On Sun, Jul 11, 2004 at 09:20:26PM -0400, Chandra Bajpai wrote:
> I have a couple of old 8K PET 2001s that need to be fixed.if anyone has
> some extra test equipment that they no longer need I (and the PETs)
> would really appreciate it!
I won't be at VCF-East (and I don't have any surplus test gear), but I do
have a couple of recommendations for your PETs...
If they come up to the random-character screen (no "*** COMMODORE BASIC ***"
banner) or if the RAM reads less than you expect for an 8K machine, the
first thing I'd suspect are the sockets, the next thing are the SRAMs
themselves.
Given how hard it is to find those SRAMs, it might be easier to make a
daughter card that fits into the CPU socket that has a JEDEC SRAM socket
(for a 6116, 6264, 62256...), and use A15 as a low-true enable to put it
below $8000.
The first thing, of course, would be to check the board for proper voltages
and ripple. High ripple would mostly likely be caused by dry electrolytic
caps, given that these machines are ~25 years old.
I had an 8K PET once that I sold at least 10 years ago... it was incredibly
unreliable... I ended up putting a folded cardboard wedge under the middle
of the main board to flex it "just right" so it would come up most of the
time. I don't think it was a cold solder joint - I think it just needed
new SRAM sockets.
Once you do get them working, don't forget that BASIC 1.0 ROMs have problems
with the IEEE-488 implementation. I can't recall the nature of the issue,
but they don't place nice with most GPIB gear, not even Commodore's own
stuff. BASIC 2.0 fixed that. If you are observing disk drive timeouts
or lockups, it could be related to that.
-ethan
--
Ethan Dicks, A-130-S Current South Pole Weather at 12-Jul-2004 01:50 Z
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Received on Sun Jul 11 2004 - 21:04:33 BST