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IF we are back to horz lock issues, a few things to consider.
AGC, keyed agc is always good for tough dogs. Make sure you check C405 a
.22 uf cap used to filter the AGC.
Note where the AGC pot is set (top of chassis near the chroma section). when having lock problems try adj just a bit if no improvement put it back to the starting position.
the deal is if the AGC in noisy or incorrectly set (cap or pot setting) then the IF amp gets whacky and does odd things with the signal, clipping etc..
this results messed up sync signals (they are the 1st thing to get clipped in the IF amp).
The normal approach to checking this would be to attach a bias box to the AGC line and manually provide the bias needed for the IF amp. Since you don't have a bias box we have to assume the most likely suspect (after the tube) and go right to the AGC filter cap.
An alternate to the bias box is a scope on the agc line set to read DC. adjusting the pot should raise or lower the DC bias from the output of the AGC supply AND the voltage should be clean DC with no "grass". the grass is a result of the loss of filtering.
I presume you have replaced the C405 in on of you mass recappings already so this may not be an issue.
Another possibility again assuming you are still having issues with horz hold and the issue is a very critical hold range of the pot (only a few degrees of adj from flopping one way to sync to flopping the other (which is NOT what you have described so I only mention for future reference) is the 68k resistor that p's with the horz hold coil. I presume its a Q killer to soften up the peak of the coil.
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