Diagnosing Macintosh Classic

[SpocksBeer]

It does that much without UA5 being present? Interesting I would not have expected that.

The variation in screen brightness may be down to electrolyte that has seeped into the PCB of the analogue board. It's quite porous and a real pain to deal with. Usually a deep soaking clean is required if this is the case - hot soapy water, or a ultrasonic cleaner if you have one

 

[DJ68K]

It looks like the "Screen" adjustment is overdriving the flyback. I suggest you adjust the brightness/contrast dials on the analog board. The Service Manual (page 89) has instructions on how to do this; ignore the light meter stuff (unless you have one) and adjust it so the non-lit areas around the sides of the screen (glass, but no image being projected) is as dark as possible.