Electronics > Repair

Tektronix 760A troubleshooting - Excessively large trace (solved)

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Smokescaped:
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.

BlownUpCapacitor:
reduce the intensity

BlownUpCapacitor:
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.

Smokescaped:
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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