Needs help w/ diagnosing and hopefully repairing of a DEC Tape Drive

This looks very like a Cipher drive to me. Rather later than the F880 I've had in bits on my bench recently, but some parts look very similar.... The technical manual implies these are simple DC motors (the F880 ones certainly are). It appears there are 2 connectors. One going to a cable going into the side of the motor (is this just 2 wires?) and one going to something on the bottom. Since unlike the F880 the arm against the takeup hub is not a tachometer I am guessing there is tacho on the bottom of each motor and that's what the second cable connects to. The F880 motors just have 2 wires. When I had mine in bits I tested the motors by connecting a bench supply to said wires. Those were designed to run at 30V or so. No ideas what your ones run at, but if I am right about 2 wires going into the motor itself you could try applying DC between then (disconnected from the rest of the unit, of course), turning up the voltage and seeing if the motor will run. My guess is that it will. A DC motor rarely goes intermittant in the way yours has. It may fail totally, it may need to be flicked by hand to get it going, but it is unlikely to sometimes only make a partial turn. My next guess is that he problem is the tachometer on the bottom of the motor. That, I assume, is how the control circuitry detects if the motor is turning in the self-test. If it doesn't get what it likes, then it will give the error. I don't know how easy it is to take that apart (as my F880 doesn't have it) but it might be worth invetigating. I set up the F880 tacho arm from scratch so it can't be that hard!. It may be a good idea to remove the motor first. On the F880 you need a special tool to set the hub height if you take said hub off. I had to make said tool (assuming my drive was initially rght). It looks as though you can set up this unit without anything like that, but it is still worth measuring the height of the hub (in some way) so you can get it back in the same position. Have you tried service aid 111? That should let you run the motors. It appears that error 50 is not a generic motor error, it is given as 'No Tachometer phasing'. Since it suggests replacing the supply motor, I think that my guess that the tacho on said motor is at fault is not a bad one :-). Of course it could be a problem with the electronics it connects to, or the wiring, but you have to start somewhere. The sensors in the F880 are quite simple and it didn't take me long to work out what to ecpect from them, the one on this motor may be understandable too. How many wires does it have? If it's 3 then I would expect power, ground and signal. If 4, then I would expect 2 signals in quadrature to give speed and direction. I don;t know how easy it is to take the motor apart (I did the ones in the F880, but they do not have tachos on the bottom) but it's got to be worth a try! -tony