
Barn Find MOS MCS6502 – A Restoration - sohkamyung
http://www.cpushack.com/2020/01/14/barn-find-mos-mcs6502-a-restoration/
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cbmuser
I cringed when he removed the CPU with a screwdriver from the board after
spraying it with WD-40.

First stating how rare these white 6502s are, then use brute-force methods to
remove the chips off the board.

He could have at least used a proper chip-puller. Seeing those bent pins on
40+-year-old ROMs breaks my heart :(.

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philpem
There's nothing wrong with using a screwdriver to remove a chip like this,
provided it's done carefully. With that said, I'd probably have used a guitar
pick.

Some of the chip pullers are excessively violent and apply force to both ends
of the chip. If the centre pins of the chip are stuck, the chip may end up
being snapped in two.

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yardie
So I was given a binder of 6502s and a bunch of EEPROMS as a kid. I’m pretty
sure they are still sitting in that black foam in a barn. So how does the foam
rot the pins?

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h2odragon
Collects moisture and keeps it right there by the pin. There might well be
some chemical breakdown too, the older foam loses its spring so must be
changing composition as it ages.

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bullen
Ok, so having chips in foam indoors is safe? I have a SID in foam, don't know
how else I would store it?

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philpem
The more modern foam isn't quite as bad, but keep an eye on it. Clean the pins
and replace the foam every now and again.

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ggm
Is there any good evidence of vlsi ageing? What chemical or electro chemical
reaction would be causative?

Capacitor ageing is pcb dielectric leakage. Coils rust. Chips? Sealed, layered
devices?

Thermal stress, I could believe

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anticodon
I've heard that diffusion can disrupt work of diodes and transistors by
corrupting p-n junctions. Don't know what time is required for diffusion to
destroy p-n junction and couldn't find an answer via Google.

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_ph_
Yes, that is a major factor in aging of chips. But giving a number for this is
very difficult, as it varies on a lot of parameters. Quite a lot depends on
the process the chip was manufactured with. Older processes with larger
feature sizes usually are less affected than modern processes with smaller
structures. But almost all details of processes are confidential and available
under NDA only, so not openly published. Also, it depends on the concrete
designs. That is, why the carrier migration is simulated as part of the modern
design process. Of course, also the operation conditions play a role. The
hotter the chip is and the higher the operation voltage, the quicker the
diffusion happens.

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zentiggr
Had a single board Synertek kit, 6502 based with 2112 RAMs... in 1979? Had to
do the math, didn't realize it was that "late" in the 6502 history.

Such a fun fun processor to work on at age 12... and I've always been grateful
to have learned programming from the ground up. Always feel closer to the
metal since I am aware how many layers there are under whatever I'm working
in.

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LIV2
Cringed at the wooden block, older ICs like that are a lot more sensitive to
ESD damage than modern ones, he should have covered that end of the wooden
block with foil.

Cool that someone has found a working 6502 from the first batches though! I
wonder how many are left out there...

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Kirby64
You sure about that? Maybe 6502's are old enough before proper ESD protection
circuitry became mainstream, but generally smaller nodes are a lot more
sensitive to ESD damage than the ancient stuff since the size of features back
then just was so much bigger.

There's a reason why HBM ESD limits have gone down over time... just because
it's physically impossible to protect against a certain level of ESD when
you're running ultra high speed circuits.

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LIV2
That's a good point, I think I'd just heard that a long time ago and not
really thought about it but with much larger features it should actually be
more resilient.

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philpem
The original 6502 was also built on an NMOS process, not CMOS. It's CMOS which
tends to be more static-sensitive, especially early CMOS.

I'm not sure where CBM/MOS's HMOS process (used for -- IIRC -- the SID and
VIC) fits in.

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Zenst
Breadboard on a PCB [http://www.cpushack.com/wp-
content/uploads/2020/01/BarnFind_...](http://www.cpushack.com/wp-
content/uploads/2020/01/BarnFind_3.jpg)

You often see correction wires on early PCBs but a breadboard - that's some
hacking in my definition right there.

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andoma
Related:
[https://www.youtube.com/watch?v=wVphFkaX1gg](https://www.youtube.com/watch?v=wVphFkaX1gg)
(Restoration of a C64 left outdoors for over a decade)

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fnord77
how does "black foam" rot the pins off chips?

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tyingq
I'd read a discussion some time ago that guessed it was the adipic acid
present in some types of polyurethane foam. Polyethylene foam doesn't seem to
have the issue.

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bullen
Ok, but how can you tell the two apart?

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tyingq
Springy/spongy/wet/heavy feeling vs mostly stiff/dry/light.

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bullen
Ok, so stiff/dry/light is polyethylene = good?

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tyingq
Yes.

