If a SOUND statement is issued with a channel number greater than 2, the system hangs. For example:
SOUND 3,-15,10,100
will cause this issue.
Assume only 3 channels (0-2) supported. Note that BBC BASIC supports 3 channels (1-3) and a noise channel (0)

MOS: 1.03 RC1
VDP: 1.03 RC1
Basic: 1.04 RC1