Unilab Oscilloscope 032.601 showing no trace

[MontyTheGreat10]

A few days ago I picked up a vintage CRT oscilloscope at a car boot sale. It is quite a simple model, but I was going to use it with synths and stuff. When I turned it on, though the power LED turned on and the transformer started humming, there was no trace on the screen, however I adjusted the controls. Later, I had a poke around inside, and found out that all of the potentiometers were working on the front panel, and that there were no broken traces on the board. I also confirmed that the heater on the CRT glowed when the power was turned on, showing that the CRT was probably working. My guess is that the focussing circuitry is broken, and I would be very grateful with any help people can give me on this matter. I have included a schematic. https://elektrotanya.com/unilab_032.601_educational_oscilloscope_d7-200gn_sch.pdf/download.html#dl

[MontyTheGreat10]

bump2

[MontyTheGreat10]

Reply for a poor broken oscilloscope?

[ambrosia heart]

" I also confirmed that the heater on the CRT glowed when the power was turned on,." thermoionic emission OK.
Accelerating grid voltage must be checked.

Check ALL circled components. Caps, diodes and opamps
replace.  Components are not expensive compairing labour
cost. 

See photos.

[MontyTheGreat10]

Thank you! I will start with checking all power supply voltages, then I will look at the control grid and anodes with the oscilloscope in XY mode, to see if I can get a dot to appear. I will then check the time base circuits, and will follow your advice if it doesn't work properly.

[jdragoset]

If you can't get a dot, keep in mind IC 4 is an optical isolator that appears to control blanking.
Fortunately the CRT voltages are not terribly high (+- 500VDC) to use a DVM for testing. , standard hands off testing for safety.

[MontyTheGreat10]

I may actually just try unplugging the control grid of the tube, and if it comes on in full brightness mode, I will know that the control grid circuit is stuck, causing the tube to appear off. If that doesn't make a difference, I will know that it is probably one or both of the anodes, and will test their voltages.

[JFJ]

Have you tried adjusting R46, the Set Blank variable resistor? It can usually compensate for the aging opto-isolator in the CRT blanking circuit.

[MontyTheGreat10]

I think I may try that, before unplugging the control grid, so thank you for saying!