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I have 250407 Rev A.. gives me black screen or Screen full of garbage when Cartridge inserted.
Checked +5 and +12V and seem Ok (red light comes on)
Also checked the following U4 Kernal, U1 CIA,U7 MPU,U17 PLA,U19 VIC=ALL OK in working moterboard
Put Diagnostic 781220 Test..gives one blink so checked U12 Ram=OK
Also Checked U8 7406,U25/U14 74ls257,U15 75ls139,U27 74ls08,U14 74ls258=all OK
No small Logic MOS chips on this board which puzzles me why still not working
attached pics
Ha
Looks like the boot screen of my c128 
But serius:
Did u checked the blue caps ? The look a bit bendy
I would check all caps in general... and the connetions and wires that go to the cartrige port... maybe a up or downpull brige is gone
Boot screen is Black... Garbage Characters screen is with Cartridge
also just checked U20 556 imer=OK and U26 74ls373=OK
Check again U17 PLA.
checked PLA probobly 3 times..OK
si again its Black Screen on Boot and Garbage characters all over screen when Cartridge inserted(Kickman,Jupiter Lander)
Connect a floppy drive. Does it reset on power up of the C64? Had something similar not long ago. Started replacing the TTLs until I got the faulty one 
