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.

 

[Tony Stewart]

It seems like the tube focus is out of alignment. Get the manual. otherwise https://repair.wiki/w/CRT_Picture_Adjustment_Common_Issues_and_Fixes

 

[RKA]

It seems like the tube focus is out of alignment. Get the manual. otherwise https://repair.wiki/w/CRT_Picture_Adjustment_Common_Issues_and_Fixes

I've managed to get the image almost right now. I still think something isn't quite right though as there's an occasional wobble or flicker in the image and sometimes when I turn the machine on the crt displays no image at all. I've set the vertical resolution to 1v per div and the 1v peak to peak test signal is taking up 2 divs confirming my suspicion that vertical scale is somehow off. The scope has a time and date showing as well which disappear out of the screen size down the bottom as the scope warms up. I haven't worked out wether the horizontal scale is calibrated, I'll do this tomorrow when I'm back at the workshop. I've been unable to locate any documentation on this scope, it seems to be a bit of an oddball

 

[augustinetez]

Can you take a picture of the whole front of the oscilloscope, many scopes of that era were rebranded under other names so a manual might be available under an alternative name.

 

[rjenkinsgb]

It sounds rather like the EHT supply to the tube is low?

That means less acceleration applied to the beam, so it has more time between the deflection plates and is affected more than it should be with the correct voltage.