That took a while. At least I was right about the area of the circuit that
there was a problem.

9V zener/reference diode? No
2u2 or 15u tant? No

Turned out to be C447, an 0.47uF 50V ceramic. This is in parallel
combination with the 2u2 tant and one of the 9V diodes. Reads 200 ohms on a
meter.

Found by removing U474 and looking at the voltage on each end of the 9V
diodes.

That has taken bloody hours. A 50V ceramic just did not seem like a
possible candidate.

Voltages all now are pretty much bang on. Phew.

Craig