OK, right.... I seem to rememebr that the older version of 11/05 CPU board used an RC oscilaltor for the UART clock (rahter than a crystal). That may have drifted. You can check th efrequency at the TxClk and RxClk pins of the 40 pin UART chip on one of the CPU boards, it should be 1760Hz (16* the baud rate, I assuem your Mdoel 33 is 110 baud). I think you can do a simple test without a program. Read the Receive CSR CSR, I think), and check the ready bit is clear (if not, read the receive data register). Then pres a key on the teletype and see if the ready bit is set (re-read th CSR, of course). Then read the data register and look at the bit pattern (low byte), it should correspond to the character you typed. Yes, you do.If you don't ahve the reader PSU connectoed, I think the reader trip coil will still work, the transmit clutch will engage and the distributor will spin, but the reader itself will do nothing. I've not looked at your pictures, do you have a free cable coming out of the Model 33 ending i na 15 pin socket to connect to the reader PSU? As I suggsted in my previous message, there are really 2 circuits, for the tip coil and for the reader solenoid, You cna debug them in either orrder, but of course you need to have both working in the end. If it _is_ a transfofmer, I am totally puzzled as to what it could be doing there. I asusme this is the voltage betwene the pins. The voltage from the pisn to eather is irrelevant, of course. It's been a long time since I looekd that the 11/05 printset (I can dig it out if need be), but it's quite possible that one ed of the relay coil goes to -15V nd the other end to +5V 9and thus there's 20V across the xcoil) with a switchign transistor in series with onoe of the wires so the PDP11 can cotnrol the relay. Thinkin about it, the relay may well not actuate until a bit in the receive CSR is set (this the reader is normally stopped, it single-steps when the PDP11 wants ot load something). I think I'd use a bench PSU or a couple of 9V batteries in series for testing. The simpler something is (battert as agianst a PDP11 PSU and control ogic), the fewer unknowns there are :-) Well, the polarity clearly depends on which way round you conenc the voltmeer... I think that reader control oop can provide enough current to operate small relauys without damage. The voltage is high enough too. -tony