Restoring ATX supply for learning purpouses.

[Francesc V.]

Hi:

I am trying to repair an ATX power supply, where "everything" blow up.

- The Fuse
- The Diode bridge
- the 2 "mosfets"

I would like to ask you about the "mosfets" because when I look for the reference 13009 they seem that they are NPN transistors. (hopefully attachment is inserted).

2+1 questions I would like to raise.

- Does the brand that appears on the chip looks familiar? it's not ST, right?
- Are these NPN indeed?
- With all the listed casualties. From your experience......anything else to look at? PWM chip?? (schottky diode are ok).


Thanks in advance,
Francesc.

[Francesc V.]

Re: Restoring ATX supply for learning purpouses.

In the meantime, I've removed 2 burned resistors that connects the base and the emitter from the 2 transistors and I guessed a 470ohm value (altough burned, one was measuring this value and the other one was 680ohm).

Also, in case the PWM chip would need to be changed, I am not finding anywhere this chip (SHJ1512A).

[R_J]

Re: Restoring ATX supply for learning purpouses.

Use the second number on the ic, I believe its equivalent is a CG8010, check the pinout
Those 2 small electrolytic's (C7, C8) near the mosfets will be bad as well

This site might help https://danyk.cz/s_atx_en.html

[redwire]

Re: Restoring ATX supply for learning purpouses.

The black spot on the transformer, is that from an arc inside the windings or schrapnel from transistor popping?

This is cheapened, they have jumpered many parts out. No X cap or CM choke but... the NTC inrush thermistor TH1 is jumpered out and of course the bridge rectifier sees stress.
The transistors are MJE13009 (or ST13009, FJP13009), they are not mosfets.
I would also replace the small electrolytics C7, C8.

[R_J]

Re: Restoring ATX supply for learning purpouses.

Correction
Q01 & Q02 13009 are not mosfets, just transistors

[PeteS in CA]

Re: Restoring ATX supply for learning purpouses.

The MJE1300# are bipolar transistors, originally of the 1970s vintage Switchmode series from Motorola. The MJE1300# are in the TO-220 package (originally, at least); the 2N654# were of the Switchmode series, but in the TO-204 ("TO-3") package.

The MJE13007 and MJE13009 are examples of parts that work too well to kill off, though the trend toward higher efficiencies will accomplish that sooner or later.

[redwire]

Re: Restoring ATX supply for learning purpouses.

I think the transformer might be pooched?

[Francesc V.]

Re: Restoring ATX supply for learning purpouses.

The black spot on the transformer, is that from an arc inside the windings or schrapnel from transistor popping?

You scared me......I didn't see it before. It's a black spot but from silicone

Use the second number on the ic, I believe its equivalent is a CG8010, check the pinout
Those 2 small electrolytic's (C7, C8) near the mosfets will be bad as well

This site might help https://danyk.cz/s_atx_en.html

Thanks for the reference.......I will check the pinout.
I've removed the capacitors. They are both 10micro 50V.....but just rate 9. I've ordered a few. Is this value critical? If not, I could use 22micro 50V (from this I have a few).

Thank you ALL for your feedback. Yes!! a really cheap ATX PSU........today I've realised that you can get an ATX PSU from 15€ to 900€ (this one with GaN Mosfets!!). World is crazy.

Regards,
Francesc.

[Francesc V.]

Re: Restoring ATX supply for learning purpouses.

Pieces arrived (bridge, NPNs, Fuses).....

So I replaced all of them but.......current situation is that SMPS has 5V Standby only (and 5V in the green wire also).

When I switch on the SMPS by shorting the green wire to ground, there is not output (3.3V, 5V, and 12V).

However:
1. The SHJ1512A / CG8010 has Power in pin 13.
2. Pin 7 and 8 measure 37kHz......so it seems that is oscillating
3. These signals arrive to Q3 & Q4 Base transistors.

Could you please provide me some guidance about what I should measure next?

