[Test-Equipment] Tektronix T935A Scope - seized knobs

[cemilton at aol.com]

Could be the knobs have been pressed "inward" to the extent they are seizing on the mounting nut.  Try loosening and backing them out about 1/16".  Just another idea.

ymmv

73
Chuck
W4MIL




-----Original Message-----
From: Chris Trask <christrask at earthlink.net>
To: Discussion of Electronic Test Equipment <test-equipment at mailman.qth.net>
Sent: Wed, Jul 21, 2010 8:53 pm
Subject: Re: [Test-Equipment] Tektronix T935A Scope - seized knobs


>
 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
upply, and it will require a good degree of patience.
    It will help greatly if you can apply penetrating oil at both ends of
he shaft bushings.  Once a day, every day.  Also, lubricate the wipers on
he actual control, whether it's a potentiometer or a switch.  Before each
pplication of the penetrating oil, gently try to rotate the shafts.  DO NOT
ORCE THEM.  When they begin to work free, watch the control wipers and make
ertain that they are not stuck themselves.
    I also had to do this recently on a rifle scope mount where the two
crews in the rear ring had been overtightened.  I spent a month using
enetrating oil and had to resort to using a 1/4" pneumatic ratchet, slowly
urning up the air pressure.  Fortunately, the screws came out with no
reakage.  I got the mount and the scope (a Lyman All-American X4) for $10
n a thrift store.
Chris
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