[Test-Equipment] Tektronix T935A Scope - seized knobs

[Chris Trask]

>
> Tektronix T935A Scope.
> The center red "VAR" knobs on both Chan A & B Volts/Div Amp. knobs have
> seized.  In other words, either red knob won't turn at all.  What is the
> cure?  Do I have to open the cabinet to work in a penetrating oil on the
> shafts from the inside?
> Or, Just remove the knobs and try to un- seize the shaft from the outside?
> Or ?
>

    I had to tackle this problem on a Heathkit high voltage variable power
supply, and it will require a good degree of patience.

    It will help greatly if you can apply penetrating oil at both ends of
the shaft bushings.  Once a day, every day.  Also, lubricate the wipers on
the actual control, whether it's a potentiometer or a switch.  Before each
application of the penetrating oil, gently try to rotate the shafts.  DO NOT
FORCE THEM.  When they begin to work free, watch the control wipers and make
certain that they are not stuck themselves.

    I also had to do this recently on a rifle scope mount where the two
screws in the rear ring had been overtightened.  I spent a month using
penetrating oil and had to resort to using a 1/4" pneumatic ratchet, slowly
turning up the air pressure.  Fortunately, the screws came out with no
breakage.  I got the mount and the scope (a Lyman All-American X4) for $10
in a thrift store.

Chris