Re: Corrosion abatement

Results:

I reassembled the Lisa's card cage this evening, and to my great satisfaction everything appears to work: power-on tests pass, the Office System boots, the Twiggys work, mouse and keyboard are OK (so presumably the COP421 wasn't harmed), and the parallel port card is recognized. I haven't tried the serial ports---that will have to come later.

The voltage across D8 is measured at 6.18V, so it seems like it's doing fine for now.

>From here it will be necessary to monitor the condition of the boards over
time, to determine whether corrosion from the original alkaline material is abated, whether residues from the acidic vinegar bath are still present and active on the board, or whether components with corrosion damage are still susceptible to other forms of degradation (e.g. good old fashioned rust on the leads).

Regarding earlier posts on this thread---the idea of soaking in a mild acidic solution is sensible when you consider that the original corrosive substance that leaked from the battery is already alkaline, not acidic. The concern is that this substance, a solid, may not be particularly soluble, and also has had years to infiltrate leads, traces, and other surfaces---potentially making it hard to remove even with a detergent or other solvents (e.g. alcohol). Instead, the intention of the acidic bath is to penetrate these infiltrations and neutralize the base where it sits, yielding a salt. This salt poses less corrosive risk, at least in environments with normal humidity. While the neutralization is occurring, the diluted vinegar is a fairly mild acid with roughly the pH of Coca Cola---the expectation is that it's unlikely to cause much damage to the circuit board or other components, as long as the soak does not last more than a day or so, and as long as the solution is thoroughly rinsed afterwards.

(Note regarding some specific comments: acids are not uniquely corrosive, and it is certainly not the case that alkaline substances are somehow "safe". I would advise against pouring drain unclogger (e.g. Drano, Rorax), which contains some strongly alkaline chemicals, on your I/O board. Mild alkaline solutions such as are obtained with common household soaps are not so harmful of course, but those do not neutralize alkaline substances already present on the board.)

My advice to people attempting this procedure is as follows.

First, stay tuned for updates---I am OK on day 1, but there may be further side-effects to report down the road.

Second, if you wish to soak the motherboard, remove the screw posts for the parallel and serial ports, as well as the angular brackets to which they attach---these appear to tarnish rather rapidly in the acidic solution.

Third, do not use aluminum roasting pans---instead, use pans made of some non-metallic material (e.g. glass, plastic) provided that material doesn't have too strong a tendency to build a static charge. In retrospect this may have been obvious, but I was nervous about ESD and liked the idea of a conductive pan.

Fourth, a soak for longer than 12 hours is probably overdoing it, and even that is probably generous. However, the "right" amount of time isn't really apparent right now---it would probably require some experimentation to determine what that is, and it would probably also depend on the amount of corrosion present on the board.

Fifth, a kitchen is a fine place to work on electronics. You can do the teapot steam trick that James MacPhail mentioned upthread, you can rinse to your heart's content under the faucet, and you can lay down aluminum foil as a work surface and even hook it up to your house/building's ground by draping it into the sink :-)
A cooperative spouse/partner/roommate etc. helps considerably.

--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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