clh333
Veteran Member
When I power up the unit the screen displays a seek error message in three languages which is the result of a jump in the BIOS code based on an error number (9) returned to the startup routine. From what I read in the Western Digital 1773 data sheet (p. 1-7) this error is returned to the CPU by the FDC during a RESTORE command, presumably at startup. If after 255 step commands are issued to the drive without Track0 going low the FDC ceases operation and issues an interrupt. In operation the drive 0 light flashes briefly, both spindles turn for about three seconds but neither head moves.
This unit, which would not boot when acquired, has been disassembled, cleaned and the PSU AC capacitors replaced. The two Tandon TM-50-1 drives have been examined, cleaned and tested independent of the unit and found to be operational, i.e. motor light comes on, spindle rotation starts and stops as expected, rotation speed within 1% of 300 RPM, head steps to track 39 or 41 and stops at track 0. Both drives have the same configuration with the Tandy cable-select system used to differentiate them. A 180 Ohm resistor array terminates the last drive.
I would like to ask for advice on how to track down the source of the problem. I could start replacing ICs until something happens but it would be nice to have an idea of where to start. Thank you for your suggestions.
-CH-
This unit, which would not boot when acquired, has been disassembled, cleaned and the PSU AC capacitors replaced. The two Tandon TM-50-1 drives have been examined, cleaned and tested independent of the unit and found to be operational, i.e. motor light comes on, spindle rotation starts and stops as expected, rotation speed within 1% of 300 RPM, head steps to track 39 or 41 and stops at track 0. Both drives have the same configuration with the Tandy cable-select system used to differentiate them. A 180 Ohm resistor array terminates the last drive.
I would like to ask for advice on how to track down the source of the problem. I could start replacing ICs until something happens but it would be nice to have an idea of where to start. Thank you for your suggestions.
-CH-