[time-nuts] 5070B once more.... (actually capacitors)

[Stanley Reynolds]

I've done the repair pulling the caps off the board leaving the leads which is what I solder too, not petty but no need to remove the motherboard. May need to clean up the leads if some aluminum foil is left behind. Also add hot glue for support under and around the new capacitor. 

Stanley



----- Original Message ----
From: Magnus Danielson <magnus at rubidium.dyndns.org>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Sent: Saturday, May 23, 2009 6:45:10 PM
Subject: Re: [time-nuts] 5070B once more.... (actually capacitors)

Tom Clifton skrev:
> The word we got from our Dell National Accounts rep was that there was a run of contaminated electrolyte affectring several capacitor manufactures. Gee, go figure QC issues in a country still painting toys with lead based paint...
> 
> Any way, I recently purchased a pile of low ESR caps from Mouser to fix five machines from the junk pile at work to build more linux utility boxes.  (perhaps $40) Turned out being a lot harder than I had anticipated as the internal ground planes on the Dell Motherboards made the old caps dogs to remove, and the new ones very hard to solder back in without cold joints.
> 
> After the first one, I returned the others to the pile and picked up other machines with good motherboards and bad hard drives or power supplies to get the rest of the machines I needed.
> 
> Guess I failed rework-101...

You need to use a hot-air gun to pre-heat the whole PCB. By doing that the heat-flow will be less as there is less of a temperature gradient.
The board needs to be made fairly hot... but after doing that, it is not as hard to unsolder them, clean the holes and then solder the new caps in.

Cheers,
Magnus

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