Hello, folks --
Yesterday I finally attempted the replacement of the Timer Chip
that is still available (presumably for other various uses,
hobbiests, etc.), which I obtained from JAMECO (www.jameco.com).
Removing the solder from the old chip was a grueling experience --
one that I'll not likely repeat. Although it was simple and
safe to practice the techniques suggested here on an old board
with the same properties as the PC/XT board, the actual task
had unique problems that couldn't be duplicated with my training
tools. Nonetheless, I accomplished the task -- and I suspect
with respectable results -- thanks to *all* the tips and tricks
suggested by those of the list.
I removed the solder with the suction tool, which worked fine
on one half of the pins (on one side); then, it no longer
functioned properly (and I was running out of time to clean it
out and replace the tip, if that's what was causing the problem).
Next, I lifted up one side of the old chip, up and down, so as
to break off the remaining legs. By suspending a clamping
tweezers on the top of each remaining leg, I removed these by
heating the underside of each allowing for the pieces to loosen
and fall. Some of the pieces were too short to remove this way,
however, and it was a difficult process to liquefy those holes,
quickly poke them through with a fine needle and later clean and
shape them with tiny clockmaker reamers and broaches (leftover
from a previous neglected hobby <g>). After carefully cleaning
up the shavings from this process, I examined the work with a
loupe to make certain nothing was damaged (it wasn't a pretty
sight under the loupe, but it was satisfactory for the desired
result).
The easiest chore was the soldering of the IC socket. The solder
flowed flawlessly around each protruding leg of the socket on the
underside of the board and clung nicely through to the opposite
sides of the socket, too. The chip slipped in snugly and
cheerfully.
After reassembly, the machine booted up smoothly and POST revealed
no errors with anything. It has run well without locking up for
at least two hours (I haven't run it longer than that yet -- am I
just a bit paranoid?), and I believe it seems rather snappier
than before.
Although these results in themselves would appear to prove that
the new chip is doing its job, the old IBM diagnostic program
*still* is not satisfied and reports the same "102" error! <sigh>
Either the problem is not solved, or that diagnostic program is
at fault.
Another possibility is that there is a conflict or malfunction
with a dual serial/parallel port card. The card itself passes
the diagnostic test, but as soon as a printer and/or external
modem is attached to one (or both) of the ports, the diagnostic
routine complains. I might suspect the modem is at fault, but
that hardly explains what could be wrong with the printer,
which works flawlessly with my other computers, old and new.
So I'm afraid that as soon as I begin using the printer or
modem on the XT, the old lock-up bug will return. Not that I
depend on this machine for these tasks, mind you -- it's just
the nagging it causes since it's an unresolved problem. And
once again, that leaves me wondering whether some previous
technician finally stored it away -- and that that's why it
was eventually forsaken and forgotten -- yet now survives as
a venerable old relic in my collection. ;-)
I'm going to let it "semiretire" with light duties. ;-)
Jerry [o:--] "The" IBM AT/5170 model 319 [--^~---] 9600kbps/30M HD
*1986 ||||||||||||||||||||||||||||||||||||| [ =====_] 512k RAM - 8MHz
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