Power problems with C8P DF drives

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Re: Power problems with C8P DF drives

Post by dave » Fri Feb 23, 2018 12:57 am

That suggests the LM723 is bad. Try replacing it.


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Re: Power problems with C8P DF drives

Post by lowrybt1 » Fri Mar 23, 2018 1:56 am


Success repairing the PSU for the 8” drives. A new LM723 did the trick. The voltages all check out. Now a new problem, the drives do not appear to be receiving a signal from the C8. I’m saying that based on visual inspection not using a scope. The drives were working fine before the old PSU blew. Now, depressing the D key gets no response. (The C8 is running. “M” generates the appropriate memory register.) The red drive lets are off, no stepper motor action (spindle drives are spinning).

There’s one curious thing I noticed when reconnecting the PSU. Before I attached the power connectors to the drives and logic boards, the light on the white power button on the front of drive chassis was lit. After hooking up the connections, the power button light is out (but the drives are spinning and the voltages to the boards are all right.) Any thoughts about the light on/off issue.

So, out of desperation, I’m letting the drives run for a few hours on the questionable theory that some component needs to warm up or capacitor get energized. I have two spare 8” drives with logic boards but the thought of having to swap them in makes me tired.

UPDATE: When I removed the A-drive logic board, the white power light on the front of the chassis comes on. This leads me to think that there’s something wrong with the logic board of the A drive. I’m going to swap in a replacement A drive/logic board. Question: does anyone have a copy of the Siemens manual for the F-100B-8? I want to make certain I have the jumpers set correctly for the A & B drives -- as well as configuring the terminator resistor correctly.
C4PDF w. 24K, 2 x 5.25 MPI B-51 drives
C1P RevB with fully-populated 610 board and A-13. Klyball D-13.
Spares: 600 Rev.D, 610 board, 540A, A-13 with homebuilt data separator, MPI B-51 logic board (w/o data sep module) and mechanicals

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