Re: Tektronix 2246 flickering screen, ch2 not working.


I made some photos of traces.
V/div and time base like in service manual.
When I go from A sweep to B sweep I see this:
Trace is on left half of screen.(that was from time I get the scope)
When I turn sec/div 1 position ccw i get this:
6B then is:
Turn sec/div back one position cw I get this:
6B Looks this:
I think that is not a normal behaviour.


Scope behaves like this (previous video was before recap):

I am wondering why holdoff is influenciing traces the way they cuts, and also readouts flickers more or less with different position of holdoff. Also scale ilumination has influence on overall flicker.
Other thing I noticed: There should be grid with dots all over crt when readout is turned on (seen on others video). Here they are present but they are jumping/floating around from left to right very quick.

Other thing is Pin1 of U 802 is Readout horizontal input and looks like this:

Output of U801A Pin1 is:

I am wondering if there is some timing issue, considering strange behavior in b sweep and no stable matrix of dots with readout. Maybe it is influencing also a sweep and overall performance. Where to look for it?
As I said, I am noob in scope reapirs, trying to learn from people who are much better than me. This is for my personal use. Any help like "look in baseline stabilizer" or similar will be apreciated.
Many can say buy a working scope. There are two things: Money (good scopes cost a lot) and It is nice to use equipement that you have reapired yourself.:-)

Also scope behaves very odd when it is cold. It must run for 5 minutes and is operational as on video in this post. For first 5 minutes uncal are blinking, brightness of crt varies. and eventualy it gets as bright as it shold be. There are random brights up during first 5 minutes.

Join to automatically receive all group messages.