Itek Atx 500W does not turn on

[falcontech]

Hello everyone
I'm back with another ATX that doesn't want to leave, with the experience of technoware I did the same tests you recommended me, the structure is very similar, on the primary the voltage on the large capacitors is good, I tried the voltage on the transformer small and I have 5,7 volts, I have 5v standby, I have 8,5 volts on pin 12 of the integrated circuit, the mosfets on the primary and the shottky diodes on the secondary are fine, when I turn on the power supply I have about 6 volts for a few seconds on the line of 12 volts which then vanishes on 5 volts nothing and not even on 3,3

[CapLeaker]

Re: Itek Atx 500W does not turn on

First thing we need is always pictures! Power supplies aren’t always built the same. Some have PFC others don’t. The valuable info just gave is, the PSU actually tries to start, but gets shut down, because something doesn’t add up and the protection circuit clicks in.
Again, test each individual voltage rail on the secondary output and turn the PSU on. Write down what you measured on each rail. Don’t forget the -12V!

[falcontech]

Re: Itek Atx 500W does not turn on

Ok

[falcontech]

Re: Itek Atx 500W does not turn on

here are the photos, I tried the rails, on the -12 volts I have a departure of about 14 volts which then vanishes, on the 3.3 I have 0.3 which then goes away, on the 5v I have nothing

[falcontech]

Re: Itek Atx 500W does not turn on

I forgot I tested the two c945 transistors between the primary and the secondary and they are good

[CapLeaker]

Re: Itek Atx 500W does not turn on

I see bad solder joints all over the place. Fix those first. I guess the power supply is shutting down because of not having any 5V. Check the diodes for the 5V and 3.3V rail.

[CapLeaker]

Re: Itek Atx 500W does not turn on

I forgot I tested the two c945 transistors between the primary and the secondary and they are good

Doesn't surprise me, because the PSU is turning on, then shutting down. So the primary side must be working.

[falcontech]

Re: Itek Atx 500W does not turn on

ok, unfortunately there was something sticky about the welds that didn't allow me to make good welds, what are these diodes? you could indicate them on the photo thanks

[falcontech]

Re: Itek Atx 500W does not turn on

are you talking about the schottky diodes those in the heatsink?

[CapLeaker]

Re: Itek Atx 500W does not turn on

clean the bottom of that board first with IPA or Acetone and an (old) toothbrush. That crud has to come off. Then fix what you see is broken, as I see quite a few bad solder joints that are cracked, have rings, aren't soldered properly, one looks like its touching something else, etc.
After cleaning, fix all the bad joints and retake the photo.

First photo, second heat sink from the left. Check the components mounted on it.
The single blue wire is -12V, the orange wire is 3.3V, the red wire is 5V, etc. Trace it back and check it for a short to the black wires (GND). Either something is a dead short or an open.

IPA = rubbing alcohol

[CapLeaker]

Re: Itek Atx 500W does not turn on

are you talking about the schottky diodes those in the heatsink?

yes

[falcontech]

Re: Itek Atx 500W does not turn on

I had already checked the three schottky diodes and they were good, they did not give me any short, the capacitors I had replaced them all, they will make one that I will now do, the welds you see open are from the heat sink, I have not welded them in case I have to disconnect again the heatsink, now check the short on the blue, red and orange wires

[falcontech]

Re: Itek Atx 500W does not turn on

I used trichlorethylene to clean but the dirt doesn't come off

[CapLeaker]

Re: Itek Atx 500W does not turn on

Is there something open like an inductor, or transformer winding?

[falcontech]

Re: Itek Atx 500W does not turn on

I checked the tracks and it gives me the short on the 5v and on the 3.3 but I noticed that the short on the 3.3 also gives it with a working power supply, I replaced the large coil on the secondary, it was all burnt out, I took one from an old atx, the original one had 8 pins, the one I replaced has 10 and I left two unconnected could it be that?

[CapLeaker]

Re: Itek Atx 500W does not turn on

no short on the working PSU on the 5V rail?

[falcontech]

Re: Itek Atx 500W does not turn on

no

[CapLeaker]

Re: Itek Atx 500W does not turn on

investigate that. maybe a zener diode is shorted. Take the shottky diode off the heat sink and see if the short persists. If the short is still there, you have to check every part on the secondary that is on the 5V rail.

[falcontech]

Re: Itek Atx 500W does not turn on

ok, but what about the big reel? can that go, which i replaced?

[CapLeaker]

Re: Itek Atx 500W does not turn on

That is an inductor. It could go open. maybe put the old one back in place.