PDP-8/L repair - test-drb@ccmp.vtda.org

15 Jan 2003

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 From: Charles &lt;charlesmorris(a)direcway.com&gt;

On Wed, 15 Jan 2003 12:00:01 -0600, you wrote:

 If you have an extender card, you should
be able to trace the fault pretty quickly with a logic probe or
an oscilloscope.

Without an extender card, it's a lot harder. 
I agree. I have both an extender card and a scope, fortunately,
and have been using them extensively!

   This
weekend, after quite a bit of signal chasing, I found that I
 had put the variable delay line in the wrong slot some time ago
 while cleaning connectors/mice nests! 
I've done stuff like that. 
The problem was, since my machine does not come with the parity
option installed, there are a few empty slots in the otherwise
unbroken string of handles touching each other...I still am
annoyed for doing it to myself though ;)

Now to fix the core memory.
<HOPE> Shouldn't be too hard to find </HOPE>
since it's doing nothing. If it had flaky bits or words or pages,
different story, but absolutely dead can only be a few things. 
Ya, like a broken core sense wire!

 For the times I don't have an extension card, I solder some
wires to points I expect to measure and tape them to a strip
of wood that I lay on top of the machine. It is slow but
works OK. It wouldn't work on a real fast machine because
of reflections of unterminated lines but these older machines
are not all that troublesome with one foot or so of wire.
Dwight

...

-Charles