Well, D2 is toast. Shorted. I'm hoping that's all that's gone. The
transistors close by (TS1 & TS2) are all surface mount, so I'm not
planning on ripping them out just to test them. TS3 seems ok as LED1
still lights.

I'll get another zener diode in the morning, and keep my fingers
crossed.

Just out of interest - is there a quick way I can test TS1 & 2 whilst
still in-circuit ?

Cheers,

Kev.