windows desktop pc died - fixed

A few days ago my Windows 7 desktop computer died right in front of my eyes. These days I have gotten weary of repairing complex things. Repairing things get old after a life of doing everything myself.

Needing the desktop pc to do a number of time critical tasks I dived into it yesterday. I needed to create a generous flat surface so I cleared up a ton of paper work off my desk. Like the saying goes, sometimes when bad thing happens, there may be a silver lining. Guess what? Turning over the mountain of paper work on the desk I found the property tax which I totally forgot to pay. I panic thinking I must have lapsed to meet the deadline. Today is Nov 17th! Not too late if I just shake a leg.

I looked into pay online or pay by phone. You can pay either way with a credit card, but there is a catch. The 3rd party processing vendor slap on a 3% fee. I ain't stupid to give someone 3% easy money. I always pay in full to get the 3% discount the county gives and I am not about to give that up either. I called up the county office and confirm as long as I post mark by Nov 17th the check via snail mail to them I would be considered making the pay deadline. I drove to the post office and take the extra trouble to get the envelop post stamped by the clerk. Now home to fix the damn PC.

first task is to disconnect or remove all the at-risk components

I removed the power as well as the SATA connectors of all the hard drives and the DVD drive. I removed all the DDR3 DIMMs. I also removed the PCIe graphics card. The only thing that I need to debug is the motherboard, the system power supply, the CPU, and keyboard and mouse.

The system does not POST which means the CPU does not perform any code execution. I set out to conduct first level debug, hoping to isolate the faulty system level component. I re-seated the CPU in it's BGA socket. That isn't the cause.

Next step is to check the system power supply. I used a DMM to check all the voltage rails and did not find anything out of ordinary. At this point I didn't feel like bothering with an oscilloscope. I didn't want to check the system power supply off the suspect list just yet. The reason is it could be a power sequencing problem, or even a voltage regulation problem which a DMM cannot detect (e.g. excessive AC ripple).

I decided to swap in a known good power supply. For this I happen to have another desktop PC that has an identical power supply.

i built another desktop PC to used with Windows XP; i borrow the PSU to use as a known good reference

i bought these 2 identical PSUs  when they have a rebate; these are ATX-12V power supplies designed for the performance IA PCs

what do you know? POST code!

That was easy! The ATX-12V power supply failed. The noise I notice a few days ago before the PC died must be emitted by the power supply. For now I just want to get my desktop PC back in service. I carefully re-installed all the system components. Sorting out the SATA cables was a bit of chore as that matter. Not all the SATA ports have the same performance, in addition to the boot order. There are 4 SATA devices in this system.

all is good - i tested the system before putting it back to the normal location by the desk

even got to clean out all that dust bunnies behind the computer among the cable mess

When I have more time, I would dig into the bad ATX-12V power supply to see what is wrong. I would do that with an oscilloscope. I suspect one of the voltage rail has regulation problem, may due to a failure of an electrolytic capacitor. With luck I won't electrocute myself by high voltage AC or DC in the process.