Sorting out old PC power supplies?
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Re: Sorting out old PC power supplies?
The point at which I suggest starting is whether or not you have 5VSB, the purple wire. If no 5VSB then that's where you start looking.
If you have 5VSB and grounding the PS-ON (green) wire doesn't turn on the main outputs then the PWM circuit is your starting point. Check the Vcc voltage on the 384x. If it's too low then there's probably a ~47uF cap that might be bad, or the resistor that charges it might be bad. Those provide the voltage to start up the 384x. One the PSU starts up the 384x Vcc usually is supplied by a bootstrap winding.Comment
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Re: Sorting out old PC power supplies?
i suspect it was 150v, although that may be too low for a 240v input.
maybe that's why it blew up.
total rectified voltage is going to be about 340v so divided by 2 it's 170v
so using parts rated between 200 and 250v is probably wise
btw, the psu will run without them - so if it's dead it probably blew the fuse or killed an input filter
VISHAY-EPCOS-METAL-OXIDE-VARISTOR-150v-QTY-5/123787501997
3-Metal-Oxide-Varistor-MOV-20D431K-275VAC-120/121769194537
Varistor-76-0J-300V-ac/391288103662?
Varistor-38-0J-250V-ac/391741394396?Comment
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Re: Sorting out old PC power supplies?
There two 8 pin chips in this thing but only one with 384 in its number. The one in this photo I hope.
I was unsure where to put the negative probe so put it on the "-" of the rectifier.
Doing this I didnt get any voltage reading.Comment
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Re: Sorting out old PC power supplies?
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 -)Last edited by R_J; 11-18-2020, 05:54 PM.Comment
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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 -)
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?Comment
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Re: Sorting out old PC power supplies?
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.PeteS in CA
Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
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To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
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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.Comment
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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
Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
****************************
To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
****************************Comment
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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,Comment
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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.Comment
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Re: Sorting out old PC power supplies?
Can i test it in place before changing it?Comment
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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.Last edited by R_J; 11-22-2020, 04:24 PM.Comment
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