[Mike Rivers]

Bluesbreaker wrote:

Well, I've cracked open the mixer. There are only a few ribbon
cables. All are soldered rather than being attached via a plug. I'm
not sure that DeOxit will help in this case.

If there are no connectors, it's been modified, probably by someone who
decided that was the ultimate solution to the ribbon cable problem. I don't
know what to tell you but it sounds like a shop job to me.