Seasonic power supply repair. APFC fault

[@Zerous_12]

Where do you get the CM6500UNX? What is your store to get components?

[@electronicshaverightstolive]

I don't have a specific store for buying components. The whole Aliexpress is my store :). Sometimes they send faulty components, sometimes used ones which is ok for me. For those who have money check mouser or Digikey.

[@saarike]

Great!!! Thank you.

[@theivan5590]

The best for repair :)

[@electronicshaverightstolive]

Thank you! :)

[@coloradowilderness3139]

University should concentrate more on repairing level skill building for EEEs.

[@IgorPichugin]

What is the labeling of bipolar smd transistors?

[@mjan21]

Nice job. Do you know what caused the PFC to fail?

[@electronicshaverightstolive]

Thanks. I don't know for sure. I was expecting it to be a faulty bulk capacitor but it wasn't. May be it was due to overheating or overloading.

[@sanelleric6121]

Fuse didn't probably blow up due to NTC series inrush current limiting resistor on the capacitor bank.

[@electronicshaverightstolive]

Sometimes FETs fail in open circuit. That was the case here. Probably NTC helped to limit inrush current. But if FETs fail in short circuit NTC would heat up and fuse would blow anyway.

[@bzfarbodjz]

how do you found the vale of those smd resistors without schematics ? it's not written on

[@Shmbler]

That's obviously not his first Seasonic PFC stage since he already has the required parts at hand ;-) Resistors in series with MOSFET gates always have a pretty low resistance anyway.

[@tommybulyan]

Something i hate when i see high power transistor is blow up.. Mostly ic controller also blow up.. And difficult to find replacement

[@electronicshaverightstolive]

@@tommybulyan yes. That's true.

[@thangpham6942]

my sesonic 520W power supply has 5V stanby, power on has 5V red line, 12V yellow line but orange line has 1.5V please help me!

[@taskinyucekurt]

Good job. Fuse is good, strange ? let me tell you what i did and fuse was still ok. 600w power was collapsing at 300 350 load, took it out of the case and started to measure outputs which was also ok., then i turned it off but i forgot about hot ground left the cable attached to the wall jack. Grabbed a screw driver and stick it in to power supply thru fan to raise output voltage a bit cuz it is adjustable, then boom hot ground shorted to output schottky rectifier's cooler lol Guess what happend beside power in the house was gone, bridge rectifier, power transistor, a path which goes to base of that transistor also was gone, few resistors at the high side was gone, whole high side was short. But voila fuse was super ok yet lol even i connect it back to the cable and blow breakers again still fuse was ok. Changed power transistor and bridge rectifier then 5v stby came back. Then changed rest of the cooked components and repaired broken path then all voltages came back. And measured almost everything on the board and they all looks ok but all voltages drops down when i connect it to the motherboard and motherboard doesnt fully turn on when i attach a hard drive 12v drops to 9.5 v, when nothing is connected to the power supply everything is ok it is working fan is turning all voltages are exist. Seems like its a feedback issue but i couldnt solve the problem yet cuz board has 4 chips and another 2 under the high side and all seems ok too.I think i cooked main transformator but i'm not sure. Do you have any idea about this ? probably you are thinking that how that power supply still works lol and yes fuse is still ok.

[@electronicshaverightstolive]

Nice story you wrote. About your issue I'm not sure what is going on. It is strange that your PS works when voltage drops to 9 volts. All modern ATX SMPS have superviser IC which would shut down the main inverter if abnormal voltages are detected. So yeah there is probably a problem with feed back / supervisor IC.

[@taskinyucekurt]

@@electronicshaverightstolive Yes i've missed that you are right it should shutdown but keeps working. On that lil vertical board it does have 2 ics to monitor voltages and a line which drives 1st optocoupler( 2nd one is also ok but weird thing when its on it doesnt show short on buzzer mode at high voltage side, shows resistance. im not sure it is normal or not cuz 1st one shows short when power is on, basicly it should connect A to B right) . Another one on the low voltage side, pwm close to 5v transformator which is 7 pin one, single pin drain. I checked all those ics on diod mode also whole pins of vertical board. There is no short in anywhere except usual ones. I am so confused, hard to repair semi broken one lol. It runs like a champ if nothing is connected to it.