz = 10 mA -> Ir=10 mA Now Vr = 120V -Vz = 70V -> R = 70/0.01 = 7 KOhm Take + 30% -> At least 10KOhm.
Thanks Kris. It turned out to be an 18K resistor, either 3W or 4W though no one seems certain of the wattage. Your formula is good as you got somewhere in the ballpark with a lot of assumed values. 🙂
Yep, calculating something like this should be only a last resort, as the designer knows all the parameters.@@LearnElectronicsRepair
Zeners aren't resistors (well, duh!) They are rated for *average* power, from which you can calculate the average current rating. They aren't rated for RMS power because it makes no sense. The power in the resistor is indeed a function of the RMS current, however the resistor current and the zener current are not equal. The instantaneous resistor current is equal to the sum of the the instantaneous load current and the instantaneous zener current. If the load is resistive and that resistance is known, then its current will be equal to the zener voltage divided by that resistance. You simply can't ignore the load current in design of a zener regulator circuit. Matters are further complicated when capacitive filtering is used. If the capacitor is directly across the zener it will do nothing of value unless you allow the voltage to drop below the point where the zener is conducting. That means that when the instantaneous input voltage rises above the capacitor voltage the current through the resistor will have to charge the capacitor. That cam make the overall RMS resistor current higher than predicted by "rule of thumb" esitmates.
The RMS value of a half-wave rectified sinusoid is not half the RMS value of the full sinewave, it half of the _peak_ value of the sinewave, taken over the full cycle period.
First of all, yes, I should have talked about average zener current. In typical zener design the load current is about 10 times smaller than the zener current. I am aware of that error. We're trying to get an idea of the range of the resistor. The capacitor just acts as an energy reservoir. It does not consume any active power. That is the reason why I only use RMS values. During normal operation the voltage over the cap is the zener voltage.
The amplitude of a 240V AC signal is 240*sqrt(2) volt. To get the RMS of the half sine wave you've to divide this amplitude by (2*sqrt(2)) which gives you 120. The voltage over the resistor is actually not a half sine wave, it's more like a half sine wave cut off from below. And you would need to calculate some integrals to get he RMS voltage. I know I make an error here too. I know I cut many corners.
If you want to have an more accurate estimate you can run a simulation in SPICE, using a load current of 10% of the zener current.
@@d614gakadoug9
Great Video...
About the unknown resistor: could You take away the outer coat with a Dremel (I assume that´s a wire wound) and measure from the fault to the ends to add up the results? Could it be that rather simple?
Well, this isn´t my idea, I stumbled upon it in here somewhere in time. I´d try- the part is already broken.
Expecting current limit sufficient to protect "sensitive" circuits by setting the current limit on a bench supply is folly! You will get current limiting ... eventually - after the output capacitors in the supply have sufficiently discharged. In the mean time you could get a current transient that could be tens of amperes even with a fairly small supply.
If you must use this method, the leads from the supply should be kept short circuited until it is time to apply current to the thing being tested.
Fair comment, probably better to add an LM317 to the output of the bench PSU to set a current limit using that. Generally speaking though this method is fairly safe when testing relays in circuit as the applied voltage is only the same as the switching device would apply to the relay coil anyway. I don't recall anything ever being damaged when I've used this method in the past but of course there will always be exceptions.
@@LearnElectronicsRepair
For lots of things there is no issue, but you can turn semiconductors into light emitters, even if they aren't intended to be, and LEDs into DEDs.
If that engineer gives up a spare board then I’ll eat my hat 😂
I'm late to this but your comment catches my eyes.
What? Do you mean the engineer won't gave a spare board because he may be scare for the life of the board?😆
If you use the continuity tester, it would not be advisable to connect the - pole to ground, because the multimeter injects up to 5 volts and this can destroy components. Plaese measure the volts at the test terminals of your multimeter!
Tip: Only use multimeters that inject 1 volt!
I have an Asus M2N32 sli motherboard that stopped posting. I tested all the voltages at the psu and all are good. When I plug in the 24 pin connector with the ATX 4 pin, nothing runs, but the standby led lights (on motherboard). If I unplug the 4 pin connector, everything runs but no post. All 4 pins on the connector socket show continuity to ground. Any ideas how to diagnose the component(s) causing this short to ground?
Maybe it's too basic for this video, but what I'm missing is what particular test u perform with the multimeter (the settings).
Thanks great vid you are good at reverse engineering.
Why didn't the aircon tech just replace that resistor, they know what the common faults are but just want the margin they make by being a board swapper and not a technician. Most of them are clueless fraudsters.
