motherboard reserection....

[Silicon Skum]

Hey folkes, been a while - though I'd share this little tale with you.

So, my computer died a few days ago, well actually it caught fire (as in flames and smoke!), it was lucky that I was still awake at 3am when it caught fire (I nearly gave up and went to bed......that choice could have had a NASTY result....... ), I trying to work out why it was going unstable randomly, yet work for days at a time rock solid, before taking a dump again. This had been happening for a few weeks.

Well, as it turns out the instability was partly due to a VRM capacitor bloating up and blowing it's guts out (acidic...nice! ), though to be honest, I don't think it made TOO much difference as the system was still able to operate stable for days at a time. The REAL cause of the problems - and the fire - was due to the ATX connector on the motherboard overheating on the +5v lines, ALL 4 OF THEM! They were charred to buggery, and the ATX connector block and plug were welded together. The +5v wires going to the plug were turned from the normal red coloured plastic coating, to a black, crispy, brittle one.
The fire was caused by a build up of dust and fluff around the ATX block (which is hiddedn partly behind my hardrives, so rarely gets cleaned out properly). The +5v lines must have been failing one by one until only one or two were still able to supply power to the board, this meant a hell of a lot of current was going through the remaining wire(s) - enough that it got hot enough to cause the plastic of the ATX connector / plug to catch fire and in turn ignite the fluff inside the case.

So, I striped the computer down to assess the damage, figured I could still fix the motherboard if I replaced all the damaged components (ATX block, PSU ATX plug / wires, a number of capacitors that had been burnt, a questionable VRM chip that looked like it had been VERY hot for some time (proly caused by the faulty VRM cap causing the regulator to increase switching speed), and one of two other bits that needed attention).
Lucky for me I have a box full of old / broken computer parts, so I scavanged an old dead motherboard for parts. Most parts were suitable for replacement, the VRM was a suitable spec for a replacement - a little off but close enough, but some of the caps were well out of tollerance so I had improvise by adding pairs in parallel to get the capacitance as close as possible. Sadly I was one cap too short, so the cap on the VRM is running 1100uf under spec (should be 3300uf, using a 2200uf), so my VRM is switching somewhat outside the motherboard design specs, so will be a little hotter than normal, but should not be a problem, stability or voltage wise.

It's taken me nearly two days to get the motherboard repaired, Soldering on multilayer PCBs is a PAIN! I had to re-do some othe the repairs a day later due to a couple of bad solder joints that had not flowed into the "through board" solder holes (this is why I hate multi layer PCBs!) and the initial replacement capacitor I used for the VRM (the correct value too) turned out to be a dud, which then swelled up ready to pop it's guts (I checked the cap spec, turns out it's on the list of faulty "plague" caps - BOLLOCKS!! ).

So now the system is running stable and all is well, in fact I'm using the computer to type this post. It does smell a bit of burnt circuit boards though.

You may be wondering why I bothered to fix the board, well I just don't have the time or the spare cash to build a new computer right now, and besides - I'M A TWEAKER!! I have plans for a replacement, but thats on hold for at least a few weeks until I have some spare time (and hopefuly some money in my bank account - had to spend many thousands recently on my rental properties).

SS
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my sig disappeared from the image host (?)
But at least I have a Josh Award!

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