Rev "B" 4 FDC Schematic?

[Rich Camarda]

Hi All,

Anyone have a Rev B schematic for the 4FDC? I can only find Rev C, and it is obviously different. Can get to RDOS, and it selects the 5.25 floppy but get erratic stepping, and sometimes wont even select it.

Thanks in advance if you can help.

Rich

[Mike Arnold]

Rich,

Sorry don't have a schematic for 4FDC but the obvious two suggestions are: faulty drive or faulty 4FDC. If you have a 'scope look at the -STEP line and see if it is regular pulses. If the drive is not following the stepping pulses properly then it's the drive. Otherwise, it is probably bad chip leg contacts on the FDC. PITA. Take out each chip in turn, carefully clean its legs with a pencil eraser and reinsert without bending the legs. Takes ages but Cromemco left us this great pastime to fill our twilight years! 

If all else fails I could test/fix it but am in the UK (and I guess you are in the States) so another PITA. :-)

Mike

[Rich Camarda]

Hi Mike,

Thanks for advice. The drive is a known good drive, so it's the FDC. Actually many of the chips are newly replaced, but it could be bad sockets. The step line is sending pulses, but I think they are erratic or noisy. Selecting the drive also seems inconsistent. It would be much easier to trace if I had a schematic that matched the board, but oh well!

Thanks,

Rich