Hi Richard,

> Does anybody the difference in circuit design that would cause this
> effect Can I easily modify my newer A-155 to behave the same way

Newer 155's have a small mod on them, which I believe is to stop it
stepping more than one step when manually clocking it (and it's also
the thing that stops you clocking it very fast!). Underneath 'Board 4
(Controller Board)' (one of the small ones), on your newer 155 you
should see a capacitor and resistor soldered together and bridging a
couple of pins on an IC. I suspect this mod may be what stops newer
ones behaving this way. I know Bakis (for one) has removed this mod
on his 155's, so perhaps if he is listening he can quickly try
clocking it with a sawtooth to see if it does clock 'randomly'
(It'll save me getting my soldering iron out, but I will carry on
looking at it to see if I can figure the exact mechanism out...)

Tim