Ot - computer won't boot

[J. L.]

On 18.03.2017 01:26, Gene Heskett wrote:
> On Friday 17 March 2017 19:54:56 Phil wrote:
> 
>> Thank you for reading this and I know that this a vague  question but
>> you may be able to give me a lead. For the past  couple of days my
>> desktop computer has been very slow to begin the boot process, perhaps
>> 5 minutes or so. Now it won't boot all. The disk activity led blinks
>> at about a 3 second rate, the fans run, and speed up once the system
>> warms, and I can measure 5 and 12 volts at the disk drive. There is no
>> video from the on-board video chip (which is normal until the system
>> boots up) and the system won't boot from the cd drive either. I've
>> reseated various connecters and the ram board. So, the power supply
>> and disk drive are propably ok which leaves the mother board, ram and
>> cpu but how I determine which one is at fault? I'm at least a 1000km
>> from civilisation so I cannot speak to service personnel.
>>
>> Sent from Samsung tablet.
>> Regards,
>> Phil
> 
> This isn't much to go on, but as a C.E.T., I'd be looking at the tops of 
> the electrolytic caps on the mainboard, particularly those right near 
> the cpu socket, looking for bulged or even open cracks in the safety 
> scratches in the aluminum on top of them. I'd also open the psu and look 
> at the caps in it, again looking for bulged or vented tops. This would 
> be a sign of the capacitor in a switching circuit, and these all are, of 
> excessive ESR, Equivalent Series Resistance.  PSU's of more recent 
> history than 10 years, seem to have a built in voltage fade with time, 
> and the 5 volt line, if below 4.75 to 4.8 volts when first turned on, 
> will hold the cpu in reset until the voltage gets above 4.8 as these 
> caps warm up, but eventually the ESR causes so much heating they will 
> vent and its game over.
> 
> What you do next depends on the soldering tools you have, and a src of 
> spare capacitors to install. Lacking those, you may well be out that 
> 1000km drive back to civilization to just upgrade to fresh stuff. Even 
> with a hot air rework station, its hard to change the motherboard caps 
> because the pattern on the board is big and fat so it can serve as 
> additional cooling heat sinks for the caps, so you really have to turn 
> up the heat and potentially cook the board just to get the old ones out.
> 
> Thats my best shot at it, based on 65 years of chasing electrons to make 
> them do usefull work.  Best of luck guy.
> 
> Cheers, Gene Heskett


Well, there's not very much i could really _add_ to this post as several
years ago i had a system with exactly the same problems (booting only
after several (sometimes even more than 10 to 15) minutes after
"power-up") the OP has described. And finally i found out that the caps
on this board had slowly been ageing and finally dying.

+1