Still no action (PDP-8/L repair)

From: Charles <charlesmorris_at_direcway.com>
Date: Thu Jan 16 07:43:42 2003

On Wed, 15 Jan 2003 22:33:17 -0600, you wrote:

>><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!

Fortunately that is not the case. All 64 X, 64 Y, sense and
inhibit lines have the correct resistance.

I found fairly quickly that B MEM ENABLE was leaving its source
but not getting to the core amps. I couldn't find the presumably
broken wire on the backplane so I ran a jumper but still no
function. (It's normally high all the time, so a disconnected TTL
input is usually 1).

this is somewhat depressing that the backplane may have reached
end-of-life, if bad wirewraps are starting to show up. It is over
thirty years old...

Now READ and WRITE are pulsing to the selectors. Unfortunately I
don't have a current probe to check out the R/W currents and
waveforms. Guess I could put a .1 ohm resistor in the line which
would give a 32 mv signal on the 320 ma pulse.

-Charles
Received on Thu Jan 16 2003 - 07:43:42 GMT