unreadable HP cartridges

[Tony Duell]

> Correct. I can't remeber if it's 2 tracks or 4 (I think the latter), but 

No, I was wrong. It's a 2 track device. And it's clear it uses one track 
and then the other, it doesn't stick '1's on one track and '0's on the other.

The signals on the drive connector (20 pin card edge) are a few power
lines, the 2 ends of the motor (there is no motor control circuitry in the
drive), the outputs of the op-amps for the EOT and Tacho sensors,
TTL-level write data, write gate and track select, the output of the read
preamp, an LED drive signal (if the drive has an in-use LED) and a
power-OK signal to prevent glitching the tape at power-up/down. 

-tony