Eliminate Motherboard vs CPU

Does anyone know of any definitive way of eliminating either the motherboard or CPU when troubleshooting a no-post no-video desktop? Also no keyboard flash during postup attempt?

I have an HP Pavilion a220n that spins up with the front power switch (CPU fan and hard drive), but no beeps, no video, no other signs of post. I tested power supply voltages while under load (all checking out within spec), stripped it down, substituted RAM, and still got same result. I ordered a replacement motherboard, and (arghh!) it does the same thing. I substituted the power supply, same result. Now I have ordered a replacement Athlon 2600 processor. I don't usually suspect the CPU, they are usually fairly robust, and I am somewhat afraid that it won't change anything.

I worked for an HP field service company awhile back, and encountered this same issue once. The phone tech said he was going to send out yet another new motherboard and power supply, thinking that the first new motherboard they sent out was taken out by the PSU, even though I felt the voltages were all in spec. They didn't suspect the CPU. I never got the followup call on that particular customer to find out if that really fixed the problem. With gas prices being what they are, and the great distances they had me running, I decided to quit for what they were paying me. Now I guess it's my fate to find out the answer on my own machine. I inherited it because the customer bailed out when they saw how much the proprietary parts are, and they had the machine stripped of anything valuable and installed on another unit. Then they said pitch it in a dumpster. I must admit I'm getting tempted. Anyway, it's my headache now for sure.

I would like to get this unit up and running as a test box in the shop (I could never sell it now and break even), and I just shelled out a lot of money on the motherboard from HP Parts. I made very sure of those PSU voltages before putting it in. I must admit this one has me a bit spooked, but at least it is my own to worry about and not a customers.

To get back to the topic of this thread: I never quite know once I feel it's either the motherboard or the CPU, and not having a good known working CPU to test with, how to really make that last decision: Is it the mobo or the processor? I usually just go with the odds, which in my experience is that it is the motherboard much more often than the CPU, but usually I don't have such a horendous proprietary cost on the motherboard. The CPU, BTW, had no visible signs of overheating or anything. Just my luck that when it cost the moon, it turned out not to be the motherboard. Anyone know of a good way to do this without having a CPU on hand to sub in?

Well, you've pretty much summed it up already, but here's what I would do:

I would try another CPU if one is available (usually I can get ahold of one somewhere). If I couldn't find a CPU to try, I would assume it to be the board, unless I found any signs of overheating on the old CPU, OR a bad fan on the old CPU.

Other than that, it's a game of toss up, and my money would be on the board every time - gotta stick with the odds!

Usually when a CPU dies it will show some sort of damage on the packaging. My money is on the motherboard too.

Looks like you do this professionally, so I would bite the bullet and buy an Ultra-X P.H.D. PCI 2. It has onboard video, RAM, and it will boot from its onboard ROM with no OS and can test boards that most POST cards just report as dead. I have one as well as POST cards from 3 competitors, and there just isn't any comparison. Over the long run it will definitely pay for itself.

Ultra-X makes some really good stuff for diagnosing hardware. I have been using QuickTech for 8 years now. It's pretty good about finding problems with systems that will POST.

Thanks for all your help on this, especially the tips on diagnostic aids. It nice to know when you are out in the wilderness with the wolves howling outside your door that guys like you are out there ready to share a good word :thumbs: