OK, the first obvious thing to check is that the logic power supply is there. It's -15V, the chassis can be taken as 0V. This is unlikely to be the problem, but you don't want to spend time working out why nothing works, only to find it's got no power. The register label is lit by a couple of T1+3/4 bi-pin bulbs running directly off the -15V supply. They might be burnt out. The error lamp is a similar bulb running from a transistor driver on the left sideboard, this bulb may also be burnt out. With a machine as complex as the 9100, it is well worth making sure trivial things are right before diving into the logic. The lack of processor information in the manual is one reason I traced out the schematics :-) To be fair, the service manual is useful for the PSU and display sections. But if that's not the problem, you need the schematics. Have you read the interfacing manual? Read with a hackish eye it gives away a few of the 'secrets'. One trap for the unwary, the flip-flops are current-operated (the J and K inputs are to the bases of transistors with the emitters held at -1.4V). So you won't see much there with a 'scope. The outputs of the flip-flops (E and F) do swing by almost 15V, and are easy to measure. This might be bad connections. It's worth removing the keyboard, card reader and processor chassis, then taking off the sideboards (3 screws each) and making sure they connect correctly to the gating board and the ROM assembly. Note that the machine will work without the card reader. It will not work if the keyboard is not plugged into the processor. Well, you don't know the error lamp is good :-). Worth checking. The processor will run and give errors with a faulty CRT (or CRT driver circuits, EHT power supply, etc). But if the CRT is internally shorted which can happen if the electrode supports break in shipping, you can and up with a couple of hundred volts on the processor. This wipes out diodes and transistors... -tony