Did you turn pp1 and check the voltage when turning?
Okay, so I have the following results:5V should be 4.85 to 5.15. 12V can be up to 12.8 V. Look at both when turning and measure again after a few minutes!
Sometimes it is useful to turn pp1 from one end to the other before you turn on the classic.
What are the symptoms with it set to 1/3 clockwise? Is the picture stable?
If the picture is stable and displaying garbage on the screen, I'd refocus your attention to the logic board. If the picture is unstable, there is a problem with the AB.
Those white safety/line filter caps are probably OK, and even if they weren't they wouldn't be causing this.
If you leave it on for a while (a few minutes), does the oscillation get worse or better or the same?
Leaving it on for 5-10 minutes, the oscillation stays the same. At the final value I turned PP1 to, 12v stays at 12.74 and 5v climbs from 4.80 to 4.85 and stays there. No difference to the picture.
Those white safety/line filter caps are probably OK, and even if they weren't they wouldn't be causing this.
I would have agreed with this until last year when my Classic started showing a wavy image on the screen...
Not enough on the 5 volt range, probably a bad diode somewhere or a current leak, try reflowing around (can help)12v currently produces ~ 4.45-4.5,
If your Classic II LB is battery bombed I would remove the SMD caps, wash it in the dishwasher, and recap it.Thanks @bibilit , @CircuitBored .
I have ordered brand new filter caps - PME295 pcb mount cap,4.7nF 440Vac . Will see how this goes. Is there a particular orientation for installing them?
@bibilit , much appreciated, toning down to under 12v currently produces ~ 4.45-4.5, will re-test after installing filter caps.
I will also try recapping the LB with downrated tantalums (currently it has identically rated recap).
Have a couple of other Mac Classics awaiting work in the hope of making one from many, however the other AB is not responding (awaiting resistors, as earlier in the topic) and the Classic 2 LB I have is battery bombed & appears way beyond hope. Was hoping to ask the community one-by-one, however even repairing one is proving to be a challenge! Thanks for your help
Okay, so, filter caps replaced. Now it boots instantly without "jump-starting" ("tak-tak-tak-tak-boot").
Also carefully reflowed every single solder connection on the board @bibilit
However, the wobbly screen still exists, and now these black lines come. No matter how much I turn PP1, can't get over ~4.40v without exceeding +12v.
Should I remove & clean PP1 again? Really stumped here. Thanks all
Did you change the TDA4605?