PDP-11/45: MS11-L and CPU debug IV

Made some progress on the inverted result after register-to-register move problem: with the help of the KM11, extender card, and a logic probe I was able to track down that signal ALUM L coming onto the DAP is not asserted when it should be for a MOV instruction. This means the ALU is performing in arithmetic instead of logic mode and thus the incorrect result.

I next moved the extender card over to GRA, where this signal originates from a subsidiary ROM, but unfortunately at that point the MS11-L memory behavior got even worse, putting and end to these experiments. So I'll have to tackle that first...

Moved the M792 ROM over to the expansion backplane where the MS11-L resides, and it works fine there. So it doesn't seem to be a bus wiring or jumper problem onto the expansion backplane. Checked the power input pins on the backplane behind the MS11-L. 5V was a little low there; trimmed this up. Probably need to clean or replace the Molex contacts on the power distribution board in the cabinet, as it seems a few mV are being shed there needlessly compared to the output of the same regulator on the main backplane, but things seem within stated tolerances for now.

The -15V input to the MS11-L was missing entirely. Removed the DD11 expansion backplane, and added jumpers between the battery backup supply inputs and the corresponding main supply inputs, per documentation. Now have -15 to the MS11-L, but still no joy.

Will need to go deeper into the MS11-L next time...