3743Altair Floppy Drive Troubleshooting/Repair
- Apr 17, 2014Hello, folks,
I have an two original Altair 8" floppy drives for my Altair 8800
The system as an original MITS floppy controller.
One drive works perfectly.
The other one, though, has problems. Every read attempt results in I/O
The drive is a Pertec FD-400.
I've cleaned the head carefully. I have checked all of the connectors
and cables and all is well there.
The drive select logic on the buffer board is working properly.
The spindle drive spins the floppy just fine, and the stepper motor
moves the head in and out smoothly. The head load solenoid properly
loads the head and pressure pad when commanded.
The Track 0 switch is working as it should. The index sensor is working
I can look at WRITE DATA going into the drive when the system is doing a
DSKINI (using Disk Extended BASIC), and the data is going out to the
drive just fine is clearly visible on the oscilloscope. I have taken a
disk that has been initialized on this drive with DSKINI, and I can see
that it has been initialized -- there are no files on the disk, and I
can put files on the disk and read them back just fine. So, it appears
that the write circuitry is working fine.
However, when I issue read requests to the drive, the READ DATA does not
appear to be coming out of the drive. I have checked all of the
circuitry in the buffer board to make sure that there wasn't a problem
there, and all seems good.
It appears that there's something actually wrong in the read circuitry
in the drive itself.
I've downloaded the Pertec FD-400 drive manual from bitsavers (I can't
thank Al Kossow enough for this amazing resource), and the read
circuitry looks pretty simple, just three IC's and a few diodes and
transistors, so I guess the next step is to start probing the drive
itself to see if there's a problem there.
I haven't scoped anything in the drive yet. I was hoping to avoid that.
I just hope that the problem isn't with the head itself, as that'll be
almost impossible to find a replacement for.
Just out of curiosity, and to perhaps save some of my time in exchange
for paying someone to fix the drive, I sent a query to M. Farris &
Assoc. to see if they could fix the drive. They wrote back and said
that they no longer support the Pertec FD-400.
I'd really like to get two drives running on the system, as it makes
things a lot easier for disk backups and provides more usable space.
Does anyone have any ideas short of digging into the drive circuitry?
Does anyone know of a place that will still repair these old FD-400
Thanks for any advice,
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