Re: How to troubleshoot a faulty 7B50 timebase

Thierry Delaitre

thank you.

I can find a sweep at the base of the Q784 (output driver) and nothing after.

I have correct voltages for the line voltages -15V and 50V

Other voltages are as follows (with a time dev of 1ms):
- Collector of Q774: 5.6V instead of 6.41V
- Collector of Q764: 6.6V instead of 6.42V
- Emitter of Q794: 11.5 instead of 7.22V
- Emitter of Q784: 6V instead of 7.33V
- 13.1V across C799

I've also tried to disconnect C799 just in case if it was leaky but it is still the same

I've also checked the resistors (in-circuit) around Q774 and Q784/Q794 and none have exceeded their values.

Does it mean that one of the output driver Q784 and/or Q794 is leaky?

Should I replace them with a 2N4122 or are there any other equivalents that are easier to source?



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