In reply to:

I've just realised my mistake- I've put the CA3140 in the wrong way round.



Aha! An Anti-Notchist!

We in the Pro-Notchist camp feel it is a basic ruile of tuner kit design that all the chips face the same way!

With a little luck, you may have gotten away with it. Carefully desolder and remove the chip, and put it back the way nature intended.

pca
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Experience is what you get just after it would have helped...