5 Feb
2006
5 Feb
'06
4:04 p.m.
At least, I
*think* it was the 1541. Same drive that had a stupidly
underrated power supply that tended to blow with the slightest
provocation.
Yeah, it was the 1541--and didn't the Apple ][ drives use the same
technique of "step into the stop until you're sure you've hit bottom"?
But then, some dot-matrix printers used the same technique for zeroing the
carriage. If you had the carriage powered by a DC servo instead of a
stepper, you could even monitor the motor current to see when you'd slammed
into the stop.
The infamous LA36 does this, but I thougth it detected the end stop by a
lack of pulses from the shaft encoder on the back of the motor.
We had an LA36 in the lab where I worked. The plastic key in the carriage
drive sprocket broke, and the motor therefore didn't stop when the
carriage hit the end stop, it just kept on turning very slowly against a
heavy load (the friction of the sprocket on the shaft). The result was
the motor got hot enough to burn the insulation off the windings, and at
that point the carriage motor fuse blew.
Well it didn't take me long to track that fault down. The motor drew 4A
from a bench supply with no mechanal load. The only
problem was that DEC
charged some ridiculous price -- about \pounds 150 I think --
for a new
motor. Since research student's time is not worth much, another chap and
I spent an afternoon rewinding it.
A few years later, that LA36 was scrapped. No I didn't take it (one of
the few DEC items I didn't grab), but I did take some bits out of it. I
still have the carriage motor with the 'rewound by ARD and AMG' label on it.
-tony