Help with a busted MSV11-L?

Noel Chiappa jnc at
Sun Dec 7 11:25:35 CST 2014

    > From: Jon Elson

    > Power the system off for 10 minutes, then power on and read various
    > locations. If data bit 4 shows 1's and 0's, then the reading is OK, and
    > it is the writing path that is stuck.

I'm not sure this will work, as the anomalous voltage I see (2V) is after the
output (i.e. to the QBUS) data latches, but before the bus transceiver: i.e.
in the output (reading) path. So I know it's the output data path that has a
problem, not the input.

The only question is which of three chips on the output data path might be
the cause of the problem; one of the two three-state latches (one for memory
data, one for CSR data), or the bus transceiver. As far as I can tell, those
are the only three devices attached to that conductor (where I see the
constant 2V).


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