MYSTERY ATX PSU FAULT - SOLVED!!

[@jrmiller034]

That was a great repair. I am happy that you continued from the first video. I was afraid you wouldn't have. I have repaired many failed computer power supplies just because I can. I find it rewarding. Most have failing capacitors. I have newly subscribed to your site as of yesterday. Keep up the good work.

[@SeanChYT]

I had a similar PCB with very bad traces and pads. Bad quality one-sided PCB plus a lot of corrosion damage. (KEF subwoofer PSU) I decided to go the simple route and desoldered everything, scanned the PCB, recreated it from the scans, ordered new PCBs to be produced, reverse-engineered the entire circuit and found modern replacements of every part from Mouser, and then soldered everything together again.

[@Xorat]

Hey Richard, really glad i was right for the wrong reason haha. My sur name is german so it is basicly impossible to pronounce for non germans. A step up converter seems nice for that little thing. Maybe you could even do it battery powered or power it up with the bench power supply. But anyways, really happy that the mystery got solved and i was able to go on that Journey with you! best regards!

[@LearnElectronicsRepair]

And thanks to you too :D I am definitely going to try to modify that thing and make something that is actually useful out of it! Should make another good video too :D See you around my friend :-D

[@robinedminson6461]

I watched the first video last night and went to bed puzzling on your behalf. Woke up this morning and you only gone an fixed it. Well done. Great demo on perseverance in fault finding 🙂

[@LearnElectronicsRepair]

I wonder why some people don't like this video? I wish people who don't like videos would leave a comment explaining why otherwise how can I improve them?

[@hosseinebrahimi3451]

I watched both videos and enjoyed them. Since you've been curious about ways to improve your channel i might recommend you first work on audio. The most important thing in a KZbin content is audio. I feel awkward to brought this up but your voice when talking precieves tired and week and some people have sort of a sensitivity about this subconsciously. Thank you for your time and efforts.

[@LearnElectronicsRepair]

@@hosseinebrahimi3451 Hi - I asked so that is fair enough to comment. I've ordered a better microphone to help with the audio quality. I'll try to sound more dynamic - I think it depends on the day, what I am doing, and how well it is going. But I take on board what you say. Thank you.

[@hernancoronel]

To me both videos have been amazing and let me point out that being tired is being human. I didn’t perceive bad audio quality but I have to agree that great audio makes videos much much better, so thank you Richard for getting better audio equipment as I am sure we are already enjoying it as I am writing this one year after this video was posted. Keep up the great work!

[@gloubiboulgazeblob]

Maybe because those people are a bit too demanding on the quality of the video/sound : very often it's out of focus, or the subject is not in the center of the screen, etc...For the sound, well, it's ok for me... Anyway, my knwoledge in electronics is very basic, I try to repair my ATX SMPS and it's always interesting to follow your repairs, you take your time to analyse, desolder to test components, draw schematics, what tools you always use, etc...I still wonder how you manage to remove solder with your desoldering wire and flux, I tried, it never works for me (how hot is your iron in degree Centigrade, more than 400°C !?)

[@LearnElectronicsRepair]

@@gloubiboulgazeblob My soldering iron is set to 380C. I made a whole video explaining how to use solder braid, check it out. kzbin.info/www/bejne/pIO5fYirhLKKaKM Thanks for the suggestions, I have made several upgrades to the audio and video recording system since the video and I'm just about to upgrade again

[@cue108]

Just went through the full 2,5 hours of this PSU repair! Thanx for the journey and having a look over the shoulder of such repair job endeavors! -> Subscribed!

[@nigelfewster]

Just watched part 1 and had to find part 2 when you discovered your test equipment was not up to the job it made me laugh similar things have happened to me and I thought I was the only person this happens to. Love the vids and learning a lot.

[@sintifela]

Thank you very much for the video. I have a PSU with the same board which had almost the same symptoms. 5V standby was ok and there was no other voltages. It turned out to be that the solder junctions connecting the main switching transistors were broken. Resoldering them solved the problem.

[@stevieboi61]

i kno nothing bout electronic repair but feel like i wrkd hard watching you over a few videos. lol. ive learned a lot. thankyou.

[@ralphj4012]

I think the power supply monitor should be self-powered, so whatever is missing (12V, 5V standby etc) is obvious. Perhaps a separate 12V DC mains adaptor and a high side switch ‘OR’d with the 12V from the power supply or something.

[@wilsard]

take that tester apart and put a boost converter from the 5v standby to power it.

[@Dutch_off_grid_homesteading]

Heya love to see it's fixed

[@badboydas]

Loved the video, looking forward to the mod. As far as the dislikes, QUOTE John Lydgate“You can please some of the people all of the time, you can please all of the people some of the time, but you can’t please all of the people all of the time”. Personally I would not worry about it, I once didn't get a job because I don't always come across as enthusiastic, that was lucky.

[@LearnElectronicsRepair]

@Das bank I completed the Mod a while ago kzbin.info/www/bejne/r6iaZWqAYp55Z9U

[@oefzdegoeggl]

That was interesting. I'm currently trying to repair one (changed a MOSFET and a few capacitors) that has 3.3, 5 and 12 + standby all good, but it shuts down after a few seconds and then comes back another 10 seconds later, repeating. With and without load. The PWR_OK reads only 0.32V as well. I wonder what I should check next, the switching itself should work fine, otherwise I'd assume never to see good voltages at all.

[@estartermanual]

thanks for your contribution

[@chinnarao326]

Vaav Class Super Sir. -- ChinnaRao Paderu Andhrapradesh

[@ratbag359]

Very nice. fooled by the anilizer again. Ir really should power itself off the 5vsb.

