Repairing A4000 leaky NiCd damage?
tothwolf at concentric.net
Fri Jan 2 19:08:35 CST 2015
On Fri, 2 Jan 2015, Peter Coghlan wrote:
>> Went through this entire process on my A4000 a couple of years back. In
>> my case there was damage to traces underneath several of the adjacent
>> chips and the clock chip was dead to boot. I would suggest soaking the
>> board overnight in dilute vinegar in addition to washing, since the
>> alkaline crud gets into via holes where washing won't dislodge it. If
>> traces are not already eaten, this may eliminate the need to remove the
>> DIMM sockets.
> I've often seen it suggested that acid or alkali contamination should be
> neutralised somehow. In theory it seems like the thing to do but I've
> always had doubts about how successfully this can be done and whether
> the cure might do further damage on top of the original contamination.
> In practice, I can't see how it would be possible to get the
> concentration of neutralising agent even approximately right and how it
> would be possible to cover all the contaminated areas and yet avoid
> getting it on non-contaminated areas and maybe causing new damage there.
> And then there's the wondering whether the resulting wet salts will do
> different or worse damage than the original contamination before they
> are washed off and whether they might be dangerous to people?
> Unusally for this list, everyone seems to agree that it is the way to go
> but it still seems a bit black art to me. Yet we have long and
> inconclusive debates about retrobrite and the like where there are
> opionions on both sides of the fence. I'm not saying I'd like to have a
> big debate about this, just wondering if I'm missing something
I recently re-re-summarized the process over on the EEVBlog forums after
Dave Jones found his Apple Lisa badly damaged by the on-board batteries.
(I don't know if he will repair it, but I think it would make for a good
how-to video for this process should he decide to do it.)
I'm not sure how many times I've mentioned the process I use in
neutralizing the alkaline mess from leaking NiCd or alkaline batteries
(finding those old messages isn't easy with the archives down), but I know
lots of people have used this technique successfully.
"Basically, you clean the entire affected area (multiple boards in the
case of this Lisa) with white vinegar and scrub at it lightly with a
toothbrush (even get down into the card edge sockets, although they will
likely need to be replaced later). The NiCd material that leaks from the
batteries is highly alkaline, so the vinegar, being a mild acid, will
neutralize it. You then need to rinse the boards with lots of water in a
sink to make sure you flush out all the vinegar because any remaining
vinegar would also be mildly corrosive. Flushing with vinegar and
scrubbing away any buildup will stabilize the boards and stop further
corrosion. Simply cleaning with isopropyl won't neutralize the battery
mess and even if you clean off a lot of it, without neutralizing, the
boards will corrode up again."
"The next step, if you wanted to go a little further with cleaning, would
be to lightly scrub the corroded areas using a baking soda and water paste
with a toothbrush, followed by another water rinse. This will remove the
bulk of the surface corrosion on any exposed copper traces, component
leads, etc. and also helps neutralize any remaining vinegar."
"The cleaning/stabilization technique is very simple, but a little messy,
so you'll want to clean the boards in a sink. Some people claim you need
deionized water for this sort of thing, but I've been using tap water to
do this for decades and have yet to have any issues with it."
"As for the discoloration and tarnish under the solder mask, once the
board is neutralized with white vinegar, it shouldn't corrode further.
Unless there is already a break in a trace, those discolored spots are
best left alone."
"I've repaired 100s of battery damaged boards and very rarely did I need
to scrape away the solder mask. The discolored spots are just
tarnish/oxidization of the surface of the copper trace just under the
solder mask. Tarnish under the solder mask is really more of just a
cosmetic blemish and will not affect the conductivity of the copper trace
itself. What seems to happen is that there are microscopic holes or weak
spots in the solder mask and when the batteries leak/vent, it tarnishes
the surface of the copper."
"Unless the solder mask is actually bubbling up and peeling or flaking off
the copper, messing with it will cause more harm than good. If the solder
mask is peeling, then that probably means the solder mask wasn't applied
well and battery electrolyte actually got in between the copper and solder
mask. In that case, the baking soda paste and toothbrush technique I
mentioned is likely to remove any loose solder mask anyway, so you
probably wouldn't have to scrape it."
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