Power Supply Troubleshooting?

I have two older desktop machines which worked the last time I used them.

One has been unhooked up and now will not power up. Do power supplies fail when not in use?

I have another machine that worked at the beginning of the year, and has been on a little-used desk in my apartment, off, but fully-assembled. There is a light in the back of the machine near the power cord, and an LED on the motherboard which is lit yellow. (photo included below)

This machine also has a power switch button on the front of the case which is unresponsive.
Does anyone have any idea what I'm dealing with here, or how to diagnose the reason it won't turn on?

There are no fans running.

Thank you.
d

 

Is it correct to assume that if the fan on the PSU is not working, that unit itself has failed, regardless of lights?

 

Yes, it is possible a PSU (or any electronics) will not start after long periods of non-use. But there is no set reason why. It can just be a coincidence.

No. If the PSU is not getting the proper signal to come out of stand by mode, the fans will not spin but the supply could still be good.

Make sure the master power switch on the back (if they have one) of these power supplies is in the on (1) position. All PC power supplies automatically enter standby mode when simply plugged in and the master power switch is set to on. If no switch, they go into standby mode anyway.

It might be good to invest in a PSU Tester. When these devices are connected, they short out the two pins that signal the PSU to start up. They also apply a small but sufficient load on the PSU to test if the PSU can produce the 3 necessary voltages (+3.3VDC, +5VDC, and +12VDC) for the computer to start. These testers are not conclusive because they don't test for ripple and don't apply a variety of expected loads. But if the PSU does not start when connected to one of these testers, the PSU is bad.

 

You could borrow one psu from a friend testing if it works or not in your machine , in another case Digerati suggestion is only solution for you , also you could open up your machine case checking all components like cables , reseated ram etc , maybe bios battery is the culprit , removing and reseating it as well

 

The CMOS batteries could certainly be dead but a dead CMOS battery will not prevent a PSU from turning on. Typically the computer will still boot but the date and time will be off, drives not properly recognize, it fails POST and more. The point being, the PSU still turns on the computer tries to boot.

And certainly an internal visual inspection would not hurt, but I note one of the computers has been sitting quietly on a desk - not tossed in some storage room or basement corner.

Swapping in a known good PSU is typically my first suggestion when troubleshooting HW issues and is a good one here. I didn't mention it because we have two computers that did work and suddenly don't with the same symptoms. Could be both supplies failed at the same time, but that was sure be some coincidence.

 

I have had laptops with totally dead cmos batteries, and no way would they boot up. It might depend on just how long they have been stored, and when last used- Cmos batteries are so cheap, always worth trying, as a first step. But, as Digerati says, the psu substitution is worth a go.

 

This is an interesting piece of hardware, and I think I may go ahead and get one. I have a third machine we're woring on in another thread.
http://forums.majorgeeks.com/index....unexpectedly-and-now-wont-start.313803/page-3

The symptoms lead those helping me to recommend a clean install, and in doing so, I've found issues with my graphics card. The question were trying to solve there is whether or not the card itself failed, or if instead the power to the PCiE bus is insufficient. That is why I went to these machines - to try and install the card and verify. (as of Reply #128 from Satrow)

It looks like this PSU Tester will address several of my issues, if I am understanding the product info properly from the link you provided? If so, then I will definitely order one.

 

This is what I thought I knew, but I also note that Baklogic is disputing this claim. He is also referring to laptops, though, while these are desktop models.

I will try re-seating things in the one that's been assembled but idle. I did include a detail photo of the board with a lit LED indicator in the OP.

I have yet another older unit that ran XP in storage nearby, and maybe even a harvested PSU, come to think of it. I guess I assumed that those units would have varying specs based on the particular machine specs. I'll take some time and inspect them carefully, and report back.

 

I have never needed to replace a CMOS battery, but it looks straightforward. Can I get them over the counter anywhere, or best to mail order? Are they all the same standard size, or do they vary? Do you know? I can always inspect each unit, but my eyesight is poor for those small inscriptions.

 

And you are correct. PCs are not the same as laptops. And booting up is not the same thing as the PC power supply not even starting.

 

Unplug the power and hit the power button, then hook the power back up & hit the button.
Also you can test the supply by jumping 2 pins..
http://www.howtogeek.com/172933/how-can-i-test-my-computers-power-supply/

 

Sorry about that post, the brouser froze on me twice, and I had to save from my frozen screen