I have a problem with my newly acquired X68000. I recapped the machine completely (except the floppy drives), changed the power supply and got it running. However, the (VGA-) video output is corrupted. It usually starts like this:

(Noisy white vertical lines, static blue vertical lines)
After a while (or with some fiddling of the video-output board) it changes to this image:

(White noisy vertical lines on the left, static blue vertical lines)
Unfortunately I am no expert in electronics. I ordered an oscilloscope (but I don't have it yet - and I'm also not sure if my knowledge is enough to make any reasonable readings) and would appreciate any help diagnosing the cause of this fault.
What I found so far:
1.) The intensity of the white noise changes when changing the intensity of the green signal (there are three potentiometers for the three colors)
2.) The intensity of the blue lines changes when changing the intensity of the blue signal
3.) Changing the intensity of the red signal doesn't really change anything
When looking at the schematics of the mainboard:

The issue COULD be the video processor (IC50), the DAC (IC14), the VRAM or one of the transistors or resistors.
When looking at the schematics of the video output board:

The issue could be a transistor, resistor or one of the caps (which I replaced with 16V 470uF models instead of 10V 470uF). The issue could of course also be my amateurish designed VGA-Adapter which I realized through a custom PCB.
Could anybody help me with a more experienced perspective?
Thank you SO MUCH already!
[Edit/Update]
I just noticed that inbetween all the OKI M51C262-10 memory modules there is one slower single MN47464L-12 module, which seemed to be soldered in by hand. However, when I opened the X68000 everything seemed pretty much in its original condition. Only the PSU was defective due to leaking capacitors. Could this module be the problem - or could it be a VRAM problem in general? I don't want to perform a shot in the dark and order new parts which aren't the culprit.