POST failing intermittently

  faichfolds 22:25 07 Feb 03
Locked

Let me start by saying thanks for all the help I've had in the past!!
A friend of mines Tiny computer got zapped by lightning, and ceased to function. I had a look at it for him and the first thing I noted was the lead for the power switch was severed. I repaired that with a block connector, (as trying to find a replacement lead is like trying to find the proverbial needle!)
Hey presto now it works but only occaisionally.
The problem is it sometimes wont initiate the monitor, and there is no "beep" .
I believe it has IBM BIOS which no beep could indicate a short circuit. Any suggestions would be gratefully appreciated

  faichfolds 23:37 07 Feb 03

Could it be a graphic card fault?

  faichfolds 23:57 07 Feb 03

-

  faichfolds 01:25 08 Feb 03

...

  jazzypop 01:34 08 Feb 03

If a system got zapped by lightning, and sufficient current got through to melt a wire to the on/off switch, I'm surprised that it boots at all!

This is going to take a long time, starting at the PSU and working your way through. A good multimeter will be invaluable.

I suggest that you use this site - click here - it is thorough and comprehensive.

  faichfolds 01:37 08 Feb 03

Thanks for the link I shall read it at leisure.
What would your hunch be?

  oneMegaBit 01:42 08 Feb 03

you will be looking for the proverbial needle to solve this one. Any one of the components could be damaged. I suspect though, as jazzypop suggests that you start with the psu. It is more likely that there is an intermittent fault with this than a motherboard component, "chips" or ic's are so sensitive that if current had got to them they are likely to have been fried and the computer would not have worked at all, but although unlikely this is still possible. Happy hunting!

  jazzypop 01:43 08 Feb 03

If that amount of current went through the mobo, I would suspect that a lead from the PSU has had its internal insulation damaged, and two conductors are shorting - but that really is pure speculation.

Far better to start at one end, and work your way through methodically. Slow, but sure :)

Do check out all of the basic circuits and leads first, before you start substititing in known good components. If there is a damaged cable (possibly within the PSU itself), you risk damaging the 'good' component.

I would be inclined to see if a claim can be made under the household insurance for a replacement PC :)

  faichfolds 01:53 08 Feb 03

If the problem is in the PSU, that would stop it powering up the monitor wouldn't it?

  faichfolds 01:59 08 Feb 03

Sorry failed to mention that if you leave it in standby, ther is no problem

  jazzypop 02:02 08 Feb 03

If the monitor draws its power from the PC case, it *could* do - but so could many other things.

I'm sorry, but it is pretty fruitless trying to speculate and dive in on the most likely cause. From experience of many, many similar situations, I can honestly say that the fastest way to fix it is to start at one end and eliminate each possibility in a methodical way.

I can understand your desire to start with 'the most likely' - it almost never works :)

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