Re: CBM Drive Mechanisms

From: Nicolas Welte (
Date: 1999-08-12 13:21:20

William Levak wrote:
> > 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.
> OK, but this causes further problems.

Why? Pins 1 and 2 are just the power supply of the WP LED, what problems
arise if the power is supplied through the spindle motor PCB?

> It's 250442 and 250446 (1541A) that have the input and it is jumpered out
> by J3 and it was shipped with the drive without the sensor.

Aha, I had a look at the schematic for those drives and you probably
mean the input at pin 14 of CN6 or P6. You're right, this input is
somewhat connected to an optional circuit, but this is not related to a
track 0 sensor. As I understand that circuit, it will activate the
spindle motor for some seconds each time it is triggered by a disk
change signal. This disk change signal can either be generated by the
write protect sensor (J3 closed) or by an extra disk change sensor at
pin 14 of CN6 (J4 closed), but I've never seen a drive with that extra
sensor or the optional circuit.

The functionality of this circuit has been delivered by software in the
later 1541C drives, if they were equipped with the 1541B board and the
proper firmware. 

> 250448 (1541B) has the power for the track 0 sensor, but where does the
> output signal go??

Pin 6 of connector P5 carries the TR0 input to the PA0 input of VIA UC1,
via two inverters of UC6. The signal can be disabled by J3, which
enables a permanent connection to GND.

The 1541-II board has a permanent connection to GND at PA0, while
earlier drives have this pin not connected.

> So why connect power to the sensor (on the 1541B) if the output goes
> nowhere??

It does go somewhere, it's visible in the schematics. And it works, a
real 1541B/C drive with J3 open makes use of the sensor and doesn't
rattle the head on a disk format or error anymore.

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