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Started by Rabs, 18:20, 29 May 22
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Quote from: Rabs55 on 19:44, 29 May 22Great thanks, I will have a look at the circuit diagram from the service manual and trace the logic gates and cable.What about the tape? Red herring or unrelated?
Quote from: Bryce on 19:22, 29 May 22A bad command could mean that the OS ROM is not initialised ie: the 40015 has failed. However, if the drive starts spinning after entering a command it means that the ROM reacted but the drive didn't. This means that one of the buffer IC's to the drive (74LS32) has failed / didn't pass the command from the 765 (disk controller) to the drive or the flat cable to the drive has a problem. You'll need to test the outputs of the buffers IC's first. If these are good, the the cable has a problem.Bryce.
Quote from: Bryce on 08:15, 31 May 22Sounds like you found a possible culprit.Bryce.
Quote from: Bryce on 18:42, 31 May 22The tape issue is most likely dirt on the head, a mis-aligned head or the tape turning too slow or not uniformly. Tape loading issues are usually mechanical problems, not the electronics.Bryce.
Quote from: Bryce on 19:35, 01 June 22I assume then, that it was only floating because the drive wasn't attached? If a drive is attached it shouldn't be floating.Bryce.
Quote from: Rabs55 on 21:07, 02 June 22Sort of. I was wondering why the CPC needed a side 1 select signal. Well I guess it does not. The "not used" written on the schematic gave the game away a little.
Quote from: Rabs55 on 18:01, 17 June 22Loaded FutureOS and run the System Monitor, on the advice of @GUNHED, and &FB7E is returning &FF. On my working CPC it returns &80.
Quote from: GUNHED on 19:36, 17 June 22Quote from: Rabs55 on 18:01, 17 June 22Loaded FutureOS and run the System Monitor, on the advice of @GUNHED, and &FB7E is returning &FF. On my working CPC it returns &80.When the value &FF is read, then the FDC can for some reason not be accessed. Now it can be a problem with a small chip or the FDC itself. But the hardware guys will know better.
Quote from: Bryce on 13:03, 15 July 22The op-amps are not in any way involved with the power supply circuitry (other than requiring power themselves).I'd start going through the FDC pins and monitor what each one does when you do a CAT.Bryce.
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