Yet another idea for recovering the data from Series80

[Tony Duell]

> >What I would do (and alas it needs a 'scope would be to remove the R/W 
> >chip and connect the differential inputs of the 'scope to HC and H0 
> >(say). Run a recorded, but unimportant 'scratch tape' through the thing 
> >and see what signal you get. Then design a differential amplifier to 
> >bring it up to the sound card input levels. 
> >
> >The preamp schematic from the 9815/9825 tape drive might be a start. Does 
> >anybody know if those drives are tape and track compatible with the 85 
> >drive? 
> 
>    They DO use the same tape so they must be compatible. I don't know about

That is, IMHO a non-sequitur. These tapes are not pre-formated, so 
there's nothing in the blank media that determines the track positions. 
OK, we know both are 2 track drives, we know the full width of the tape 
can be used by the head in the drive (the tape is not turned over or 
anything), but that doesn't necessarily imply that the track position and 
spacing is the same. It is, however, very likely to be the case.

> the track spacing but I would think they would be the same. It should be
> easy enough to check with some MagnaSee. I THINK that's the name of the
> liquid that you put on mag tapes/cards to see the magnetic tracks. I have a
> can of it around here somewhere but no idea where it's at at the moment.

I am still looking for a can of that stuff. 

> >Could you not design your own motor controller? It's 'just' a matter of 
> >controlling the motor voltage to get the right frequency output from the 
> >tacho sensor.
> 
>     It's a servo loop so I don't think it would be that easy. You'd have to
> have the correct response times and all that to make it work properly. And
> remember that these motors have both a high spped and normal reading speed
> as well as reverse so your controller would to be capable of handling all

Yes, but you don't need that. Versallis (?spell) just wants to read the 
tape. He doesn't want to do high-speed searches or rewind or anything. so 
the problem is a lot simpler.

If you could use the 9825 tape drive, then I'd grab the controller from 
that machine too. From what I remember, the motor speed control is all 
done in hardware (unlike the 9815, where there may be some 6800 firmware 
involced, but actually, again, I _think_ it's all hardware). Use that to 
control the motor (it's easy to write the correct values to the I/O 
locations using just about any other machine, the bus is pretty simple), 
make your own head amplifier and read the signals with a PC soundcard or 
whatver.

-tony