HP 85662A Display Flickering (8566B) (SOLVED!)

[pnv57]

Last year I bought a 8566B and display and it didn't work. I recently bought another pair (together), and fixed a YTO unlock by swapping the YTO loop, FM coil driver, and main coil driver over (all three were faulty). It been working for maybe two weeks now, and I use it quite a bit. One day I turn it on, and the display is flickering wildly, where everything on the screen kind of falls into a point in the center repeatedly. If I change the status of traces A and B (view vs blank) the frequency of which the flickering happens increases (both blanked) and decreases (both view). It ranges from ~1.5hz to ~3hz. The video output of X and Y appears to be true to what the crt shows, but when it flickers it swaps X and Y or something (My scope here doesn't have a Z, tek 2230). I've swapped A1A2, A1A3, A1A4 (XYZ axis amplifiers for the CRT) to no avail. I've also swapped the three power supply boards, as well as all of A3. When I swapped the upper half of A3, the flicker rate changed. From my meager electronics repair experience, it seems like X and Y deflection voltages leak to zero every refresh, on both traces. In addition, the 118V unreg on both psu boards reads around 90V, and the 100V unreg reads 71V on both as well. Any ideas? I've swapped everything except the A1A3 HV regulator and the IF section. I've attached videos of the screen in test modes and at startup. How should I go about troubleshooting and repairing it? I have a square/sine signal generator, multimeter, DSO scope, and a universal counter.

If it wasn't the power supply, transformer, or anything downstream causing issues, that doesn't leave much. It was one of the three large filtering capacitors I replaced, that sit behind the crt.

[pnv57]

More troubleshooting: I tested the three PSU boards in my other 85662a display (nothing comes up on the CRT) and in that chassis the 100V rail light comes one, and the 100V and 118V unreg test points both show good voltage. I then looked upstream, and proceeded to swap the entire transformer assembly from the other one with no display but good power. No change whatsoever, meaning that the problem either lies in the motherboard (unlikely) or that the low psu voltage is an effect and not the cause.