F7sus4
"U5 901225-01 CHARACTER ROM
Blank screen with border or screen full of shimmering lines or characters.
Partial failure: "garbage" characters or blocks where startup page info should
be. Cartridge works."
lub
"U9 318013-01 (8580) or 906112-01 (6581) SID (SOUND INTERFACE DEVICE)
Blank or "garbage" screen if shorted (remove to test), otherwise normal
screen. No sound or garbled sound. Mouse or graphics tablet pointer stuck or
jitters. NOTE: for test purposes, computer will work without a SID plugged in.
NOTE: 8580 and 6581 are pin compatible and somewhat interchangeable, but only
with board component changes: pin 28 supply voltage either +9 or +12VDC, and
two capacitors values must be changed for correct voicing."
W dużym skrócie. Sprawdź go z kartem na początek, lub bez SID'a.