Not only did Cricklewood have them, but they arrived
Saturday morning.
That effected a partial fix.
The timing generator is a string of four bit shift registers
clocked
with 20Mhz.
Various combinations of their outputs are used to set and
reset
bistables made out of cross coupled 7440's.
As the problem I'm fixing is you can't load memory, which is
a one shot
operation, its slow old work.
A spare 8330 would confirm if that's where the problem is
and I expect
would speed up the repair on the current one.
I'll continue with fixing it and keep an eye open for a
spare. Getting
one from the US would be an option.
I also return all systems to working order. Apart from a
couple of
VT420's with ticking SMPSU's everything I have restored
runs. (Three
VAX's, Two alphas, a Rainbow 100+, DECMateII, Pro350,
Pro380, a DS3100,
a VS3100 and assorted LA printers and VT terminals)
Rod
-----Original Message-----
From: cctech-bounces classiccmp.org
[mailto:cctech-bouncesclassiccmp.org] On Behalf Of Tony Duell
Sent: 28 March 2008 22:52
To: cctalkclassiccmp.org
Subject: Re: Looking for a M8330 or a couple of SN74194's
>
> Hi Tony
> I agree that the concept of originality is important
in what we
do.
> The system I have is original in the sense that all the
parts are from
> the right era. However the current configuration is not
that as stated
> on the factory label. You could also say that any item
with a
If this is the machine I think it is, I know not only the
chap you got
it from, but also the owner before that. IIRC, it originally
had a TU56
(single drive versiun, and no I don't mean a TU55) which is
currently on
my desk, hooked up to my PDP8/e. And the RX8/e is not
original.
If you look at one of the CPU logic boards, you'll see one
of the chips
(I forget what) has been replaced. I did that over 10 years
ago to cure
a problem with the top 4 data lines in some operation or
other. The TU56
was 'payment' for that repair...
> date of later than the manufacturing date and not the
result of a
> repair or upgrade is not original.
True, and some museums, alas, take it that way, and refuse
to instal
replacement parts to keep their machines going, even if said
parts are
contemporarty with the machine. Personally, I like all my
classics to
run.
However, I also like to use as few spares as possible. If
your clock
generator was missing, or physically cracked in half, or...
then I would
agree you need an M8330 board. But if you can get your old
one to run
again, even by using more modern parts (I would have no
problems fitting
LS chips if they would work electrically, for example), then
I'd rather
keep the spare board for somebody who really did need it.
>
> Thanks for the tip re Cricklewood I will contact them.
They may only have LS or something like that. As I said, I
needed some
7495s, a rather oscure shift register chip that I couldn't
find
anywhere.
They had 74LS95, which worked fine in my HP9820. OK, not
original, but
at least I can use the machine again.
-tony
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