Leader 8042 oscilloscope strange crt fault

[RKA]

Hello,

I'm new to this forum, I'm hoping somebody here can send me in the right direction.

I've obtained a Leader 8042 dual channel 40mhz oscilloscope. It has a rather odd issue where the image seems to have a lot of vertical noise on it. The image also seems to blow up too big for the screen. From what I can see the noise appears to be a fixed frequency.

The noise appears on both traces and I believe it to be in the crt circuit as it appears on the date and cursor as well. When the scope is turned on the image appears correct very briefly and then blows up and gets the noise on it.

I have been unable to locate any documentation on this scope, I'm kind of at a loss where to start as this appears to be quite a complex scope. I'm hoping someone recognizes the issue.

Thank you for your time

 

[RKA]

I've made a slightly sharper image of the fault. This is with ch1 connected to the test input.