4-slot doesn't read carts

I wired my Neo Candy with a stereo/mono switch and it was working great for a while. Not sure if it has anything to do with it not working properly anymore (but I probably short something).

Well, now when I power on the 4-slot, it goes directly to the cross hatch test. Is there a simple fix, even if it requires desoldering?

THanks in advance.

First thing to do is clean the cart connections and mother board slots.
http://www.hardmvs.com/html/slotCleaning.htm

Yes, the slot cleaning I did.
I just find it odd that all four slots simultaneously stopped working and act as if no cartridge is inserted in any slot.

The boards are properly bolted together with the included screw/bolt fastener at each lower and upper board interface.

I think I may have shorted/fried something because I remember pushing against the ground pins towards the +5 pins, and that's when to the cross hatch test.
I don't recall feeling a spark or shock though, so maybe that was all coincidence.

Ive had occassion when all the slots on my MVH6s behave like this, splitting the two boards, cleaning the slots put everything back together and it works. Is the 5 volts OK, if low it usually shows green back ground with some gfx garbage- not xhatch- worth checking anyway.