StrongARM CPU refurbish

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sP1d3r
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StrongARM CPU refurbish

Post by sP1d3r »

I've had to refurbish my SA-110 cpu because I checked the 4 10uf 16V electrolytic capacitors and found that the two nearest the voltage regulators were well out of spec.

Although the esr was high, the capacitors didn't look like they were leaking and because the CPU card is quite dense in terms of component placement, I thought that I'd try an alternative method of removal than applying a suitable bit of desoldering wick to the pads and then lifting one side at a time with a soldering iron (no smd tweezers!).

The easiest way of removing a difficult surface mount capacitor is to use a thin sharp blade to cut the legs where they come out of the can, but if you slip with the blade you could easily damage nearby components or tracks or open up your fingers, so care is required.

The pictures show how I did this, it's easy enough if you aren't in hurry. I mostly try repairing old computers because I find it therapeutic, bear in mind that I don't mind taking all day if it works suitably. I then soldered on two new capacitors and the CPU now works fine.

\:D/
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dominicbeesley
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Re: StrongARM CPU refurbish

Post by dominicbeesley »

Good work. Is this something that is common. I have a StrongArm machine that was unreliable last time i tried it 5 years or so ago.... since then the battery had leaked so i need to do a full restoration. I will check the caps!
sP1d3r
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Re: StrongARM CPU refurbish

Post by sP1d3r »

dominicbeesley wrote:
Sun Jul 12, 2020 6:38 pm
Good work. Is this something that is common. I have a StrongArm machine that was unreliable last time i tried it 5 years or so ago.... since then the battery had leaked so i need to do a full restoration. I will check the caps!
Hope that you can fix it.

I think that with capacitors that are designed into circuits because they've some resistance in comparison to components with negligible Esr, the effect of electrolyte deterioration upon the active voltages in the circuits probably leads to stress on voltage regulating components.

This'd make refurbishing a necessity if you plan to use the computer for more than as an actual computer as opposed to an emulator.

I don't use the computers that I own much but I don't want them breaking down because I've not bothered to check if they're in gwo.
soviet
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Re: StrongARM CPU refurbish

Post by soviet »

Found out that the easy way to get the caps out is use pliers hold the cap and then twist the cap this will rip the plastic part and the top.
Then use the solder wick to remove the legs.
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danielj
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Re: StrongARM CPU refurbish

Post by danielj »

And, if electrolyte has eaten away at the board or the adhesion between copper/board isn't strong enough, you'll rip the capacitor pads off. Not a sensible recommendation. It should be very clear that people using that method to potentially risk a much more extensive repair.
dominicbeesley
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Re: StrongARM CPU refurbish

Post by dominicbeesley »

Thanks. I've got a reasonable array of rework gear. Twisting of does have its place for electolytics but only as a last resort. I didn't think rpc motherboards were particularly prone to pads lifting. I'll probably just hot air them with suitable sheilding
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myelin
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Re: StrongARM CPU refurbish

Post by myelin »

The best trick I've seen for safely-but-destructively removing caps like that is to cut through the can with a pair of side cutters, pull off the plastic spacer, then desolder the two leftover pins. No undue forces on the PCB pads, and plenty of access so you can desolder the pins one by one. I saw it in a YouTube video somewhere, and it worked well on the A5000 (which was so badly corroded that tracks were rusting under the silkscreen).
SW/EE from New Zealand, now in Mountain View, CA, making BBC/Electron hardware projects for fun.
Most interesting: Arcflash, FX2+PiTubeDirect Tube/Cartridge adapter, USB cart interface.
markdryan
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Re: StrongARM CPU refurbish

Post by markdryan »

myelin wrote:
Tue Jul 14, 2020 12:45 am
I saw it in a YouTube video somewhere, and it worked well on the A5000 (which was so badly corroded that tracks were rusting under the silkscreen).
This one perhaps https://www.youtube.com/watch?v=rEhYVyXYU9c? I tried this on my A7000 and it also worked well, although my attempts to solder a new capacitor weren't such a shining success.
sP1d3r
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Re: StrongARM CPU refurbish

Post by sP1d3r »

myelin wrote:
Tue Jul 14, 2020 12:45 am
The best trick I've seen for safely-but-destructively removing caps like that is to cut through the can with a pair of side cutters, pull off the plastic spacer, then desolder the two leftover pins. No undue forces on the PCB pads, and plenty of access so you can desolder the pins one by one. I saw it in a YouTube video somewhere, and it worked well on the A5000 (which was so badly corroded that tracks were rusting under the silkscreen).
Ok if you don't stress the solder pads when you're cutting the capacitor.
:-s
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