Re: CBM Drive Mechanisms

From: Nicolas Welte (
Date: 1999-08-11 22:57:07

William Levak wrote:
> The stepper motor is connected to the Commodore system board through this
> circuit board.

No, Bill, it's the spindle motor. The stepper motor is always connected
directly to the drive's main board.

> Nicholas reports that on his 1541C drive there is a track 0 sensor that
> gets it's power from the Commodore system board, but connects the output
> signal to the stepper motor board.

I didn't say this. I said that the WP LED is connected to the spindle
motor control PCB, and it was on the Chinon drive.

> This makes sense because none of the 1541 ROMs and none of the Commodore
> system boards provide support for a track 0 signal.

250448 has an input for the track 0 sensor, it's mostly disabled by a
short to GND (It was via J3, I think), but otherwise connected to PA0 of
the bus VIA. The ROMs 251968-01 and 251968-02 have support for this
signal. The 1541-II has the GND connection to PA0 left to enable this
board to work with the two above mentioned ROMs. But the drive was only
shipped with 251968-03 which had the sensor support removed.

> If the track 0 signal
> is connected to the stepper motor board, then it can turn off the stepper
> motor at track zero without any active support from the Commodore System.

I'd really love to see this solution in any Commodore drive. But I never
did. BTW, my SFD1001 also has a track 0 sensor, but doesn't make use of
it. Neither in hardware or software.

> It appears then that the same Newtronics D500 drive mechanism is used on
> all 1541 drives, only with different connectors and the track 0 sensor
> removed on some.

I agree with you here, but the sensor probably doesn't have to be
removed. Like on my 250442 board, where there's simply nothing useful
connected to the track 0 sensor pins.

> This would also mean that the drive mechanisms should be compatible
> across all the 1541s if you change the connector.

This is true.


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