Question Pc powering on issues

[Hanleyjaa]

I have this old hp pavilion desktop that i use for different projects, and actually a while ago while I had it running as a webserver one day i tried to ssh into the server, saw that it couldn't connect then realized the server was down so i opened the side of the case while it was on, and the case fans were spinning but not the CPU fan.

so i powered off the system and stored it away because i didn't want to deal with it at the time. but ive since tried to fix the issue but to no avail. when you power on the system the CPU fan starts spinning for a sec then stops while all other fans continue to spin until you power off the system. I then hooked it up to a monitor and it won't post, or show any video output. whats ur thoughts on the problem? is the issue the cpu fan? if it is, wouldn't the computer still post?

 

[Grobe]

Most likely the motherboard are going defect by old age.

Try to see if all capacitors looks good - if you can visible see that there have being over-pressure because top lid aren't flat, then you have it.

 

[Hanleyjaa]

Most likely the motherboard are going defect by old age.

Try to see if all capacitors looks good - if you can visible see that there have being over-pressure because top lid aren't flat, then you have it.

i did some more diagnosing on it, and removed a ram from slot one and tried turning it on, which didn't work so i seated the first stick back then took out the second stick of ram, and it posts, it shows the correct CPU configuration, along with correct ram amount, but it says "511-CPU fan not detected" would this be a problem with the actual fan, or the fan header? when system first receives power the CPU fan will spin up then abruptly stop while other fans continue to spin.

 

[Grobe]

So you removed one RAM stick, and now you're able to boot, but the CPU fan doesn't run?

Does it start to run if you attempt to boot an OS ?

Have you checked the bios settings for:

• Settings that make the CPU fan to run only under specific conditions (i.e. temperature threshold) ?
• CMOS battery voltage ?

 

[Hanleyjaa]

So you removed one RAM stick, and now you're able to boot, but the CPU fan doesn't run?

Does it start to run if you attempt to boot an OS ?

Have you checked the bios settings for:

• Settings that make the CPU fan to run only under specific conditions (i.e. temperature threshold) ?
• CMOS battery voltage ?

sorry it took me a while to respond back, but ive since fixed the issue. it posted but if the CPU fan, the one on the heatsink was plugged into the CPU fan header(4 pins) then when it posts it will stop you and say "511-cpu fan not detected" but allows you to boot into the OS which i did, i had alot of updates to run because it has been offline for months and months, and as the CPU was reaching 100% cpu usage the CPU fan would not turn on, so i used a desk fan to cool the CPU while i did updates lmao.

But heres where it gets confusing, i wanted to see if the CPU fan header or the CPU fan was dead so i unplugged the CPU fan and unplugged one of the case fans and swapped their connectors so the case fan is connected to the CPU fan header and the CPU fan is connected to the 3 pin fan header, then i turned the PC on and to my suprise the CPU fan AND the case fan were spinning and working perfectly, i then swapped them back to see if it would work now, and it didn't the CPU fan will not spin if its on the 4 pin CPU fan header. do u know why this is happening?

 

[Grobe]

I can only guess that one fan controller is trying to do a fancy soft-start or something, and maybe a self-check reveals that the fans doesn't respond.

Or it can simply be one of the fans have faulty feedback - you can check this by looking at fan speed from within bios menu.