Desktop PC startup issue

[Harry Bloomfield]

My trusty old (6 years) desktop PC has been difficult to get to start for the past couple of years. I press the start button, the fans and HD's whirl, but no peep to prove it is booting. Leave it like that for a while, then force it to shutdown by pressing the button for ten seconds, once it is forced to shut down, press the start button again and it starts. Leave it for too long 'warming up' and it fails to peep and boot. Once started I dare not hibernate it, unless I don't intend to need it for several hours, because it would not restart. I can though successfully use a software restart for instance if new software needs the system to be restarted. Once running, it runs absolutely fine all day long.

As the weather becomes warmer, it becomes more tricky to get the 'warm up' period just right.

AS the PSU seemed the most likely issue I checked the PSU out when it was refusing to boot including the PG, everything seemed fine, but I tried another new PSU anyway, which made no difference - so I am now of the opinion that it is the motherboard causing the problem. To me, it seems to be thermally related.

I also tried adding a proper reset button, to the pins on the mb - that didn't help.

Today was one of those days when it refused to start, so I had another look at it. Guessing at the crystal failing to oscillate, I tried cooling that with a moistened finger tip and managed to get it to boot.

My PC motherboard knowledge is well out of date now, so maybe someone might be able to confirm I'm looking at the correct crystal for the motherboard + CPU etc.. I spotted two, one a familiar type used for the clock chip, the other is mounted direct to the PCB (no exposed leads), is very low with an oval top. Next to it is a surface mount IC and both are adjacent to the CPU socket. Close to both the above IC and the crystal there is lots of tiny (illegible) text. The crystal looks as if it is marked 148???? 148 Mhz(?). CPU is a dual 3Ghz.

I'm thinking to try replacing the crystal, after a bit more experimenting with cooling the crystal when it refuses to boot.

Resale value of PC = zero, but the effort of setting things up on a new system would be immense - so I would prefer to get this one fully working.

[Ivan Dobsky]

One thing that used to work often for me was just taking out the RAM and putting it back. If you're felling brave, clean the contacts a bit (I always do, but since they're supposed to static sensitive I'll advise caution). The contacts seem to oxidise a bit (I know gold isn't meant to), and become less conductive. Also works for auto bulbs too. I find they've hardly ever really blown. The soldered contacts just need a bit of a clean. Same principle, basically.

[Harry Bloomfield]

on 31/05/2013, Ivan Dobsky supposed :

I did a full strip down, contact clean and reseat when the problem first appeared - it made no difference.

I rub the lamp soldered contacts on a tyre BTW - very effective at cleaning them without damage.

[Ivan Dobsky]

Did you try just switching it on with mainboard, cpu, and speaker present? I think that's the minimum you'd need to get a beep.

Or how about applying pressure to the mainboard in various places. Like you may have done to locate a dry joint. That's what I'd suspect if it was temperature sensitive.

[Harry Bloomfield]

Ivan Dobsky explained on 31/05/2013 :

Yes, tried all of that..

If it were a dry joint, I would really expect it to cause issues once it had managed to fire itself up. As said my favourite culprit at the moment, is the main oscillator or crystal. I'll if cooling it helps tomorrow, if it refuses to start and it is warm.

[meow2222]

Prime suspect: failing capacitors. Get yourself an ESR meter.

NT

[Harry Bloomfield]

Funny you should mention ESR, I have one on its way from China, but no obvious signs of any failures that I could see and I twice done a visual.

[Ivan Dobsky]

Ah, well. I'm afraid I don't know you well enough to know what you already tried. I expect you know more about these things than I do, if you've already homed in on individual components.

However, I do know that it can be more satisfying to diagnose and fix something, than it is to just go out and replace it, and I hope you get there in the end.

[John Rumm]

Its sounds like this is a "not coming out of reset" cleanly problem. The most likely fault will be a failing capacitor somewhere in the power regulation/filtering circuitry on the board. This will mean either there is too much noise floating about on the reset line, or voltages are drifting out of spec / ripple tolerances etc.

Can you see any puffy / leaking electrolytic caps on the board?

If they are bad enough you can spot ones like:

I expect its more a case of your finger is adding a few puff of extra capacitance where required...

Why not just swap the motherboard and have an upgrade into the process?

[alan]

On an older motherboard the prime suspect may well be the battery. Check to see if there is a coin-cell fitted to the board, usually in a battery holder.

When the battery failed recently on my back-up computer of 10+ years vintage the boot cycle took 5 times longer.

[tony sayer]

In article , [e-mail] scribeth thus

Seconded. Have a careful look at the caps on the board if they look bulged or are showing signs of electrolyte leakage then thats most certainly the problem.

You can change them .. if you have the patience;!...

[Harry Bloomfield]

Yep, been there and done that lots of times.

[Harry Bloomfield]

John Rumm brought next idea :

Because it is a rather specialised setup - a standard MB will not go in.

[soup]

Opinion :-

I wouldn't faff about trying to troubleshoot and fix the old motherboard just replace (may require a phone call to MS to re validate the Win install [if you use one that is] but as the old MB failed you should get a new validation no problem).

If you cannot get a direct replacement for your old MB (need new RAM a new processor etc) may be time for a full upgrade anyway. Cloning the HDD will mean no changes to your software (building an entire system should take you no more than a couple of hours, more if you are videoing it, and less if you are skilled).