EADGBE wrote:

Thanks for the link - I have already downloaded the service manual.
That's how I know the voltages for the secondary outputs.

I should have made that more clear in my original post (sorry).

The 3.5V you've lost is almost certainly the filament supply for the vacuum
fluourescent display. That explains why it's gone out.

Where does the other 3.5V go to ?

Graham