Sorting out old PC power supplies?

[sam_sam_sam]

Re: Sorting out old PC power supplies?

Some more items that did not land into the landfill

Go repairs

[roadrash]

Re: Sorting out old PC power supplies?

Thanks RJ for that Schematic and thank you everyone for your help.
Thanks to you all I have finished repairing these PSU's and all the computers they go in are working again.
Thanks!

[R_J]

Re: Sorting out old PC power supplies?

Did you remove the main capacitors at any time?

If you are getting - voltage I think at least one of the caps are in backwards, see this picture from the internet.

This schematic should help with the standby circuit

[stj]

Re: Sorting out old PC power supplies?

high pitch sound usually means something is shorted.
check all ceramic capacitors

[roadrash]

Re: Sorting out old PC power supplies?

The small smd transistor drives a larger mosfet that has it's Drain pin connected to the small standby transformer, I made a Red square around the standby mosfet and a yellow one around the drive transistor.
On the small standby transformer, pin 1 should have 160vdc, and so should pin 3 which is connected to the mosfet drain., this is the primary. There is likely a low ohm resistor connected to THIS mosfet's source pin to hot ground.

That's a great help RJ. Ok I took a reading on all you said and I dont get a voltage on Pin 1 of the standby transformer (my meter just goes straight to zero whatever that means) although I do get -310vdc on pin 4 and -310vdc at all 3 pins of the smd transistor.
I am not sure if I am putting the negative meter probe at the correct place. I am taking the negative from the negative output of the Rectifier but all readings are -voltages which seams wrong. I always get confused where I should be taking the negative from especially on the AC side. I guess if I take it from negative output of Rectifier its got to be right (I hope). I also get a high pitched sound when turning the PSU on or off. Its what sounds like its in pain lol...

[R_J]

Re: Sorting out old PC power supplies?

160v??
where does that come from? he's got 340v dc after the rectifier.

It should have been 340vdc, I overlooked that he was in the U.K. next time I will just call it Main B+
EDIT

The small smd transistor drives a larger mosfet that has it's Drain pin connected to the small standby transformer, I made a Red square around the standby mosfet and a yellow one around the drive transistor.
On the small standby transformer, pin 1 should have 340vdc, and so should pin3 which is connected to the mosfet drain., this is the primary. There is likely a low ohm resistor connected to THIS mosfet's source pin to hot ground.

[stj]

Re: Sorting out old PC power supplies?

160v??
where does that come from? he's got 340v dc after the rectifier.

[R_J]

Re: Sorting out old PC power supplies?

The small smd transistor drives a larger mosfet that has it's Drain pin connected to the small standby transformer, I made a Red square around the standby mosfet and a yellow one around the drive transistor.
On the small standby transformer, pin 1 should have 160vdc, and so should pin3 which is connected to the mosfet drain., this is the primary. There is likely a low ohm resistor connected to THIS mosfet's source pin to hot ground.

[roadrash]

Re: Sorting out old PC power supplies?

I believe the mosfet you removed is for the main supply not the standby, the transistor for the standby circuit is near R905

Thanks RJ for that. That transistor is a smd one? I haven't replaced one of those yet but should manage it if I now what type it is and can find one.
Can i test it in place before changing it?

[goodpsusearch]

Re: Sorting out old PC power supplies?

The incandescent lamp in series would have saved one of the psus from blowing. You can google it and always connect it in series with the psu when you test psu like this in the future.

[goodpsusearch]

Re: Sorting out old PC power supplies?

It's not a cap, it's an MOV - completely different component.

As stj mention, sometimes they can also fail with time as they absorb high voltage spikes on the line.

If each of these is placed in parallel with the two 200V caps, then the new MOVs should have a rating of 180-220V. 180V may be a bit too low, though.

But again, these are not necessary,

chinese psu manufacturers would stop reading right here and press the like button

[R_J]

Re: Sorting out old PC power supplies?

I believe the mosfet you removed is for the main supply not the standby, the transistor for the standby circuit is near R905

[PeteS in CA]

Re: Sorting out old PC power supplies?

