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Electronics => Repair => Topic started by: Smokescaped on April 22, 2024, 02:29:44 am

Title: Tektronix 760A troubleshooting - Excessively large trace (solved)
Post by: Smokescaped on April 22, 2024, 02:29:44 am

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.

Title: Re: Tektronix 760A troubleshooting - Excessively large trace
Post by: BlownUpCapacitor on April 23, 2024, 06:33:15 pm

reduce the intensity

Title: Re: Tektronix 760A troubleshooting - Excessively large trace
Post by: BlownUpCapacitor on April 23, 2024, 06:43:58 pm

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.

Title: Re: Tektronix 760A troubleshooting - Excessively large trace (solved)
Post by: Smokescaped on May 02, 2024, 05:54:24 am

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.