Thanks in advance.
Francesc.

[stj]

Re: Restoring ATX supply for learning purpouses.

look at the parts between the driver chip (pins 7/8?) and the transistor base pins
when they shorted they usually damage the drive circuit

[stj]

Re: Restoring ATX supply for learning purpouses.

looking at the pictures,
check the resistors
47ohm (yellow purple black black)
and the small ones - brown,black,gold < bet those are fucked!

[Francesc V.]

Re: Restoring ATX supply for learning purpouses.

Q3 (C945 NPN) was bad, so I've replaced it.
I've also checked optocoupler and it's ok. Between pin 1-2 I have 1.1V and in pin 3-4 0.7V

Could be XY6112 faulty?

- Between Pin 2-3 there are 5V
- In Pin 7-8 about 320V dc

Is there any procedure to test/validate this chip?

(I'm using an old photo where some components have already been changed and the Big power transistors soldered )

[stj]

Re: Restoring ATX supply for learning purpouses.

you have burned out resistors in your picture

[Francesc V.]

Re: Restoring ATX supply for learning purpouses.

I must admit that you were absolutely right @stj. Thanks for your perseverance pointing at the resistors several times in the post.

Two 1ohm resistor in previous picture were open. Now I am posting the final picture



So Now, it switches on and it has all voltages!!



However, I started testing it and requires some adjustments.

I connected the SMPS to a motherboard with embedded graphic card, and a SATA Hard Disk. I have started to install the operating system until the system shutdown about 20 minutes later.

Now the SMPS tries to swich on and then switch off and then again and again.........

Could it be the BIG capacitors?????? it has 2 in serial from 680microfarads and 200V. Although they have a low ESR, they only measure about 400. Or the problem is more likely on the filter capacitors on the low voltage side?? (all other capacitors on the hot side are already changed/measured).

Thanks in advance,
Francesc.

[Francesc V.]

Re: Restoring ATX supply for learning purpouses.

In the meantime I've removed all capacitors from the COLD part. All of them have LOW ESR and the right capacity.

[R_J]

Re: Restoring ATX supply for learning purpouses.

What voltage do you have on Q3 collector? if it was bad it may have damaged one of the resistors between the standby 13v and the Q3 collector.

[Francesc V.]

Re: Restoring ATX supply for learning purpouses.

Both Q3 and Q4 were replaced with new C945 transistors. Now when the SMPS is switched on without any load I have the following

- 2.21V coming from "CG8010" chip to the base of these transistors.
- 2.06V in the collector
- 1.54V in the Emitor.

Outputs without load:
5.05V
12.12V
3.44V

"useless info": The SMPS has two TL431. They have 2.5V in the reference pin and 3.92V and 2.75V in the catode outputs.

I have an osciloscope if you want that I measure anything in particular. Never used it, but I have it.

[R_J]

Re: Restoring ATX supply for learning purpouses.

The collector does seem low, The small drive transformer that is connected to the two drive transistor collectors is supplied by the standby transformer (the smaller diode off the standby transformer supplies 12v)
When there is no load and the circuit operates, the 12v to the drive transformer is supplied by the main secondary 12v through a blocking diode.
I would check that the resistors between the standby 12v and the drive transformer, If you have not replaced the small electrolytic on the standby 12v supply I would.
I will try and find a schematic that shows that circuit.

[Francesc V.]

Re: Restoring ATX supply for learning purpouses.

Thanks in advance.
So now the SMPS seems to work. At least right now and from the last 2 hours. I tested under load using light bulbs simulating load in the 3 rails (3.3, 5 & 12)..........and the PG signal was always ok.

Then I assembled in a PC (the one I am right now using for this post) and it's working fine..........not sure what to think. Maybe a wrong/bad connection...........or something that I de-soldered and soldered again.

It has been worth it a lot trying to repair it...........not for the materials and the hours invested. :-)

Regards,
Francesc.