Quote:
Originally Posted by old_tv_nut
A DC current would shift the raster sideways, not wrap it around.
Bob and I have started an email exchange. I think the problem is somewhere around the sync discriminator or its inputs.
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This is what Wayne wrote to me................
Thanks. First let me say I never have trouble-shot one of these, so I can only make suggestions based on general principles.
Let me know: Do you want to proceed by email or on Video Karma? If VK, please copy the following there. It might be the best way to get someone with particular experience to help.
Have you tried subbing v11 and V12? Can you poke around this area with a scope?
The left half of V11 separates the sync. I’d guess it’s OK because you have vertical sync.
The right half of V11 is the phase inverter. One polarity is on the anode and feed the vertical circuit and the upper half of the sync discriminator.
The opposite polarity should be on the cathode of the inverter (R74) and feeds the lower half of the sync discriminator. A scope should show equal and opposite polarity waveforms at left sides of C58 and C59.
There should be a horizontal waveform of some kind coming through C61 and shaped by C60 and R79. I don’t know if it should be a pulse or a sawtooth wave or what on C60, but I’m thinking sawtooth more or less. If I understand the circuit correctly, the pulses from the sync phase inverter should be occurring in the center of the sawtooth, creating a neutral control voltage out of the sync discriminator and making the horizontal sweep line up with sync.
If V11 and V12 are good, I would check components in this area. Anything connected to right half of V11; anything connected anywhere on V12.
(FYI Vert sync is fed to the vertical oscillator through R75 and the following R/C integrator components to filter out the H sync and transmit a vertical pulse.)
Regards,
Wayne