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Old 06-07-2007, 02:02 AM
Grant Stockly Grant Stockly is offline
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Join Date: Jan 2005
Posts: 447
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From: Dan
Date: Sun, 03 Jun 2007 01:03:30 -0400
Subject: Re: [Altair Computer Club] 88-PPG Troubleshooting

Tarnish has been a common problem for a long time. I use see boards that
we made only a few years after the design was released(early 80's) begin
to suffer the tarnish syndrome. It's mainly due to the silver alloy used
on the old TTL/CMOS chippys which underwent severe oxidation (the
blackness of hell)--humidity is also a factor which leads to this. Some
chips that don't suffer from this contain a different alloy plating,
possibly tin. The gold isn't 24k--the purest-- probably either 14k or
16k, which can wear off from the oxidation (on the microscopic level).
The broken legs are the result when the pins are bent at the factory to
create the DIP style package. The bends contain micro fractures which
allows the oxidation to creep in, causing a chemical reaction between
the three--plating, core material,oxide. This causes the fractures to
expand even more, further weakening the tension of the leg and
eventually crack/fall off. The sockets can also be a victim from this.
I've had to replace many sockets too. One method I use --which kills 2
birds with one stone-- is to use a fine grit sandpaper(120grit) to clean
the legs. Then if any of the legs have lost their tension, they'll show
up immediately wherever it's cracked. I've had to resolder many legs
back on too.

=Dan

[ My Corner of Cyberspace http://ragooman.home.comcast.net/ ]

Grant Stockly wrote:
>
> This morning I tried to use the programmer "cold" and it failed. At least
> its not "me". The problem is for sure in the programmer or interface
> card. The symptom of only programming every other byte and not
> programming
> the bytes that it did do correctly is reflected in the logic analyzer
> reading. I have uploaded two more files. One is a picture of the problem
> and the other is a 170 second log of what happened on the programmer.
>
> 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 have 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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