Interesting indeed.
If one clock (CLK1) is working and the other is not then you shouldstill hear one out of every two notes when in single mode. And when indouble mode you should hear just DCO1 (which gets its clock from CLK1)while DCO2 would be dead (getting its clock from CLK2).
If you don't hear any DCO's at all (holding down eight notes forexample) then check for write pules on MSM5232 pin 12. If there's nowrite pulse then check IC16 (40H32). You will most likely need a scopefor that although a logic probe with hold mode can do the tricksometimes. And check for the ALE signal on pin 13. If there's no ALEsignal then check IC27 (40H000).
If CLK2 is stuck at +5V then you will need to work you way back throughthe detune circuit (IC's 17 (40H074), 18 (40H000), 19 (40H151) and 20(40H393).
These form a modulated phase shifter (thus detune).
Mike.