exxos's Atari, Amiga & retro forum

Hi guys n gals,

I'm currently testing an SGI Indigo2 PSU 'PEC4074'. I didn't want to just put it into a machine and hope it works so I've been bench testing it. This is a 'ground to stop' PSU which should just turn on when AC is supplied and there is some loading on the rails.

• It doesn't turn on when turning AC on
• Tried using my load resistors & also a HDD on the molex
• measured pin 5 (5v standby) which should always supply 5v even when off, it was only 0.15v.
• when turning the AC off, the 5vSB voltage slowly discharges to 0 while making an audible spiralling deceleration high pitch noise.

I'm not a PSU expert and my method of fixing PSUs is usually a shotgun approach. I'm hoping there may be someone in this forum who is good with PSUs and may look at it for me. Happy to pay for time or with my own labour if you need jobs done.

Valuable info on this PSU, non impact model:
https://forums.sgi.sh/index.php?threads ... asics.111/

Here are some photos:

Apply +5V to power good pin to make it start up?

EDIT: Sorry. I was thinking the wrong way around. It's the PSU that gives 5V on that pin when all voltages are good.

It's supposed to auto-start as it is a 'ground to stop' and the SB is supposed to be 5v during idle... you think I can just ignore all that and try?

Ignore my input, I just edit my first post.

It's ok @DoG I tried that just a moment ago, but it didn't make any difference :(