Can you check that BHALT on the QBUS is actually asserted (i.e. 0V)

Don't feel bad, I too prefer to rely on an oscilloscope by default; not only does it let you see what's really happening (intermediate voltages, noise, etc) but it's simpler, and there are less ways to get incorrent info. It's not necessarily good if the 4 clocks (I take it that's what the latter refers to) are working, because if one or more of those were broken, it's a relatively easy/simple fix, whereas if they are working, and the CPU's still not running, it could be a failed CPU chip, and the only fix there is to replace it. Note that SRUN isn't crucial to the machine's operation, it's just user info. If SRUN is somehow broken on it's own (i.e. failed component somewhere between where the CPU generates it, and the display LED) finding and fixing that issue won't help. Far more useful, in terms of getting the thing running, would be to know if BSYNC on the QBUS is hopping around (as ODT tries to talk to the console - an easy thing to check into, too). If not, that's a show-stopper that needs to be looked into. The '78-'78 "microcomputer processors" says (pg. 3-15) that on the LSI-11 it's also on CH1; just to complete the complexity, it also says (pg. 3-32) that on the LSI-11/2 it's also on AH1! So maybe the CPU is actually running after all? Although turning RUN/HALT to 'HALT' should stop it - the Run light would I think go out when ODT is running. (It certainly does on the /23.) Can you check that BHALT on the QBUS is actually asserted (i.e. 0V) when the switch is in HALT? Noel