Aaargh disc-magnet

I hope someone here has a l-o-o-o-n-g memory
I just wired up some old 2" diameter, 100 step/rev, Escap disc-magnet
steppers. They simply refuse to half step, When I go to a half step position it doesn't lock, I can easily turn the motor half a step either way. Fantastic performance full stepping but not half.
Anyone remember if this is a feature of older disc magnet motors?
P532 258 004 17
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Found it. the comparator was drawing more power off the resistor divider than expected and I was only feeding it 0.1A rather that the 0.8A intended. Then I had a bug in the code, then I kept winding up the speed to see how fast I could go.
This is one hot motor, not bad for an oldie. I got it up to 1380 half steps/second at a mere 16 volts. It balked when I tried 2000 but started with a bit of a push so all it needs is an acceleration table and the sky's the limit. Most pleased :o)
I'm using a circuit I found on the Jones Stepper site with a few extra bells and whistles of my own, driving off an IBM parallel port using the timer interrupt. Here's a pic
http://www.robinhewitt.net/discs.jpg

position
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