Teac FD-55GFR Issues

[tubarespect]

Hello World!

I have recently finished building an Altair 8800c. My current configuration contains a reproduction Altair CPU card, Mike's front panel interface and FDC+ controller cards, and a 2SIOJP serial card. I have successfully run Kill-The-Bit on the front panel. I have also run Altair Disk Basic, Altair DOS, and Lifeboat CP/M 2.2 from the floppy disk drives.

I am using three Teac FD-55GFR drives. All three drives successfully write to and read from their media; however, the media is not interchangeable between drives. A disk written in drive 0 cannot be read in drive 1 or 2. A disk written in drive 1 cannot be read in drives 0 or 2. And the same issue is present when attempting to exchange media written in drive 2 with drives 0 and 1. I have tested this with CP/M and Altair DOS formatted disks.

I applied grease to the transport rails on all three drives and cleaned their read/write heads. This did not make any difference. Now I am thinking that maybe the alignment is out on the drives.

For floppy disk media I am using Maxell MD2HD disks I recently unsealed.

Has anyone here struggled with the same issue I am having? If so, how did you fix it?

[AltairClone]

I’ve never had any issue with interchange between 55GFR drives, but of course, it is certainly possible. The most likely issue is index alignment (position of photo-interrupter pair that detects the index hole).

If you don’t have an alignment disk, you can pick a disk written on a particular drive and adjust the other two drives to match the index timing you measure on that disk in the drive that wrote it. Trigger your scope on the index pulse and find the point where the first non-zero data pulse occurs (2us between pulses instead of 4us between). On the drive that wrote the disk, that will be about 400us after the leading edge of the index pulse.

Mike

[Wayne Parham]

I'm thinkin' alignment too. Might be worth buying a spare drive or two while you're working through it. That way you have spares to keep your Altair running for a long, long time.

And by the way, congrats on your purchase and assembly of an Altair! Coolest micro on the planet!

[tubarespect]

I may give that a try. Thanks Mike for the info. And I also plan to get a few more spares soon. Maybe if I can find a known good spare, I can align the other drives to it.

And thanks Wayne. I had a blast building it.