Firing up the pdt11

Tony Duell ard.p850ug1 at
Mon Oct 12 10:11:47 CDT 2020

On Mon, Oct 12, 2020 at 4:04 PM Chris Zach <cz at> wrote:
> > In a 'real' RX01, each sensor LED (track 0 and index) has the cathode
> > grounded and the anode connected to +5V via a 68ohm series resistor.
> > If you measure the voltage across the pins with the LED disconnected
> > (or if the LED is open-circuit) with any reasonable meter, it'll read
> > 5V. The meter will not draw enough current for the resistor to drop a
> > noticeable voltage.
> Ok, that makes sense. Is the resistor on the board or on the drive wire
> harness somewhere?

I'm pretty sure it's on the PCB.

> I'll jumper the disk 0 sensor into my test board here (actually just the
> extender board from another PDT11) and see what the voltage looks like,
> then compare it to the same spot on the second drive.

I'd look at the voltage on each pin of the LED in the 3 other sensors
(index and track 0 for both drives)


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