PDP-11/45: CPU debug II

Received and installed the replacement lamps for the -15V regulators. Pic below shows what the power supply looks like with all the lamps functioning.

Verified backplane DC voltages and ripple currents again, and re-trimmed all the DC regulators. Verified AC LO and DC LO deasserted and free of glitches. Found some harness wiring mistakes to the DD11 expansion backplane; corrected these.

Tried some CPU board-swaps looking for a quick win, but broken console behavior didn't change significantly with different boards.

Investigated the timing generator board, and found that the crystal oscillator wasn't oscillating. Tracked this down to inductor L1 which looked as if it had been partially sheared away from the board at some point during installation/removal/storage. Repaired this. Success! Able to load addresses from the front console now. Switches are mirrored in the BR when halted in console.

Address bit 0 seems stuck. Swapped PDR from spare board back to the original. Can now examine and modify the light/switch register, and examine the contents of the M792 ROM.

Jumpered the DD11 expansion backplane back in, and slotted in the MS11-L memory. Limited success: can modify and examine memory for example near address 001000, but cannot modify low memory addresses. In some ranges, can only modify every other word. Also, PC seems stuck at 022000.

At this point, I could really use a KM11 maintenance board set. These are pretty hard to get a hold of, but a few folks on the web have built their own reproductions. I put in a PCB order to ExpressPCB with a KM11 layout by Tom Uban (described here), and also put parts on order to stuff it.

Also, figuring I'll need to be going deeper into the CPU debug, I found and bought an HP1662A logic analyzer on eBay, for about the same money as the KM11 PCB and parts!