powersupplyWhen it comes to hard repairs, power supplies are the easiest things to replace, but sometimes that hardest to troubleshoot. Most testers only measure the voltages – with minimal load. So a number of problems aren’t caught. But it’s still basically a two step process. Power up on the tester and ensure all voltages are within spec. Then toss in a new or known good working supply and see if the problem (usually the system not power up) goes away.

Easy right?

Well we encountered one of the odder power supply issues we’ve seen in awhile. HP Pavilion desktop that the user said would sometimes boot, other times it would hang on the BIOS screen. When we powered up the system, it booted fine. We ran some virus scans, then rebooted and it hung at the BIOS screen. Multiple hard resets later, it was hanging or it was booting and when it would hang, it wasn’t always at the same point. Bizarre.

Tested out the memory and hard drive. Working great. Checked the motherboard capacitors, since this system was a few years old when that was a problem. They were fine. But that reminded me that systems with blown capacitors could sometimes act very similar  and unstable. So for kicks we swapped out the power supply and sure enough – system was rock solid. Clearly one of the rails was not stable and was causing the system to not boot even though it would always power up.

So if you have a computer that’s behaving strangely – it certainly could be the CPU or motherboard, but don’t overlook that a power supply that seems to be working fine, could be the culprit.