PG (+5v) from PSU is not present when all other voltages appear and are within tolerance. How?

[kyjohnnyb]

My Gateway FX530S, an older ATX, will not usually boot at all. Before I began to work on it, I tried it one last time (it had been in storage for 3 mo). Surprisingly, it went through all or a significant part of the boot-up before locking up. However, most of the time before the three months it simply gave me a black screen and I could hear the fans and hard drive running but nothing else. Prior to its complete failure, it shut off two or three times after making it into Windows and executing some programs. The final time it came on and actually got to Windows, it died almost immediately. After this, I got black screens and had to put in storage. I did check to see if the monitor was good. It was.

So I bought a PSU tester (led kind) and a dmm. I unplugged all the connections of the PSU and plugged a mobo tester to the 24 pin connection. Every led came on except -5v (which I came to understand is outdated and may not be present) and the PG led was definitely off. I confirmed by testing the PSU's mobo plug with a dmm. All the voltages indicated by the mobo tester were present and seemed within tolerance BUT still no 5v signal on the PG wire. What gives? How can this be?

 

[Lutfij]

Depending on which PSU tester you're talking about there is s specific order and manner in which you connect the PSU leads to the plugs on the tester. One thing to note is the PSU tester in no shape manner or form indicates that a PSU can operate at a certain load since you'll learn that in order to power a PSU with nothing connected except a paper clip(paper clip test) you'll need at least a fan to simulate load on one of the rails. This, mind you, does not ensure that the PSU can operate at, say, 50-80% load which is what you're seeing with your unit when a load of perhaps greater or equal to PSU's output is taking place.

last point to make, get a reliable unit for your units, prebuilt branded units apparently have non branded unreliable units stowed away in their chassis and yet are charged for higher due tot eh chassis' brand logo/badge.

 

[GhislainG]

A good explanation of power good: http://www.pcguide.com/ref/power/sup/funcPowerGood-c.html If the PSU doesn't supply it, then it has an issue and it should be replaced.