ATM platform drive problems

["Jan van Gastel" <jhm.vangastel@wanadoo.nl>]

Last night I wanted to use the eq. platform for my 20" for the first time.
It is driven by a 12 V DC motor and a pulse width modulation (PWM) circuit
with a handpad for control (so not a stepper, to prevent vibrations) and a
threaded rod. Inside the house everything worked perfectly, but last night
the drive failed. The motor wouldn't run. It was not the motor itself
because when I connected it directly to the 12V, it ran perfectly (but too
fast and uncontrolable without the circuit).
So it was the PWM circuit that failed. It worked very well inside my house
and when I tried again (inside) this morning it worked perfectly again.
Could it possibly be the low outside temerature (-8 degrees C or, if I
calculated right: 17.6 degrees F)? The PWM circuit I used is under the link
below. I would appreciate someone with more knowledge of electronics taking
a look at it. Maybe one of the components fails at low temerature?
It is at:
http://www.circuitsonline.f2s.com/circuits/view.php?cat=modelbouw&sch=02

Another point is the play in the connection of drive arm and threaded rod.
It makes it difficult to center an object in the FOV. The slot in the
aluminium plate in which  the drive-arm can move abit, is two mm wider then
the diameter of the drive arm to prevent the rod from binding. Maybe this
could be a bit less then 2 mm, but maybe there are other solutions, without
any play. If so: i would like to hear.

Thanks in advance.

Jan
http://www.geocities.com/janvangastel/Astronomy/