Macintosh Plus with Wide Vertical Bars

I’ve adopted a very sad-looking Mac Plus that was dumped in the corner of the workshop. Before even powering it on I gave it a surface-level clean of the analogue and logic boards because they were absolutely filthy.
On the first power on, there was no bong, I could see wide vertical bars that were only visible on the top half of the screen. There was a bright horizontal line in the middle of the monitor and I made sure now to run it for too long like this so I didn’t burn in any lines into the CRT.


I noticed that the screen would jitter if I banged the analogue board, so I decided to reflow all the solder joints to the main connectors. After this, the vertical bars filled the rest of the bottom half of the screen and the jittering was gone.


There’s still no bong, and according to various forums and the dead mac scrolls, the wide vertical bars is apparently caused by bad RAM or faulty ROMs. I cleaned the pins of all the RAM and ROM and reseated them the best I could, but there was no improvement.
Would anyone know of a way to troubleshoot this further? I don’t have any spare RAM or ROMs on hand to swap them out.

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You can run the plus with limited ram for testing. I’ve only ever seen one faulty ROM on a classic in all my years. Are the power rails OK?