calhoun@mcnc.org (John D. Calhoun) (11/18/88)
Summary: Strange "seek" error on a floppy disk drive
Can anyone help me fix a disk drive/controller problem? I am
planning to sell my Z100 and think I better get a problem on
it fixed first.
The model is a Z110 with dual floppies. I don't know what
brand the drives are, but their circuit boards have the MGA
(Mitsubishi) logo.
The problem is with the "B" disk drive. It is usually unusable,
apparently due to "seek" errors. This is even true after the
drive has been used to format a disk (it can't read the disk
it just formatted). When diagnostics are run on the drive, the
message is this:
1. Replace chip U30 on controller.
2. Replace the drive.
3. Replace the controller.
(so far it has not said "replace the computer.")
Step 1. has been performed with no improvement.
The STRANGE PART of the problem is that often if I run the
diagnostics repeatedly, the drive will suddenly start working,
usually until the computer is reset or until after a
shutdown/startup.
Anyone have a solution/suggestion? I have tried re-seating
the controller in its S100 slot, as well as trying it in different
slots. Also, when the problem first happened a few years ago, I
discovered a bad timer chip which I replaced. A "read" operation on
drive "B" would start and just keep trying indefinitely. It would
not abort. Well the timer part is fixed, but the seek problem is
not.
Thanks in advance.
John Calhoun
calhoun@mcnc.org.UUCP (919-859-2774 home, 919-248-1952 work)GUBBINS@RADC-TOPS20.ARPA (Gern) (11/22/88)
If the A: drive is okay, then the controller is fine and the drive is probably out of alignment. If you replaced the timming PLL or 4 phase clock chip on the controller, the timming trim pots may need to be tweeked to recalibrate the timming (B: may be more sensistive). The calibration is detailed in the Z-100 Tech Manual and requires a 'scope, frequency counter, and a voltmeter. The Heath Kit version has a calibration board that I have never seen that does it with only a voltmeter (so I am told... Info, anyone???). Gern -------