Firstly, I want to express my gratitude for all the assistance and guidance. Hugo and Dave you really helped me out - thank you!
Long story short - after confirming all the transformer wiring was correct, etc. the theory discussion you folks were having led me to do a bunch of reading on how the CRT actually works which led me to the horizontal width coil as an area of interest for my problem. That then led me to C724 as the likely culprit. I replaced it and it's all working perfectly now!
Thanks again. I learned a ton!
That is good that it appears fixed, but....
Are you sure you meant to say C724, or is that a typo ?
The fault you had on your screen cannot have been caused by a faulty C724.
This capacitor, with is series resistor, is merely a damping component across the width inductor and linearity inductor. Any failure in that capacitor cannot cause the under-scan you had with the full wave line power ripple modulating it.
The likely explanation for your fault, consistent with your meter measurements, was that too low an AC voltage was being fed to the VDU, because it was being fed from the wrong tap on the transformer, or for some other reason the AC voltage was too low, like a high resistance connection, possibly for example in the soldering to the pcb pins or in the plug assembly that introduces the AC to the VDU.
So, although your fault appears to be fixed now, the only logical explanation is that it is an intermittent fault and it will therefore return later.
This is another interesting lesson in electronic equipment servicing: The faulty part that you find has to cause an effect that is consistent with the fault that you are seeing based on the circuit's theoretical operation, before the repair of that fault can be considered complete or successful.
What can happen with an intermittent fault, it can vanish at any time. So if you are working on a vdu or any piece of equipment and you replace some part that is completely unrelated to the fault and at the time the fault vanishes, you re-power the set, the fault has cleared and it leads you to falsely conclude that you have found the defective part and repaired the set.
