Re: Corrosion abatement

All right. Soaking is underway in a 50/50 mixture of distilled white vinegar and water.

Participating in the soak are the I/O board, the motherboard, and the lower inch or so of both RAM boards, where a little corrosion is evident on the edge connector and on the leads of electrolytic capacitors C96 and C97. Surprisingly, the CPU board shows no corrosion at all. The COPS 421 chip is soaking alongside the I/O board, since a bit of corrosion was apparent on pin 24. The other socketed chips are removed

I am using disposable aluminum roasting pans for the immersion. I was a little concerned that all of these different kinds of metals in a slightly acidic solution would cause an electrochemical reaction during the soak. While the aluminum seems not to be reacting, I did decide to remove the screw posts from the serial and parallel ports, which were visibly accumulating bubbles and tarnishing---probably the kind of reaction I was fearing. They now have a historic looking patina on them but otherwise seem fine. There are no other signs of that sort of reaction in progress.

Having the I/O board soaking in the pan gives me an opportunity to inspect the damage caused by corrosion, at least on the component side. There, the components that seem most compromised are D6, D7, D8, Q11, and C54. D8 appears to be in the worst shape, and it is possible that the immersion has damaged it further. Some paper or plastic material wrapping the diode flaked off---if memory serves, it had the letters "AA" on it. I'd be interested to know whether it would still be safe to try using this board if any of these components are failed somehow---especially D8.

Additionally, some of the edge connector contacts where the corrosion was most evident have now taken on a dark patina, especially contacts 117 and 116 on the component side of the I/O board. I imagine that this can be made to come off if necessary.

I will continue to soak through the night and will rinse the boards with distilled water tomorrow morning. By then the soaking will have been underway for almost 17 hours.

It is interesting that the soak appears to have been most effective for the motherboard, where the metal leads rising up into the peripheral ports have changed from encrusted green to shiny metal. I wonder if the metal (zinc?) screw posts I removed may have helped this somehow---like sacrificial anodes on a ship's hull. Just a thought---I am no chemist!

--Tom

On Friday, January 24, 2014 7:07:10 PM UTC-5, Tom Stepleton wrote:
>
> I've decided that this is the weekend to address the battery corrosion on
> my I/O board, and I thought I'd ask for some advice.
>
> While it isn't causing any apparent problems (i.e. the computer still
> appears to work), it's my understanding that it's necessary to address the
> corrosion now before things get worse.
>
> I've seen a number of methods described for dealing with the corrosion,
> and one that's attractive to me is simply immersing the board in a slightly
> acidic solution (vinegar in distilled water, for example) for a while. I am
> wary of attempting to clear off corrosion via mechanical means, since I'm
> afraid of rubbing off traces or breaking leads. I am patient, so if a
> prolonged immersion is likely to neutralize the basic material that is
> causing the corrosion, I'm OK to go with that. I don't really care about
> restoring the cosmetic appearance of the board, but I *definitely* don't
> want to damage it, and I don't want the corrosion to continue.
>
> I'd love to have some advice from people who have done this before. In
> particular, my questions are:
>
> 1. Should I bother? The thing works right now---is the corrosion really
> likely to spread if I do nothing?
>
> 2. Is immersion effective, or should I try some other process?
>
> (Assuming the answer to 2 is that immersion is OK, then these questions:)
>
> 3. Are there any parts of the board that I must not immerse?
> (The paper sticker over the I/O board ROM would probably not fare well.)
>
> 4. Should I pre-rinse the boards? They're pretty dusty.
>
> 5. How dilute should the vinegar solution be?
>
> 6. How long should I immerse the boards?
>
> 7. Should I rinse the boards after immersion?
>
> 8. How long should I allow the boards to dry?
>
> 9. Are there other precautions I should take before I try to use the
> boards again?
>
> I've attached a photo that shows the rough extent of the corrosion on the
> component side of the board. Full resolution image is available on request.
>
> Thanks so much for any advice that you can offer.
>
> --Tom
>
>
>

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