Thanks for that Pete, I think this is standard atx as I just compared its atx connector pinouts with a picture online and it shows one position empty which is the -5v line.
Here is a photo of thhe 20 pin connector. I have 6 of these desktops to fix the domed caps and ive done 4 of them and they are all working. This is one of the remaining 2 psu's' to fix.

The -5V location is empty, so it should be OK with a MB that doesn't use -5V and with your tester.

[petehall347]

Re: Sorting out old PC power supplies?

Brown
Green
Silver
Gold
0.15 ohms

[roadrash]

Re: Sorting out old PC power supplies?

it's wirewound - the fact that it meters low ohms means it's o.k.

I had a feeling it was that as its was mention a bit earlier about a low value resistor in that area. Why doesnt it match a resistor colour chart or was i reading wrong?

[stj]

Re: Sorting out old PC power supplies?

it's wirewound - the fact that it meters low ohms means it's o.k.

[roadrash]

Re: Sorting out old PC power supplies?

This redistor doesn't make sense.
Its colours are:

Brown
Green
Silver
Gold
White

I measure it at 0.76 ohms
But this combination of colours doesnt make sense on any 5 band calculator.

[roadrash]

Re: Sorting out old PC power supplies?

Thanks for that Pete, I think this is standard atx as I just compared its atx connector pinouts with a picture online and it shows one position empty which is the -5v line.
Here is a photo of thhe 20 pin connector. I have 6 of these desktops to fix the domed caps and ive done 4 of them and they are all working. This is one of the remaining 2 psu's' to fix.

[PeteS in CA]

Re: Sorting out old PC power supplies?

Your right I cannot see a -5v wire but there is a orange 3.3v one. Its not a apple.

If it has an orange wire in the -5V location in the 20- or 24-pin connector it is incompatible with MBs that use the standard ATX pin-out. The only computer company I've seen use that location for an extra 3.3V wire is Apple. Like I posted, I used to work for Delta Products. I was in tech support here in Silicon Valley, and Apple was one of the customers I supported, back in the late 1990s. That is when I saw Apple using the -5V location for an extra 3.3V wire. My current employer is also a computer company, and our 20- and 24-pin ATX connectors either have -5V in that location or the location is empty.

I dont get any DC voltage on 5VSB. I have a ATX PSU tester plugged into power cables so should be turned on. What precisely is the 384x you mentioned. Your dealing with a hard trying newb here remember.

The UC3842, UC3843, UC3844, and UC3845 are a series of 8-pin current-mode pulse width modulator ICs. Which specific part a company uses depends on the specific design. While I remember that Delta used parts from that series, I don't remember which part Delta most commonly used (possibly the 3845), so I substituted an "x" for the digit I could not recall.

Returning to my comments above, once you figure out the problem with the 5VSB circuit, if you have a 3.3V wire in the -5V location, the power supply is not compatible with your ATX PSU tester.

I'm pretty sure Delta used the Power Integrations regulators for their 5VSB circuit, possibly from this series, or this series, https://cdn.badcaps-static.com/pdfs/...2da99e9444.pdf . If you look at the sample circuit on page 8 of the first data sheet, look for components equivalent to R5, R3 & R8, C6, and VR2 and check them out. Those have to do with the the start-up and operation of the IC.

[roadrash]

Re: Sorting out old PC power supplies?

The standby +5v is likely supplied by the smaller transformer and it's primary is driven by a mosfet / single transistor circuit not by the 8 pin ic's
One pin of the transformer primary will be connected to the main cap +. The other pin of the primary connects to the mosfet Drain, and there should be a low ohm resistor from the fets source pin to hot ground (main cap -)

Thanks for that RJ.
I did try to see if I could get a connection between the Mosfet (drain and one of the connections on that small transformer but couldn't get anything. Anyway I removed the Mosfet (WN9K90Z) for testing and testing it with a multi-meter in diode mode, I got a open circuit between source and drain but if I touched the positive lead to gate to charge it the source and gate still remained open circuit which is not right. So I put my component tester on it and it correctly identified it as a Mosfet (see photo) so that must mean its OK I think.
Did anyone find a schematic for this PSU, I couldnt?