16 May
2010
16 May
'10
12:02 p.m.
Many thanks for the reply. I am not an electronics expert unfortunately, but
Alas sometimes I forget that not everyone had a mis-sepnt shildhood...
will look at your suggestions. One thing I did
(perhaps wrongly) was measure
the voltage with one probe connected to the casing, not to the other pin on
This problaby is not the right thing to do. The point is that you need to
be able to pass a crurrent through the positioner coil in either
direction (one way will exert a force to move the heads towards the
spindle, the other way will exert a force to move the heads away form the
spindle). Now if you had one side of the coil grounded (same voltage as
the chassis) yoy would need power supplies of both polarities wrt ground
to be able to do that.
What is more commonly done is a circuit based on what is called a 'full H
driver. Basiecaly it means both sides of the load (the coil in this case)
can be driven. If one side is pulled towards ground tand the otehr side
to, wayu, +12V, the heads moce one way. But if the first side is taken to
+12V and hte second side to ground they move the other way.
If oyu measure the voltage wrt ground on one end of the coil you are,
effectively, only testing half the circuit. There could still be a fault.
the cable. I will try across the two pins to see what
that is like. I don't
have a DC supply I can use to "blip" the coil, unless I can press the PSU
Sure you do. I bet you'd get some movement using a small battery. P
from my MicroVAX II into service for this? Is there a
danger I might pass
too much current and burn the coil?
There is, which is why you 'blip' it. Actually, a battery is probably the
safest, a primary (non-recharageable) 9V battery is not going to supply
enough current to do much damage.
-tony