Just a quick update on this.

I think I got it working again. Voltages are stable from turn on and machine boots straight away. Need to check temperatures and compare them to my other Classic but so far, so good.

All I did was resolder the QP2 MosFet and replaced a dodgy looking 1uF cap (which I had already replaced).

Regarding 120-240V conversion, here's what Larry Pina says (also as Ike says):

For 110VAC, jumper JP1 must be installed.

For 220VAC, jumper JP1 must be removed.

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