Thanks Dwight for some insights into rectification. Always fun to learn more. And thank you Dave for the 7218 test wiring. That is what i did minus the caps for bench testing
As I wait for the 7812 in strong hopes it fixes the dead board, maybe I can pick your collective brains on the nonlinearity board:
Shouldn't somebody who can actually understand the magical schematics be able to kindly find a small set of parts that creates the voltage slope that makes the crt beam go from left to right. And whatever determines the speed / slope of this voltage increase needs to be replaced. And as we can exclude the caps, what is it that changes horizontal coordinate on the beam, if it is not a cap?
I feel its a capacitor but while I have quite a bit of hands on experience with CRT circuits, its still a bit, err, by intuition and tests rather than look at circuit and really get to grips with the design.
So the cap I have identified isn't based on 'real circuit investigation' rather a starter for 10.
The zimmers does have the scope traces for each part of the horizontal deflection circuit and checking them for test points 13 to 17 would be worth while, but as I said, the horizontal deflection circuit is also used as an oscillator to drive the HV coil for the CRT's anode and thats High Voltage with a capital H (even for me and I work with 400kV circuits) SO BE CAREFUL
This https://www.eeeguide.com/television-...ction-circuit/ gives a bit of a guide to how this part works (though its not the same circuit at all)
1. The scan coils (horizontal coils) - I suspect the easiest way is by substitution.
2. C28. This should be a 10uF NON POLARISED capacitor (the red 'block' capacitor in your photograph).
3. C25. This is the yellow tube capacitor near C28.
4. CR17. This is a diode you can test with a multimeter.
That’s a shame.
However, if you go back to my post #71 it was always a possibility...
Some machines are easy to fix, others not so, and others are just pigs! A few members I know have had pigs to repair and, to their credit, they have persevered and chased all the badness out of their machine. After that, it has been fine!
So don’t give up - have a few slices of turkey, some wine of your choice and regroup back in 2022.
I learnt the hard way when I was twenty something about what the small bit of plastic was that came with the probe - it protects the circuit being probed from the ground ring surrounding the probe (as I shorted the collector (metal can) of a PNP transistor to ground via the probe and burnt it out). This was on a home-built theatre lighting controller. Needless to say we had no more light that evening until a replacement arrived!
It is unlikely that you have damaged the transformer. I would disconnect the power cable from the PET main logic board and disconnect the power cable from the monitor and measure the transformer secondary voltages with your multimeter on AC volts.
Examine the top and bottom of both the PET main logic board and monitor board for signs of burning. There must be some evidence of it somewhere.
These are relatively simple tests to perform...
Have a good Christmas.