Electronics > Repair

Tektronix 760A troubleshooting - Excessively large trace (solved)


Thanks everyone who helped with capacitor advice in the other thread, I successfully got the machine running.

Bad news is the trace is enormous.
Playing with the limit-screw adjustment for focus simply changes the sharpness of the 'trace' without changing its size.
Once again I'm hoping for a helpful push in the right direction to begin troubleshooting this.

Greatly appreciate any feedback. Cheers.

reduce the intensity

On second thought this looks like a HV failure. First measure all voltage rails, make sure they're all fine.

Measure voltage across C34 as well. Should be around +100v.

Measure across R49. Should be 115v.

Measure at pin 2 of J3, the voltage should vary between -15 and +100v depending on the setting of the astigmatism adjustment.

Measure J11. Warning HV here. Report back.

Thanks mate, reporting back!

It's fixed and the problem was caused by bad resistors in the focus circuit.
R3-R4-R5 were all significantly out of spec. I replaced R1 and R2 while I was there.


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