Re: Corrosion abatement

Any update on the board soaking? I'm eager to see what your results are. Tom

On Sunday, January 26, 2014 1:13:16 AM UTC-5, Tom Stepleton wrote:
>
> 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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