I'd wish some aircon techs were board swappers. Nowadays quite a few aircon techs simply see the entire outdoor unit or indoor unit as the only parts in the system to be changed - the idea of a tech opening up either unit to do anything fault finding is simply not worth the time when a new replacement unit might only cost 400 euro.
resistor less than a dollar, they are just fraudsters that cause waste@@daviddeakin2172
Field techs dont fix board issues. For an AC unit the should be HVAC certified, at least thats how it is here in the US. So they would recharge or replace compressors, condensers, motors, the control board, and anything that can be repaired gets sent back to a manufacturing facility for rework and what cant get they probably have a contract with some company that handles E waste and then that company probably sells what can most likely has some value to salvage off it to grey markets in places like Mexico, or somewhere like Viet Nam for component stripping and salvage.
There is a slight burn mark around that resistor area, i would like to watch the next part where you figure out how to get that resistor value
If you watched the video through - Detlef called in and after about 20 mins on google, he found the value which is 18K 3W or 4W.
@@LearnElectronicsRepair Yeah i did watch the full video and knew about the resistor value but i wonder if there's a formula to use to get the value of an unknown resistor in a circuit especially the smd resistors are hard to know if they're burnt
When you use a multimeter in diode mode to see if there's a shorts on the capacitor rail, what reading should the multimeter give to indicate it's a short circuit?
next time scroll down the comment section to see if this guy responds ... HE DOES NOT
Generally a short will read zero ohms or very close to that. However, once you find a 'short' in diode mode, make sure that you double check in resistance mode. Some voltage rails my have very low resistances when the circuit is operating normally and also if there are a large capacitors on a voltage rail it may look like you have a short for a couple of seconds while the capacitors start to charge, then the resistance reading will start to increase.
@@ACommenterOnRUclips First let me apologise for taking 8 hours to respond to you. Now we have gotten over that, what was the question?
@@LearnElectronicsRepair LOL ... Once again they ONLY reply when you call them out ... LOL ...
@gonzagaribotti9852 YOUR WELCOME
@@ACommenterOnRUclipsI disagree. "He" responds more often than any other electronics youtuber I've seen.
The black transformer at the end of the board is a current sense transformer with a full-wave bridge rectifier on the output. After the bridge will be a low-value loading resistor - likely in the range of a few ohms to 100 ohms or so.
The switcher control IC is intended for use in a quasi-resonant circuit where a snubber is not required, hence none is shown on the typical ap circuit on the datasheet. Note the cap from the FET drain to ground. There is no evidence of such a cap on the PCB (typically would be a moderately large type with polypropylene or "better" dielectric. It looks to like the circuit on the PCB is a conventional flyback.
Thanks for confirming my suspicion that this is a current sense transformer. It looks like it connects (after the four diodes/bridge) to the black module on the right of the PCB below it. This has high and low voltage sections, I guess it acts like an op-amp or similar comparator type circuit with a reference to send a current sense signal back into the 'brains' of the unit.
@@LearnElectronicsRepair
A current sense transformer like that designed to operated at AC mains frequency will very likely have a single turn primary and a secondary of perhaps a thousand turns.With all CTs you try to run the secondary so that its load is close to a short circuit. That way the current in the secondary is determined by the current in the primary divided by the turns ratio. The resistor used as the secondary load of course converts that to a useful voltage.
On that circuit board I would guess it is being used to monitor current in the compressor.
Hmm, that many air conditioning systems must be a huge load on the power grid. Once I were in Greece and the power transformer near our hotel blew up in smoke. The local fire department unit tried to cool it down pouring water on it. Not sure how safe it was because nobody really disconnected anything, the sparks started flying.
Check that zener under that brroken resistor
While looking at the board, I saw a resister that has overheated and a solder connection that could be intermittent.
hi, It's an 18 K resistor , from a Daikin AC unit :) 3 to 5 Watts likely
How would you diagnose that, if you only have the PCB, a multimeter, and have never seen one of these before? 🙂
@@LearnElectronicsRepair Easy ... I came to the same conclusion after watching the vid to the end.
@@I_Don_t_want_a_handle Hehehe well done
Crude capacitive dropper running those poor SSR's. Cut the trace going down to SSR's and current limit your bench supply to under 25ma and move it up slowly to find out if the Zener diode still exhibit's the typical "knee" current behavior. Your FNIRSI DSO-TC3 tester could be handy.
Indonesia hadir menyimak
Im guessing this is a class 1 board, as I see many class 3 MEC violations in the soldering...
That aside... Why are you noy concerned about the discoloration on the high power 6 pin device??
hi,wanted to give you a hint on the invalid traffic issue,make a video requesting all your subscribers to disable AD blocker,if they dont see ADs it's actually affecting you the content creator,so please let them know
Power up the board and see if the power supply starts. If not then why? Imo, that switching supply needs to be on all the time for the rest of the logic to work
Is it a good business to start, repairing circuit boards?
