Analog Oscilloscope Repair

Hi everyone,
I have recently acquired an old oscilloscope, its a GW GOS-662 and it uses a cathode ray tube. I'm having some issues with it, in that the trace only comes up for a split second when i turn it on, all the modes, x-y and time/div's work, as I have plugged a sig gen into it and you can see the waveform just start to appear in the different resolutions and also the x and y position knobs work as well. I am about to test all the electro caps, as something may have gone short, which is triggering the protection circuitry. I have also tested all the inputs and the same thing happens on each as well as the internal oscillator. Does this mean that there might be something wrong with the high voltage section that drives the CRT ??

if anyone has any advice to offer that would be great

Cheers,
James

I can't offer any specific advice based on your information. However, in general, your device, as well as old stereos, amplifiers, etc. are subject to aging and deterioration of electrolytic capacitors. .... It's of a long shot, but you might try just allowing the scope to 'burn in' for a day or so .... plug it in, and turn it on .....Maybe the heat will drive out some of the humidity in the capacitors ..... If at the end of the regeneration period, you do not have any positive result, then resort to desoldering the caps ......
I wouldn't try any repair without some sort of a schematic diagram ......

sonicacid said:

acquired an old oscilloscope, its a GW GOS-662 and it uses a cathode ray tube.

Click to expand...

Post a schematic. If no schematic but it uses tubes you still have a chance to fix this. You have a DVM or other, working, o'scope?

Hi Willbe,
I've been searching for a service manual, but i've only managed to find the user manual which has a block diagram, I can post the image of this if you like. I have tested the power supply and I'm getting the right voltages, and I have tested about half of the transistors in the unit. The only thing is with my multimeter I dont think I can see power supply ripple so I've just decided to replace all the power filtering electro caps (1000uF) with EXR caps. And I'm going to leave the unit on for most of the day to see if it dries out the caps. I'm waiting on allen keys from my room mate so I can completely dismantle the unit and further inspect the boards and unfortunately I dont have access to another scope I only have a digitech QM-1320.

Also it doesn't actually use tubes, there are no valves in the unit, just the CRT screen, if that helps.