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5-Minute Repair #004 - IanJohnston.com Web/Email Server PC

On the 7th March 2011 my web/email server fell to an early grave, the motherboard in the Shuttle PC decided it had finally had enough. The symtoms began weeks before with random re-booting and which progressed to being unable to boot into the bios let alone Windows, and finally to the motherboard firing up for less than 3 secs then shutting down. At this point it wasn't looking good for anything but the skip!

So, I pulled the backup hardware from storage got web & email for the family up & running again. However, I now had a situation where I was running without a backup solution, and since I couldn't get parts by way of a replacement MB for example for the knackered Shuttle it wasn't looking good!

To fully test, I did the usual and replaced the ram and checked all connections but to no avail and was about to chuck out the motherboard when I decided to strip it down for a closer inspection of the actual board. 20+ years of working in electronics has taught me a few lessons, one of which is that power supply's in particular are prone to breakdown and the reasons why!
Testing the PSU under load proved it was fine, so thoughts went over and a closer look at the actual power circuitry on the motherboard itself......and there lay the problem right in front of me.

If you look closely at the 2off large 6.3v 1800uF electrolytic capacitors in the photo below you'll see the tops of them are slightly domed. They should be completely flat and this a sure sign they have failed or at the very least are on their way out. It's a combination of time & heat which dries out the seals within the capacitor and failure. Luckily though no electrolyte has escaped which could have corroded the motherboard.
So, this explains the gradual demise of the server, over time the issue gets worse as the capacitors get drier and their capacity reduces further & further. The rest of the electrolytic capacitors on the motherboard looked fine.

 

Removed from the board the problem is easier to see.

 

Measuring the capacity on my cap. meter they are down from 1800uF to about 800uF each. Such a loss it's easy to imagine the motherboard failing to cope with heavy DC supply rippling as a result of less supply decoupling.

 

Here's a couple of new capacitors fitted. I didn't have the exact size physically/electrically in stock (sic!), so a couple of much larger 25v 2200uF electrolytics were squeezed in to the limited space available and with a spot of sealant to hold them. Not very neat to look at, but being for home use only.....who cares!
Notice the heat pipes from the CPU, they run right over the capacitors, so it got me to wondering if there was extra heat around there which contributed to the demise of the original ones, especially as this PC is on 24/7.

 

An here's the Shuttle PC back together and under test and in my new workshop! It's working perfectly including running a burn-in test CD I have. Job finished this Shuttle PC becomes the new 'emergency spare'.
UPDATE 01/06/11: Now running this PC as the live server for the hell of it.

PS: Note the 19" LCD is permanently mounted on the wall for just such PC repairs, and my mini keyboard/trackball combo which is great for a cluttered workbench.