Who install to about a specific board? Wanting to learn how to repair furnace boards
i got a fridge board here that i cant read any components because of the coating they put all over it on both sides.
Pre-Covid I had a fascination with Fault Finding . I've lost interest now, mainly cos it's no fun tackling things alone.
Better to bounce ideas ,off a friend
& learn faster.
There's a very straightforward way to measure the voltage of a zener diode - not sure if you're aware of it? Make sure the zener hasn't failed open circuit firstly, to protect the circuit (if testing in-circuit, of course) then as long as the zener is ok you can find its operating voltage with a (backlight) LED tester. Easy and takes no time...
Hi Will. Yeah I've done that sometimes on video. In this case I never got so far as that because Detlef called in while i was working on it and after some googling he found some hi res pics of this board where we could read the value
i use this to fix my tv
Please, can someone tell me what the author used to x-ray the printed circuit board 15:20
A flashlight….? No x-rays involved, just visible light 😜
@@toolsarecool thats right) Im not native english speaker and I use translator for some words. But Im still waiting for help)
@@toolsarecool It doesn't look like a very ordinary flashlight
Oh it's a cheap little USB chargeable LED flashlight from AliExpress. I'll show it on the next video and see if i can find the link. It's bright as f#ck!
@@Максим-х7и1пneither am I. No ill will intended. Just looked like a bright light, maybe USB powered
(Edit: oops, just saw Richard’s response)
Hi. Do you have an email I could send a video of my faulty lcd speedometer. Hopefully you can point me in the right direction.
I see lots of ads now, as before. I think your invalid traffic problem might be over.
Looks like DAIKIN Outdoor unit PCB........
That same thing as my cheap portable AC, ie, a wire-wound resistor or inductor - it looked like a white coloured resistor - blew open like a fuse
The failed resistor is apparently a common fault of these Daikin AC units ruclips.net/video/SZz16VphtKE/видео.html
This series from Haseeb helps a lot understanding these AC boards...
ruclips.net/video/X0JX99QwyTs/видео.html
Yeah Haseeb makes some good videos, I'm a subscriber. It's interesting how similar our techniques are when faced with the same sort of repair work.
Friggin mitsubishi.
Why don't you just use a Hakko desoldering gun, would make your life so much easier?
Awesome stuff
But your voice makes me sleepy
😂😂😂 33 dwgrees is extreme hot??😂😂😂
At your age, are you sure that is sweat at night and not an accident? 😄
PMSL. But no it's not PMS at night LOL 🤣 it's at the wrong end of the bed to start with
I am a regular viewer and subscriber Richard but my concentration has been ruined here by the amount of adverts. Instead of following the topic I now spend my time anticipating when the next will come. Regretfully I am likely to de-subscribe and avoid in future.
he does not care ....
I don't choose how many ads RUclips place in my videos. Some viewers also see more ads than others while watching the same video, possibly due to their location, and two viewers in the same location will often see different ads. I'm sorry to hear you are getting so many it has become a distraction. Really there is no simple answer to this. RUclips have to cover the costs of providing the streaming service, Creators have to earn a living doing what is for a lot of them a full time job making this content, and viewers need to have an acceptable viewing experience.
I don't think myself that there are anywhere near as many ads on RUclips as there are for example on UK TV channels like Sky News or ITV which seem to carry about 15-20min advertising per hour of viewing. I believe US TV has even more advertising per hour. Where do you think the best compromise is regards ads vs viewing time? Another option is YT Premium, the viewer gets an ad free experience and the content creator gets paid for their work.
It would be great to think of another business model that works for RUclips, creator, and viewer alike but unfortunately I can't imagine what that would be. Maybe it is unfair but I do feel that their are 'some' viewers who want to watch for free without being annoyed by ads and they think RUclips should provide a free storage and streaming service, using unpaid employees to run their business operation, so they can watch the content they like, made by creators who are getting no payment for their work.
I honestly don't believe you personally are one of those people, though I believe that there are many who do fit that description, so maybe you could come up with some idea that would work better than the current situation.
@@LearnElectronicsRepairWOW thats usually how you guys answer, you get called out LOL ...
what about responding to the other comments ??
YOU, @kvppvk could SKIP the adds but then @LearnElectronicsRepair wont get $ paid $
This is supposed to be a story about fixing a circuit board without a diagram, instead we get all this crap about the weather!! Are you so desperate for RUclips time that you waffle about trying to stretch the video to falsly get money from RUclips. I hope others read this and realise they are being conned. RUNAWAY!!!!!
You have moustaches on each of your fingers.
Cheeky. FYI I'm smuggling caterpillars 😆