Strange behaviour of a mainboard

[Boncuk]

Hi,

I gave my stepdaughter her own PC a while ago.

This week the monitor turned black without any prior error message. The system also didn't reboot. I opened the case and found a lot of dust which I removed with a soft brush and a vacuum cleaner.

I also removed and cleaned the graphic acellerator card since there was a lot of dust on the PCI socket. I used methyl alcohol to clean the contacts and had the system start again successfully.

After one day the same thing happened again. So I removed the CPU and did the same procedure as with the graphic card. The system worked alright.

The day before yesterday she had again trouble starting the system. Not even the typical "beep" was to be heard after the RAM-walk. I was fed up and didn't try to "repair" that thing again.

Very much to my surprise the system worked alright yesterday when she returned from school and powered it up.

My guess is in the direction, that the mainboard is faulty not supplying the CPU core voltage properly at all times.

Air temperatures are presently moderate (between 27 and 34 deg/C), which leads me to the assumption that temperature can't be the issue.

Does anybody have similar experience?

Boncuk

 

[ericgibbs]

hi Hans,
I had the same problem recently on a desktop PC.
The display monitor remained blank after powering up. We traced it to the keyboard socket [PS2] which had dirty contacts.

As the PC was carrying out the POST tests it was checking the keyboard first, which it found to be 'faulty', so the system just hung up and did not show the expected 'error' message on the monitor.

We cleaned the PS2 connectors and now 99% of the time we get a good boot up.

The old PC had been stored in a barn.! so the PS2 contacts had become tarnished. [covered in s**t actually]

 

[transistor495]

My guess is in the direction, that the mainboard is faulty not supplying the CPU core voltage properly at all times.

I've experienced these kind of strange things before a number of times. I had a built-in HSP56 micro modem that won't be detected by the system if we use it normally. It'll get detected only if we keep the system idle for at least 1day or two, again it'll go off on reboot. I got mad needless to say.

You won't get any display if it's RAM failure. Yours seems like mainboard PS related issues. Just as a hint: try to replace the big el. caps on the board that may be got bulged. or probably supply regulater high freq. FETs/diodes on the motherboard failed -if so they'll allow the system to boot again only after cooled properly that'll take few hours.