OK, replacing the 510R with a 1k, I now get 15.1v at the zener, 15.8 at the base, and 15.2 at the emitter.
Anyone would think you guys knew what you were talking about, it's uncanny! ;-)
And now, a new riddle has presented itself.
If you look at the lower right of the schematic, above the power-mute circuit, you'll see a circuit comprising a 1458 dual op-amp, with a pot labelled "Mod Rate". This is the separate dedicated LFO for the Envelope circuit (It works like this: you pick a note and the phase changes with the envelope, as the input amplitude drops from the initial attack, the LFO CV becomes dominant over the Envelope CV and you hear the oscillation, very nice effect).
Anyway, when I first turn it on, this LFO refuses to oscillate!
I tried bridging the cap with similar values, I replaced the op-amp, no avail. Then I accidentally briefly turned up the signal from the function generator, and the thing sprang to life!
I have been able to reproduce this behaviour each time. I haven't tried it with normal guitar signals yet.
You'll notice, and this has me scratching my head also, the power supply for that particular op-amp comes off a voltage divider made from a 330R and a 2k7, giving it a supply voltage of around 13 volts. Why would they do this? It's a bog standard dual op-amp, not a great deal different from the 4458s they use elsewhere on the board which are running off the 15 volt line.