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

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

The major issue is mechanical: 8050/8250 drives are 100 TPI and 'PC style' drives are either 48 TPI or 96 TPI; you might be able to get one to work but it wouldn't be compatible with any other 8x50 drive.

Tandon and Micropolis (and probably MPI as well) did make 100 TPI drives for other computers, but they're pretty rare; if you found a 48 or 96TPI drive from the same manufacturer (Tandon, Micropolis or MPI) you might be able to replace the stepper assembly, but I doubt that it would be worth while.

m

----- Original Message ----- 
From: "Mia Magnusson" <mia@plea.se>
To: <cbm-hackers@musoftware.de>
Sent: Monday, March 19, 2018 6:58 PM
Subject: 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.
> 
> -- 
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