Phil, I just got continuity to chassis for literally a second or two from the base of one of those diodes using the continuity tester on my multimeter, which admittedly is a cheap Maplin job that is probably 30 years old.

But then it just goes/disappears. Even after discharging the orange caps you can see in the pics.

I thought software was hard but I really am realising hardware can be an absolute bitch.

Sometimes, you just need to hire someone who has been in the field for a few decades and pay for what they know.

At least, that's the conclusion I am coming to for this case.

These things are worth saving because they quite literally are outstanding examples of their ilk for the time period.

Like the best classic cars.