Oscilloscope not focusing (Telequipment DM63)

I have a Telequipment DM63 CRT storage oscilloscope, and it has been working correctly for the past few months.

Usually after 5-10 minutes to warm up, I have a sharp trace on a dark screen, but recently it has stopped focusing correctly. The screen now stays fully illuminated indefinately, and the dot is stuck as a 1/4 by 1/8 rectangle. The intensity and astig controls appear to be working correctly, but the focus does not appear to be doing anything.

I've found a couple of old threads on other forums suggesting that the issue is likely to be a damaged resistor between the power supply and the focus control, or noise from the power supply itself.

Thanks in advance for any ideas or suggestions.

Picture of Oscilloscope not focusing (Telequipment DM63)
The telequipment manuals are downloadable. It will be a dry joint or a burned out resistor.

caitlinsdad5 years ago
That's interesting, can you use the scope on itself to diagnose the problem?
The Skinnerz (author)  caitlinsdad5 years ago
It is still just about useable to pickup simple waveforms, but accurate measurements are out of the question. I should have time to take the side covers off and have a look inside tomorrow.

If necessary I can get hold of another oscilloscope, but I'll see if there are any obvious hardware failures first.