Vector and ST506 (was ST506 and-or ST412 hard drives

[Tony Duell]

> Apparently there is a cut and jumper modification which can be made to the
> ST506 circuit board to bring the /INDEX signal to the interface constantly
> even when the drive is not selected.
> 
> Once I get a ST506 drive I will find and make the modification.  Assuming I
> can get the ST506 to work, I will try making modifications to ST225's or
> other more common hard drives.

It would eb useful to find out the modifaction (to either an ST506 or 
ST412) anyway. One of us with the approriate schematics (I am pretty sure 
I have both...) can then work out what's going on, what signal is tapped 
off 9and where), and what pin it's brought out to.

My _guess_, and it is just a guess, is that the index siganl is tapped 
off immediately before the output driver (which normally only feeds the 
index signal onto the control cable (34 pin) when the drive is enabled), 
and this siganal is wired to one of the many unused pins on the data (20 
pin) connector. That way the controller can always seel the index signal 
of all the drives in the machine

-tony