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