Thanks for the info- I'll have to look in to it some more, since the little flip-switch cover is missing; there's no indication which tip is what.
(Time to take out the microscope and look at the tips... which would also show how worn they are!)
It seems the turntable is a BSR UA-14. Some googling reveals that:
a) these typically had TC8M cartridges, and
b) if that is the case, we have a crystal cartridge on our hands.
As such, it is very likely that the crystal is dead; I might well look in to replacing the cartridge with a magnetic one to save wear on the discs. (I know I'd need a preamp, re-balance the tone arm, yada yada yada...) Ugh, not something I want to think about now.
What's more, the TC8M appears to be MONO! This would make sense, since there are 4 leads running through the tone arm, but one of them is not connected to anything... seems the "stereo" in this set was nothing more than snake oil, unless the audio outputs share a common ground. Probably sold as "stereo capable" or some such, requiring an after-market upgrade.
Edit: Yup, crystal:
http://www.hupse.eu/radio/reproducers/TC8S.htm