8050/8250 schematics - replacing the drives and analogue board with PC style drives

Hi!

Are there any better schematics of the 8050/8250 drives available
somewhere?

I've checked out all stuff in this dir:

ftp://www.zimmers.net/pub/cbm/schematics/drives/old/8050/index.html

The schematics of the various analogue boards are good, but the scans
of the digital board are so bad that it's hard to tell what some
signals do.

In this thread someone has an 8050 with mechanical problems:

https://www.facebook.com/groups/214556078753960/permalink/812150445661184/

This made me think that it might be possible to use standard PC style
drives.

By looking at the schematics for the various analogue boards I've
determined this:

Spindle motors are controlled the same way as a PC style drive, a motor
on/off signal. Not sure if the logic levels are the same.

There are two select signals which select which drive mechanism that
should be read from or written to. There is a side select signal for
the double sided drives. Read data is always driven by the analogue
board. It should be easy to use PC style drives with theese signals,
but mixing a PC style drive with an existing analogue board would
require an enable/disable function for data output.

The problem is the head position stepper motor signals. From the
digital board there are two 2-bit counter signals to the analogue
board, one for each mechanism. Those are decoded by 2-to-4 decoders and
results in driving one of the four coils in each stepper motor.

One problem here is that they are enabled by the motor signal, not the
drive select signal. So to be able to use PC style drives it would
probably be necessary to hold the drive select lines constantly active
(low) for the PC style drives, gate the read data outputs and write
enable inputs with separate logic, latch the digital boards stepper
motor "counter" outputs with the motor signal.

The other problem is that the signals aren't compatible. Each change of
the two bit signal must be detected and converted to a STEP pulse with
the right polarity selected for DIRECTION.

But this is assuming that the digital board can do anything. By looking
at the schematics it seems like the digital board itself has some kind
of logic in the interface to the analogue board, but the quality of the
scans are too low to be able to tell what it does. If it were possible
to read, it might reveal something that could simplify the circuit
needed to adapt PC style drives.

-- 
(\_/) Copy the bunny to your mails to help
(O.o) him achieve world domination.
(> <) Come join the dark side.
/_|_\ We have cookies.