I tried replacing the fried ZD3 15 V zener with 3 5.1V zeners in
series. Result - zener smoke. Noticed afterwards that the PC land
connecting one end of the zener to a choke was "open". I don't
know if it was open immediately after the zener was replaced, or
whether this would have caused the zener failure.

Anyone know how I could obtain a schematic for this power supply
(Raite AV715)?

Bob