You can test the PSG sound channels with simple SOUND commands in BASIC:
SOUND 1,440,1000,15 should produce a 440Hz sound for 10s in the left speaker. (channel A) SOUND 2,440,1000,15 should produce a 440Hz sound for 10s in both speakers. (channel B) SOUND 4,440,1000,15 should produce a 440Hz sound for 10s in the right speaker. (channel C)
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