1972 Motorola CRT Monitor - Losing Focus

[MightyFrame]

Thanks to many of you here, I was able to successfully change a bad CRT on this 1972 Motorola Chassis that had "gone to air".

But now, new problems arise, apparently with the circuitry that drives the video signal on this chassis.

With 50-year-old components, I fully expect several, if not many, capacitors (or any components) to go bad. But which ones?

The Symptoms:
On first power up, I had a picture, but it appeared "smeared" and harder to read than I had hoped.

FirstPowerUp.jpg

After about 5 minutes, the image has seriously degraded, and while the smearing seemed to go away, it gradually was replaced with what appears to be a lack of focus, where each character now apppears to be a circular blob, and while it was hard to recognize them at the beginning, now it's impossible.

LostFocus.jpg

For reference we're looking at here are somewhat random characters generated by this ancient and rare computer terminal, which when properly displayed, should resemble this:



So, my question is this: What area of the driver circuitry controls these aspects? There is no "focus" control marked as such, and even if there were, I suspect that I shouldn't touch it, as this change occured without any adjustment. All of my research so far suggests that one or more components are failing, and any adjustment won't help until the component(s) is/are identified and replaced.

Thankfully, based on this schematic for this chassis, the circuit seems relatively simple:

Motorola Monitor-TV Chassis Schmetics

I'm hoping that a few of you vintage TV experts here could help me isolate the proper area of the circuit to start testing and replacing components for symptoms such as this.

FWIW, I fully expect, and will fully heed, every and all warnings about safely and completely discharging the high voltage section of this assembly before touching anything else. Especially since it seems likely that this problem is indeed related to the high voltage section of this circuit.

Thank you all for your kind and knowledgeable help.

Best,
AJ