Issue: No background music.
Fix: U42 (music control PIA) outputs test OK with Leon ROM but corrosion in area. Remove U41/42 PIAs, clean corrosion, and add sockets. No continuity from U42-16/17 to SRC3, fixed. Install new U41/42 PIAs. Remove U37 (LS138), clean corrosion, and add socket. Install new U37 chip.
