PSU shuts off or makes weird sound and won't boot

[Pentium4]

When this PSU is plugged in, it will power on for about 10 seconds and then shut off. After that, it will make a short, weird "zzzzt" sound when attempting to power on but believe it or not doesn't sound like something frying....sounds more like a buzzer. It will not power on until unplugged but always gets a stable 5.00V 5VSB. It has plenty of load on all rails.

Here is what it looked like originally: https://www.badcaps.net/forum/showpo...&postcount=646

What I did: I replaced the fake input caps with 680uF (tested good), replaced the regular ceramic discs located in CY1/CY2/CY3 with real Y caps from a scrapped monitor power board (Didn't test them though....) added an input coil from an SP450, recapped the entire thing with good caps. I replaced the secondary heatsink with a bigger one but kept the original rectifiers (I did slightly bend 2 of the rectifier legs to fit properly) The heatsink has no grounded leads, it's just sitting on the rectifiers but isn't touching anything. I originally had the minimum load resistor on the 5V rail removed, added it back and it's still having the same problem. I also took those rings off the 2 Y caps to no avail.

One of the leads on the bridge rectifier lost some of its pad, but I figured if it was a major issue this thing wouldn't get standby or power on at all.

I would love any feedback or input from you experts, thank you for your time!

Added pics of what it looks like after I modified it

[cheapie]

Re: PSU shuts off or makes weird sound and won't boot

Are all of the voltages normal while it's running? Is the controller or protection IC (if present) losing Vcc? Do any readings on any of the controller's pins change just before it shuts off? That Rubycon(?) by the +12V wires looks funny too (in the first picture, anyway).

[Pentium4]

Re: PSU shuts off or makes weird sound and won't boot

I haven't checked the IC's voltage, but all of the main rail voltages test good while it is running

[ben7]

Re: PSU shuts off or makes weird sound and won't boot

Tested the computer with a different power supply?!

[Pentium4]

Re: PSU shuts off or makes weird sound and won't boot

Tested the computer with a different power supply?!

Yeah, and I've tried a different setup as well

[ben7]

Re: PSU shuts off or makes weird sound and won't boot

Yeah, and I've tried a different setup as well

So it does this with load and without load?

Seems like something is triggering low voltage dropout - could be one of the control chips not getting the right power.

[Pentium4]

Re: PSU shuts off or makes weird sound and won't boot

I haven't tried it without a load yet, so I will try that. Could a shorted part on the input filtering cause this?

[ben7]

Re: PSU shuts off or makes weird sound and won't boot

I haven't tried it without a load yet, so I will try that. Could a shorted part on the input filtering cause this?

I don't know, but have you checked the voltages across the primary capacitors? You know, they are Meta-Trash!

[goontron]

Re: PSU shuts off or makes weird sound and won't boot

need pics of the bottom of the board to

[c_hegge]

Re: PSU shuts off or makes weird sound and won't boot

Shorted input filtering would just blow the fuse

[Pentium4]

Re: PSU shuts off or makes weird sound and won't boot

I haven't checked the voltage across the primary caps. I will get a solder shot soon...When using the paperclip trick, it doesn't shut off and all the voltages are in good ranges

[cheapie]

Re: PSU shuts off or makes weird sound and won't boot

I haven't checked the voltage across the primary caps. I will get a solder shot soon...When using the paperclip trick, it doesn't shut off and all the voltages are in good ranges

Then you almost certainly aren't getting PWR_OK. Do you get 2.5V or higher on the gray wire when the supply is running?

[Pentium4]

Re: PSU shuts off or makes weird sound and won't boot

Even though it will power up for 10 seconds? I will check on Monday!

[Pentium4]

Re: PSU shuts off or makes weird sound and won't boot

The Power Good wire gets 5.16V when the PSU is running using the paper clip

[Calchaqui]

Re: PSU shuts off or makes weird sound and won't boot

What did that buzzer noise?

[Pentium4]

Re: PSU shuts off or makes weird sound and won't boot

Not sure...but it was a solder bridge causing a short, forgot to take a pic....I also thought it was a waste to have an 8A bridge in there so I took it out and replaced it with 4 diodes