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Old 06-07-2007, 02:00 AM
Grant Stockly Grant Stockly is offline
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Join Date: Jan 2005
Posts: 447
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From: "Steve"
Date: Sun, 03 Jun 2007 04:17:32 -0000
Subject: Re: [Altair Computer Club] 88-PPG Troubleshooting

It's probably not the sockets. The old conductive antistatic foam
that they used to store chips on reacted badly with the pins, and
gold ones usually came out the worst, sometimes looking like they had
been eaten away by acid (isn't gold supposed to be relatively inert?
Not in this case). I have lots of chips in that condition. Silver
pins came out better, but were still susceptible. The "oxide" (or
whatever it is. Sulfide?) can be removed with a coarse eraser. I
made a little fixture that would prevent the pins from getting bent
as I scrubbed. MITS used lots of that "reactive" foam.

Usually, working the pins in and out of the socket several times will
scrape through the insulating coating. ZIF sockets are a different
matter, since they don't usually scrape the pins at all during
insertion. A trick I use with ZIFs is to partially squeeze the
chip's pins by partially closing the clamping lever. This grips the
chip, but loosely enough that I can still slide the chip left and
right in the socket a few times, causing the pins to be scraped off
for better contact. I ALWAYS do this when I blast old EPROMs, even
if they look OK.

It's tough to solder to such pins, too.

Some day, I'll buy a bottle of Tarn-X tarnish remover and give it a
try.

Steve
=============================
--- In altaircomputerclub@yahoogroups.com, Grant Stockly <grant@...>
wrote:
...
>
> A noticed that quite a few of the ICs legs are tarnished. Some are
almost
> black. This must have been from an incompatible IC and socket
combo. What
> is the best way to clean these ICs? Its possible that as things
heat up
> the legs scrape a little and get better contact? Even if the ICs
are
> cleaned, a tarnished IC must mean that the socket is bad too, right?
>
> I have a Altair 680 Ram card from Tom that has golden pin ram
chips. All
> of the chips have pins that are literally cracking off. I would
think that
> this is because of some anode/cathode thing going on. Its not the
gold,
> but the steel or what ever the legs are made of. Some crack off and some
> even break off when the chips are removed from the sockets. The other ram
> card I hvae of his has non gold plated pin 4200 chips and they are all
> fine. Same sockets.
>
> Tarnished sockets and pins is something we have to look out for in
these
> old computers...???
>
> Grant
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