SC-502 Intensity Stuck at Maximum

Giovanni Carboni

Hello guys,

I am new here and this is my first question.

In my SC-502 scope the intensity is stuck to the maximum value and the knob cannot adjust it. I could reduce the intensity by reducing the beam current but I would like to fix the adjustable control. I measured voltages on the various transistors and checked waveforms but no results. Has anybody ecountered the same problem?



Giovanni: I had this problem and it was solved only after replacing all the high-voltage caps that go between the main board and the high-voltage auxiliary board. C881, C882, C883, C885 and C887. It's not practical to replace one at a time the way the caps span the two boards. You should also check diodes CR884 and CR885. These are relatively low-voltage diodes (225V PIV). Be careful with the large hybrid resistor network R893ABCD as it is fragile. If you have more questions, feel free to ask. I've restored several SC502's.

Bob Haas

Giovanni Carboni

Bob: thank you for answering. I'll take note of your remark, since luckily
I was able to fix it by replacing Q825 (in the process I also replaced Q815
and Q820 which were ok!)

73 Giovanni IZ5PQT