Help Fixing a C128D Drive

[fargo]

The internal drive in my 128D (plastic case) doesn’t work. `LOAD "$",8` moves the head to the middle of the disk, then returns “FILE NOT FOUND ERROR”. The green LED starts flashing after that, and the drive doesn’t respond to any command until I power cycle the computer.

When trying to format a disk using `OPEN 1,8,15,"N0:TEST,01":CLOSE 1`, the disk starts spinning but the drive’s head does not move, and I get a READY message.

I have already cleaned the driver’s head and lubricated its trails. Any suggestions would be appreciated.

Thank you!

 

[MiaM]

The 1571 (which is what a C128D has) has a track 0 sensor, so if the head is already at track 0 it won't move the heads, and it will never do a 1541 style "bump". So the head movement or lack thereof seems correct.

For testing purposes you could try inserting a disk that isn't Commodore formatted, and try formatting it, and then check if the first track is readable by another Commodore drive. If so then you know that it's able to write but not read. It's unlikely that it's able to do that, but might be worth testing. Also you might want to test some fast formatter that doesn't verify what it writes, as if it can write but not read then it should be able to format a full disk.

Also for testing purposes you could run some software that can read individual tracks/sectors, and try that on the "second side" of a disk formatted in another 1571/C128D. If that works then the problem is related to the "first side" head.

What measurement instruments, if any, do you have? If you have an oscilloscope I would recommend start with looking at the analogue read signals from the (first side) head.

 

[ClassicHasClass]

The green LED starts flashing after that, and the drive doesn’t respond to any command until I power cycle the computer.

That's an interesting failure mode. Are you able to read the error channel or does it not even do that?

These aren't obviously the same symptoms, but it sounds a little similar to an FDC failure: https://portcommodore.com/rcarlsen/cbm/1571/1571diag.txt

 

[MiaM]

Oh, I missed that it seems to lock up. That indicates a "digital" problem, I.E. bad ROM/RAM/CPU or whatnot.

Do you really have to power cycle it or is a reset good enough to get it to respond to commands again?

I don't know what test software there is for a 1571. Since it responds to commands you should be able to run test software that uploads code to the drive and runs that code and comes back with the results of the tests.