Diagnose and repair broken Mega Drive 32X?

I was sitting on this loose 32X in unknown condition for a few years, getting the essential parts for it over time. Now having 1) another MD2 PSU and 2) that AV bridge cable thingy, I could finally (try to) give it a shot.

With everything hooked up as it's supposed to be - 32X into MD2, game into 32X, bridge cable from MD2 to 32X, AV cable from 32X to TV, one PSU plugged into each - I get the "Produced by or under license etc." screen, after which it goes black. Resetting doesn't do anything; switching off and on again brings me back to the license screen and the black screen afterwards. Mega Drive (ex. Sonic 2) or 32X (ex. Star Wars Arcade) game makes no difference, both kinds do not work.

Opened the 32X up, can't see any obvious damage, it's free of dirt, etc. Reseated the flat cables going between the two boards, no change. Leaving one of them out and turning the system on prevents the license screen from showing up, so I assume the cables are okay. With a Mega CD connected, the MCD intro comes up when no cartridge is inserted, the whole thing blackscreens when one is.

So, as far as I can make it out, the MD is able to detect cartridges (license screen coming up) but the 32X is not capable of starting up correctly. Does the MD passthrough functionality depend on actual 32X/SH2-side activity - as in, the 32X says "oh, a Mega Drive game, gotta hand control back to the MD"?

In general, does anyone know of some repair guides that go more in-depth than just those flat cables, or know ex. where/what kind of fuse the system has? Would be great to get this thing going again.

 

Clean the absolute heck out of the cart slot in both 32x and main console, don't forget the cart end of the 32x. I have seen similar and a good clean fixed it.