The phillips head screw isn't all that strange- I have a few Majesco-era carts with those in them.
Assuming you've cleaned the thing to make sure 'poor connection' doesn't mean the pins, I'd try taking it to any local retro shops/events you might have around, see if you can find someone with a link cable to try it with. It could also want you to connect it to a PC if it's a diagnostic cart- maybe look around for that previously mentioned service manual for more info.