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Help with Bdos Err On B: Bad Sector

D

DavidWien

Experienced Member
Joined
Apr 30, 2026
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93
Location
Vienna, Austria
This should be an easy one, but I have been away from CP/M for over 25 years. :)

I need help to analyse a Bdos Error on a Tandon TM100-1 drive, of which I have two in my Kaypro II.

Two NOS Kodak diskettes have both been formatted and Sysgened in the A drive. Placed in the A drive, either will boot the computer, and dir will display a list of files that I have copied to the disks in this computer. A>dir reports that, among other files, disk 1 has pip.com on it and disk 2 has stat.com on it. The .com files will run in the A drive.

I am now having trouble with the B drive, which has started giving Bdos errors. According to Greaseweazle it runs to speed and the stepper moves the head as expected. I cleaned the head with isopropyl alcohol, though it already looked clean.

An example of fault condition:

A>pip
*a:=b:stat.com[ov]

B drive led lights ... pause ... Bdos Err on B: Bad Sector.

I get similar messages when I attempt other operations reading or writing the B: drive. Even A>stat b: doesnt work.

Any ideas what the problem might be, please?

Thanks,

David
 
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It sounds like an alignment issue, at least what you describe are classic symptoms of that. Can you try creating a disk on drive B: and see if that succeeds (and the disk is usable on B: )? Then move that disk to A: and see if it still works. Of course, all this tells us is that A: and B: have *different* alignments, it doesn't tell which one is off. Picking the right one is required to be able to exchange diskettes with the outside world. There used to be "standard" alignment diskettes you could buy, but I suspect those are gone. If you have a drive you can prove is in alignment, you could try fully degaussed diskette and format it on that drive, then use it as an alignment disk. As I recall, the procedure was to put a 'scope on the raw read data and step around, adjusting the head for the strongest signal. First, seek track zero and adjust (include TRK00 sensor switch) for strongest signal, then step in and ensure all tracks are good - or at least track 39 is still good.

If you can't even successfully create a disk on B:, that would indication something in the drive B: electronics - maybe related to the data reception or heads.
 
Many thanks for your suggestions, Doug. The point is that this pair of drives was used a week or so ago to format and copy files to the Kodak diskettes. Since then I have done nothing to disturb the alignment that I can think of -- adjusting screws are secured with lacquer on them. I cannot now create a diskette on the B drive, but both diskettes can be read successfully on drive A. If the FDC works with one drive, why would it not work with the other?

I shall try exchanging the two drives, making A B and B A. (I hate doing this as, having large hands, I have to take the maiboard out to get at things!)

David
 
DavidWien said:
... If the FDC works with one drive, why would it not work with the other?
Click to expand...
Yes, the FDC and electronics on the Kaypro mainboard probably are working fine. But each drive has it's own heads and electronics to "condition" the analog read signal off the heads into a digital signal presented to the host (Kaypro, FDC). If the drives are getting selected properly, that doesn't leave much else. I think it's possible that a bad TRK00 sensor might also manifest this way, but probably something in the drive B: electronics.
 
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