RK05 Help

OK, some time back I wrote about a couple of RK05J drives that I have, which were connected up to a PDP 8/e, via RK8E. A few folks wrote back and said that the drive had to be connected to a controller to come up. Not so. It won't "READY" a disk, but it has enough brains locally to fire up the blower motor, light the LOAD light, unlock the drive door to allow a cartridge to be put in, and once a cart is inserted, allows it to be spun up, but the heads will never load and the drive will never go READY without the controller attached. Last time everything was powered up (over a year ago), though I was having problems with the RK8E, the drives worked fine. They powered up, blower motors ran, and you could load a cartridege, spin it up, and the drive would go ready. I could issue seeks and reads and writes...but there'd be data errors when doing so, as it appears that there's a stuck bit somewhere in the RK8E. All that aside, it's been a little over a year, and I've pulled the machine out of storage and am in the process of trying to get it back into running condition. The 8/e seems happy. I powered it up over a long period of time with a Variac, watching the main supply voltages come up, and all went well. The 2 4K core planes seem to be fine, and the 16K solid state RAM board also seems fine. I can exam/deposit stuff, toggle in small programs (light chasers, etc.), and they work fine, and reliably over time. The problem is the RK05's. I've disconnected them from the RK8E, have installed the terminator card in one drive. I power it up, and the blower motor doesn't start. But, the POWER and LOAD lights light up on the front panel, and the drive door unlocks with a clunk. I've checked all the power supply voltages (+15, -15, +5) under load, and they all are within spec, with minimal ripple. The "CONTROL & INTERLOCK" board in the electronics package in the drive has the circuitry that controls the blower motor. There is a "safety" relay which gets pulled in when all of the DC power supplies are good, which is done by some circuitry on this board. The result is a "DC OK" signal, which is active when the drive is powered up. A derivative of this signal drives a driver that energizes the "Safety Relay", which has multiple contacts. One set of contacts applies power to the blower motor, and others do things like dump the charge in the NiCd battery pack into the head windings to do the emergency head retract when power dies. I've traced the circuitry from the DC OK signal generated on the CONTROL & INTERLOCK board, all the way through the harnesses and to the relay, and from the relay to the motor, and all are healthy. The safety relay does pull in as expected when he unit is powered up. However, the blower motor will not run. I've checked the relay contacts...they are fine. 120VAC is present on two of the three wires that go into the blower motor. There is a 5uf motor start capacitor that, from what I can tell, seems fine. But...the motor doesn't spin. The funny part is that both RK05's act this way. I'm puzzled. The motors aren't seized -- they spin very freely. I've put an ohmmeter across the windings of the motor and there are no shorts or opens. I'm really stumped! Could the start capacitor be bad? I don't know much about how these types of AC motors work. I swapped the start capacitor with one from another "parts hulk" drive that I have, and it didn't make any difference. Any ideas, anyone? Rick Bensene The Old Calculator Web Museum http://oldcalculatormuseum.com