[Test-Equipment] Tektronix T935A Scope - seized knobs

[Richard Knoppow]

----- Original Message ----- 
From: "Barry" <n4buq at knology.net>
To: <test-equipment at mailman.qth.net>
Sent: Thursday, July 22, 2010 8:46 PM
Subject: Re: [Test-Equipment] Tektronix T935A Scope - seized 
knobs


>
>> Found no binding on the knobs. I had to open the cabinet 
>> and look
>> internally.
>> Followed VAR knob shafts to 1k pots on board - Found 
>> seizure to be in 1k
>> pot bushings.
>> Sprayed bushings lightly with Chemtronics "Trol-Aid" from 
>> 1970's.
>> Worked in lube and they slowly loosened up enough to turn 
>> from front red
>> VAR knobs with just fingertips.
>> Will re-assemble tomorrow - how much should I charge 
>> myself ?
>>
>> Back to tube radios,
>>
>> bob...w2ami x wn2ami 1962
>
> I had a similar thing occur on a Tek 465B I recently 
> acquired (okay, "won" on eBay).  The "Focus" pot was 
> extremely difficult to twist.  I worked in some DeOxit 
> (yes, I know, it's not exactly the correct chemical for 
> the job but it worked).  The shaft eventually was very 
> free to turn; however, about a week or two later, it is 
> beginning to show signs of hardening lube again.  Looks 
> like a more permanent solution is to disassemble the pot 
> and clean it correctly.
>
> 73,
> Barry - N4BUQ

     I have a similar problem with the band indicator on 
a -hp- 606A. This is a pointer hinged on a shaft and 
operated by a cam and returned by a spring. When I got the 
generator the pointer wouldn't move. I applied Liquid Wrench 
to the end of the shaft and after several days it loosened 
up. Now its sluggish again. The problem is that to get to it 
for a proper cleaning requires removing the front panel. I 
will eventually have to do this. The problem with Liquid 
Wrench, WD-40, Deoxit, etc., is that they are not real 
lubricants and are pretty volitile. While they may soften 
old grease temporarily they don't really replace it with 
anything and the grease will harden up again when the 
solvent evaporates. Sometimes there is no easy way to do a 
job and trying to save trouble just makes it harder.
     As far as the sticky pots go it depends on whether its 
the shafts sticking in the journal or if its the wiper 
sticking to the resistance element. If the shaft then 
running a little very light silicon oil into it may fix it 
permanently. If the wiper you need to open the pot and get 
some cleaner into it. Sometimes a light grease like 
Tuner-Lub will work on old pots but most were intended to 
run dry.

--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com