Thanks Andy - It is an and I also looked at the circuit digram last night, but decided that the couple of glasses of red wine were not conducive to going further…
Today I looked inside and expected to find about 40 years worth of bodging. (I am assuming it was made in about 1985) and … it was perfect inside the box with no sign of anyone else opening the box at all in the last 40 years. Not only that but there was a clearly labelled circuit board with components big enough to see - even without glasses on! The capacitor was labelled, had nothing else in parallel and was even labelled 4.7 so…
.., a bit more investigation required… Was it the FT-817ND (which didn’t do it on FM) or is the capacitor just a bit too big?
Meanwhile I have got the Ukrainian transporter board back out to finish my plan B ( - which hopefully will be a bit lighter - and visible without glasses! ) Thanks Andy 73!