Re: Corrosion abatement

I'm glad everything worked out.
I didn't realize this was for a Lisa 1! Now I understand the precautions... nice work!
-Tom

On Wednesday, January 29, 2014 10:26:18 PM UTC-5, Tom Stepleton wrote:
>
> 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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