Tektronix 2235 Volt/Div Malfunctiog on Some Settings

[gmcjetpilot]

Channel A on 1, 2 and 5 volts/div are ok.

Not working is 20m, 50m, .1, .2 .5, 10, 20 and 50 volts\/div is not working, zero volts. Again 1, 2 and 5 volts are OK.

Channel B is fine.

Unrelated may be is the probe connection is intermittent when wiggled. Dirty? Bad probe connector.

I have owned it for 15 yrs always reliable, clean, but not used for many many years. Always stored inside home. I noticed this issue last year but only needed one channel. Recently needed two channels and got the job done on 1 volt/div... However I like to fix it.

Ideas. I read other threads... Is the service manual on line?

[George Edmonds]

Service manual is here

https://w140.com/tekwiki/wiki/Main_Page

G Edmonds

[David Hess]

When you say not working, what do you mean?

Are they the wrong sensitivity?  Is there no signal?  Is the signal corrupted?

My guess is that the cam switches are not making good contact anymore.  The leaf for each cam switch can be bent with tweezers to restore good contact.

[gmcjetpilot]

WELL WELL I did something. 

I opened it up, removed the cover over the front board, which requires removing one header (yellow wire aft) and saw the Channel A Volt/Div selector mechanism. Contacts clearly visible. I blew compressed air around to dust it out (it was pretty clean).

I rotated the selector and saw contacts open and close on traces. Decided to apply a little squirt of D5 Deoxit on contacts that were open and exercised selector, repeating for each set of positions. I put it back together.

No trace now on either A and B.  Beam finder works. Back light, it powers on. Just no trace. I did all the usual things with intensity and position to find the trace.  Again scope working except channel A, 5 of 8 volt/div positions not working (reading zero volts when signal applied), but OK in 3 position (1, 2, 5 v/div).
 
I am going to let it dry out over 48 hours and hope it will self heals.

I am 99.9% sure I put the header back correctly. I was careful, but clearly I did something wrong. I never had D5 go sideways. I applied sparingly. D5 is great in contacts and no doubt some got on board, but it is safe in my opinion. We are talking about a 20-30 yr old piece of test gear.

If you have ideas or want to admonish me feel free.... . I am sure there is a thread somewhere that says never clean the contacts with D5. Ha ha.

[David Hess]

The cleaning of the contacts is done by closing the contact on a piece of non-clay paper, like a 3x5 card, soaked in solvent and drawing the paper out.  Spraying with anything will make a mess.