Tektronics 2246 acting funny on CH2 - floating

[tkamiya]

I have a Tek 2246 I've been working on for few months, on and off. 

This scope works fine with exception on one thing.  Channel 2 acts out after few minutes from cold start.  The trace goes up and down by about 1 unit on graticule, sometimes slowly, sometimes quickly.  Sometimes it almost forms a wave form.  The behavior does not change with voltage divider setting or horizontal sweep setting.  (of course, scan speed changes but vertical movement stays the same)  On Ch2, I can actually make measurements and they are accurate.  It's just that it acts like its ground is floating.  It behaves the same with input grounded as well.

I've replaced a vertical control pot on the front screen.  Cold sprayed everywhere.  Tapped everything with back of screw driver.  Nothing I did changed behavior.  It is acting as if there is a cold solder joint or intermittent connection somewhere but I am unable to find it. 

If anyone has any ideas, I'd be thankful of hearing about it.

[Rollin Hand]

I have had some similar experiences. Unless you have a lot of free time and nothing better to spend it on my guess is that chances are you will waste much time and not get far. From a practical point of view I would suggest finding a pro.

[tkamiya]

That is very true.  This is only a 100MHz scope and its monetary value is quite low.  I've also spent way too much time working on it.  Continuing like this is simply....  crazy!     However, I do this for fun and relaxation.   

So...  if you have any unwanted eBay wins, please contact me privately.  I will properly dispose of them for you.