Looking for DEC M7264-CB Troubleshooting Documentation

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu May 9 14:02:48 CDT 2019

    > From: Mister PDP

    > the 'Run' light does not come on when the switch is toggled

Yeah, it wouldn't come on full unless it somehow fell into a loop of some
kind - very unlikely. (Does that model LSI-11 have the on-board memory? I'm
too lazy to look it up! :-) And what do you have the CPU jumpered to do on
power-up? (ODT, 173000, etc.)

But I would expect to see a brief flash. (Note: I don't have an LSI-11
plugged in to check this, I'm going by memory - the -11/23 certainly does the
brief flash; if need be, I can pull out an -11/2 and plug it in, once I
figure out if they are safe in Q22 backplanes.)

I'd check the power voltages, and the clocks on the CPU board, and then look
at BSYNC, etc to see if there's any hint that the ODT ucode is trying to read
the console registers. No activity on BSYNC -> the ucode's not running.

'Small' QBUS systems - i.e. a single backplane - are OK to run with no
termination on the far end of the bus (the CPU board includes pullups for
that end), that shouldn't be an issue.


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