Tektronix 465 CH2 issues

[Microgiant]

Can someone please point me in the right direction?

I am repairing a Tek 465 that had several problems. So far I have rebuilt the power supply with all new capacitors, a new bridge rectifier and 3 new transistors. All voltages are now as expected with low ripple. I then repaired an issue with A trigger not working.

Now I am am stumped by an issue with channel 2 vertical. I assume its a vertical issue because its missing about 50% of its amplitude and the square wave is ramping. I initially assumed it had to be part of these circuits since the problem is only on channel 2 however I can find zero issues on the Vertical Preamp board or Vertical Switching. Its originating somewhere else.

Someone has attempted repairs on the scope before me and they were ham fisted. The delay line was roughed up and had to be soldered to the vertical preamp board. I cleaned this up the best I could and Im not sure if it had anything to do with my problem, I dont see how it could affect anything.


https://groups.io/g/TekScopes/photo/253550/0?p=Created,,,20,2,0,0

I will cross post to the TekScopes group to get some other eyes on it as well.

[Wallace Gasiewicz]

Usually these problems in many scopes are in the input. In this scope the attenuator is a likely suspect
I do not know if you checked this specifically.

Wally

[Microgiant]

The only attenuators I am aware of are located on the vertical preamp right after the BNC inputs. I have tested the complete vertical preamp including all inputs and found nothing wrong.

After testing the vertical preamp board and switches and finding nothing wrong, I was confused so I second guessed myself. I thought I must of missed something so I took a second working vertical preamp board complete with attenuators and vertical switches and swapped them and the problem was exactly the same.

[David Hess]

Half amplitude on one channel only usually means that there is an open along the differential signal path up to the vertical channel switch.

[Microgiant]

Hi, Yes, thank you, it turned out the "open" was one of the two AC/GND/DC leaf switches. Here is the thread that solved the issue.

https://groups.io/g/TekScopes/topic/76848756?