Re: Corrosion abatement

bcc: James MacPhail

Hi Tom,

Still waiting. By yesterday the boards (esp. the motherboard) still smelled a bit like vinegar, and some dark tarnish had appeared on some of the contacts on the edge connectors*, although probing with an ohmmeter revealed no apparent change in their conductivity.

I concluded that I may not have sufficiently rinsed the boards after the original soak, and that slow reactions from acidic residues from the soak might still pose a threat to the boards in the future. So last night I rinsed each board for several minutes under the sink faucet, then soaked them for a while in distilled water to (hopefully) disperse any solutes from the city water. After that, a painstaking drying process involving spray dusters and blotting with paper towels. The boards have been air drying since midnight last night. I am inclined to allow them to continue drying until tomorrow.

As mentioned in the previous email, it would be a real comfort if an expert on Lisa electronics had some idea whether it would be safe to try powering up the boards again if I/O board diode D8 (which looks like it's in bad shape) is no longer diode-ing. Being fairly uneducated w.r.t. electronics, I am wary of probing D8 with my multimeter in case the act of probing would also affect other parts of the circuit. However, I'd be willing to try it if it carries no risk of harm.

As a final note (not counting footnotes), the COP421 chip, which had also been soaked (out of its socket) due to some slight corrosion on one pin, had accumulated a dull coating on its legs after the soak was complete. I was able to scrape this off with my multimeter probe tip, and the legs are shiny again.

So: stay tuned tomorrow for the results.

• This tarnish had actually started appearing partway through the soak, although it seems to have worsened slighly and stopped afterwards. Curiously, the tarnish seems to be entirely absent on unused contacts, and present in various proportions on other contacts. I hypothesize that the tarnish is strongest on contacts that have carried more current per unit area, with power supplying pins the most strongly tarnished, although I haven't checked schematics or followed traces to verify this correlation.
• continued: Since I assume the contacts are some sort of gold alloy, I researched online instructions for cleaning tarnished gold. These tended to suggest soaking the gold in soapy water for a few minutes and then wiping with a cloth. Since the tarnished contacts still appear to conduct well enough, I opted not to try this full procedure and instead did a little bit of scrubbing with a soapy paper towel. This appeared to have a slight cleaning effect. I didn't try too hard on some of the I/O board pins, where corrosion from the battery gave some of the contacts a slightly wrinkled appearance---I was afraid that the contacts were not very well bonded to the circuit board any longer.

--Tom

On Tue, Jan 28, 2014 at 11:57 AM, Tom Frikker <tom.frikker_at_email.domain.hidden> wrote:

> 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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