Troubleshooting Power Problems

Recently I have had several friends bring me computers that will not power up. I am by no means a computer repair professional, but do it as a hobby on the side. My problem is that I do not have a lot of spare parts to troubleshoot with so I am seeking advice.

From what I understand, if you are not getting power at all it could be one of four things. Power Supply, Motherboard, CPU, or Memory. I am going to assume that the power button for the case could also go bad?

I do have a Power supply tester from Frozen CPU.com that is the virtual hideout edition. I unplugged all power connections from the motherboard except the 24 pin and tested the psu. I get all lights (+5v, +12v, +5VSB, PG, -12V, and +3.3V)

The only light I do not get is the -5V. I thought maybe the power supply was bad because of this until I read on the Frozen CPU website

"Note: Newer 24-pin power supplies often do not supply the -5V line anymore since it is no longer needed by modern motherboards. If your power supply tester's -5V LED doesn't light up with a 24-pin power supply, it is not an error. The power supply is functioning properly."

This first system I am working on is a HP Pavilion a1630n that is about 3 years old. My friend took it to Best Buy first and they tried a new power supply which did not fix the problem. They said they thought it was the mobo, but I do not know if they tried new memory or cpu in it.

I am going to try unplugging one stick of memory at a time and also switch slots around to see if I can rule out the ram. Any other troubleshooting advice? If it is mobo or cpu I doubt I can find the same parts to replace and would advise friend to start looking at new computer.

Thoughts?

 

Power supply, yes. A bad motherboard might (depending on the actual fault) prevent a PSU from powering up. But no power at all is not caused by the CPU or RAM. If the CPU or RAM are bad, the system will attempt to power up, but then fail. I too use a frozen PC PSU tester when I am "in the field" but they are no substitute for a professional checkup by a qualified technician. So often the best solution for home users is to swap in a known good supply.

Do not worry about -5V - as noted, it is not used today.

I have NEVER seen the power button on an ATX case fail. These are not "power buttons" like the old AT cases and AT power supplies. They are simply simple "momentary contact" switches that short two pins on the motherboard signaling the PSU to fire up. They are very low tech, and not subjected to high current, or physical abuse. To test the switch, carefully short the two pins and see what happens.

Using one stick of RAM at a time is a good start (after verifying good power), just be careful to keep yourself at the same potential as the case by touching bare metal before reaching in, and frequently thereafter. And don't forget to unplug from the wall before removing or installing any hardware. Swapping slots may or may not help, depending on the motherboard. I would visit each computer maker's website and download the user manuals before starting to see how the memory can be installed.

You could probably find a replacement CPU, but they may be costly. Exact replacement motherboards would be very difficult.

Do not try to troubleshoot all computers at the same time. It is not likely they have the exact same hardware, software, configuration, or fault.