Sega 32x passthrough works but 32 bit cards don't

I have a Sega 32x that I bought off ebay as not working. I have tried it in a Megadrive Genesis, with and without MegaCD and also in a Megadrive II with and without MegaCD. Passthrough (with Genesis games) works fine. I have three 32x Carts (Starwards, Virtua Racing and Doom) and none of these work. The Sega copyright screen appears but then nothing.

I have cleaned and tested continuity on all the connectors and also on the white ribbon cables. Everything seems fine.

Any advice?

Ok - so it appears to be related to cleanliness of the contacts. I cleaned them with contact cleaner but I think this has some detergent in it - I've now cleaned them with IPA and it's working fine.