[@LearnElectronicsRepair]

Yepp - and I won't get fooled again! I hope. I'm going to try to modify it as I mentioned. Really what is the point of an analyzer that is basically only useful for analyzing a PSU that is already working! I would have expected the designer to have thought of that already. DOH!!

[@Adrian_Finn]

@@LearnElectronicsRepair I have the same device! God I'm glad I watch these videos!! Surely there has to be a better device out there for this stuff.

[@LearnElectronicsRepair]

@@Adrian_Finn Or maybe I can try to make this thing actually useful!! Watch this space!

[@hernancoronel]

@@Adrian_Finn the modification is done here: kzbin.info/www/bejne/r6iaZWqAYp55Z9U. Hope this helps!

[@carterwheat7644]

Your power supply tester, you have to plug up both ends of the tester .

[@krakadoros8605]

Excellent repair. Can you please help me or give me an idea about what may be the reason of a strange behavior of my PC PSU ? It is a new one Corsair 650 Watt. I would not pay attention if it would not make a strange noise every 5-10 seconds. It is something like a cat's meeaou.... (i think the right word is" whine") I look close enough and see that its fan (inside the PSU) spins and stop in a loop of 5-10 seconds (but this is not every time happens. It happens very often, some time from the beginning of PC's booting). I give it to the store i bought and they told me that there is no such a problem. Probably they do not test it for a long time, so the problem did not come out. I do not know if this "on-off loop" of the fan, is normal. It is for sure that the noise accompany this loop, is very annoying and do not let me work with the PC. The PC works fine, even this loop is present. Something i must mention is that my motherboard is old, so the connection between the PSU and the motherboard comes with an adapter cable, but because i did not find the right cable i left 4 pins out. I mean that the PSU cable has 24 holes and the motherboard insert has 20 pins. So it needs a cable with 24 pins in one side and 20 holes in the other. Instead of this, i found a cable with 24 pins in one side and and 24 holes in the other, so i left out (not connected) the 4 holes in the side that connect with the motherboard. If this loop is normal, i must, anyway, stop the noise. I notice that the noise comes from the central part of the fan. I think that is the coils inside the fan, that vibrates. Any help will be welcome.

[@daz41262010]

awesome fault finding Richard :)

[@saarike]

Excellent repair! Thank you.

[@LearnElectronicsRepair]

Cheers! It was.... fun LOL

[@LearnElectronicsRepair]

Cheers!

[@fassesweden]

I have a PSU that have 5v stb dropping to zero within a few seconds . When turning it off on the switch it rises to stable 5V. Im guessing bad capacitor on 5v stb. Your thoughts?

[@latesttiktokvideos9388]

sir i have 500 watt psu with 12v coming on 5vsb and nothing on 12 5 n 3.3 v rails....can u help me fixing it...the ics are weltrend 7527 and tny 277

[@LearnElectronicsRepair]

Wow that's a lot of voltage on the 5VSB! Look at the TNY277, and also the feedback circuit through the opto-isolator. With the PSU turned off, connect a bench PSU to the 5VSB (purple wire) and put your multimeter in diode mode across the transistor in the opto-isolator. Look for a datasheet for the opto-isolator and connect your meter with the red lead to the collector and black lead to the emitter. Set your power supply to zero volts. The meter should read open circuit. Now increase the PSU voltage. When it reaches a bit over 5V (say 5.5V) the transistor in the opto-isolator should turn on and your meter reading should suddenly drop near to 0.00. if this does not happen then you have a fault in the feedback circuit. If you do have a feedback fault then to narrow it down a little further, put your meter in DC volts mode and connect it across the LED in the opto-isolator - red lead to Anode. Once again vary the bench PSU a bit above and below 5V. You should see the voltage across the LED suddenly jump up to around 1.3V when you go a bit above 5V. Now consider the possible problems: 1. The opto-isolator transistor does turn on when you have over 5V on purple wire. In this case you have a faulty TNY277 or some faulty resistor/capacitor near the TNY277 on the high voltage side. Reverse engineer (or find an example circuit for TNY277 in the datasheet) and you should be able to find the fault. 2. The opto isolator transistor does not turn on but you do get 1.3V or thereabouts on the opto-isolator LED with around 5.5V on the bench PSU. In this case you have a faulty opto isolator. 3. The opto isolator transistor does not turn on and you do not have 1.3V on the LED. In this case check the voltage reference (almost certainly TL431 or compatible). If that is OK look for faulty resistors, diodes, capacitors, bad soldered joints, broken PCB tracks in the 5VSB feedback circuit on the low voltage side. It would be best to reverse engineer the circuit between 5VSB, the TL431 and the opto-isolator LED and you should find the problem I hope that helps

[@andymouse]

Great video !...cheers.

[@anshifpa8011]

Amazing video I have a old psu (450w) and i was using it as a power supply but suddenly it stopped The IC is (SDC 2921) The standby 5V is good But iam only getting 3V as rem in the chip can this be the problem if it is can you tell how to repair it or bypass it ?

[@LearnElectronicsRepair]

Hi Anshif Check out this video, see if it helps you. kzbin.info/www/bejne/eZ3Ti5qBe9CNkKc

[@anshifpa8011]

@@LearnElectronicsRepair Thank you for the reply But I tried it I'm getting about 16V in there Other than that what could be the problem?

[@davidhollfelder9940]

Could I have fixed that? .. nope.

[@uksuperrascal]

HA HA you blame the PSU tester but the tester by not coming on showed no 12V. But Then you started at the middle of the circuit and missed the OP OC components - Been there done that too.HA HA - Work back from where there is no Volts to find Some Volts and there is your fault, As my old long passed teacher used to say.