Hi. Have you looked at the pin repair site for Baby Pac yet? It talks about this problem and says molex connectors are usually the issue.
www.pinrepair.com/bally/babypac.htm

The J1 connectors on the MPU and Vidiot are 28 pin wafer connectors and J2 on the MPU are 15 pin.

I would think Steve Young at the PBR might have those header pins, or Marco Specialties has connector rebuild kits that come with like J1, J2, etc pieces, or even Mouser electronics should have them.

The 28 pin .100 plug used is no longer manufactured by Molex. The one place I know that has stock of this plug is Ed at Great Plains. Once anyone who has it in stock runs out that will be the end of it.

Also to the OP one trick to try is while the communication test is running, press down gently on the U11 PIA on the MPU board and have someone observe the screen to see if the numbers on the monitor change in any way. If they do you probably have battery corrosion under the socket which will need to be mitigated.

viperrwk

http://www.taydaelectronics.com/connectors-sockets/wafer-housing-crimp-terminal/serie-2500-2-54mm/wafer-connector-2-54mm-14-pins.html

Use two. The friction lock tears off with diagnal cutting pliers.

What's the issue with the drops specifically?

viperrwk

The drop target with the captive ball behind it will always drop. Is the captive ball behind the left target? If the captive ball is behind the right target does the right one stay down?

The middle one is on a timer. each time you start pinball, hit the captive ball across, or hit a yellow drop target, the drop targets reset and the timer is reset. If you do not hit any drop targets or the captive ball before the timer runs out, the blue target in the middle will drop down on it's own. The timer gets shorter and shorter as you gain green arrows leading up to an extra baby. if you look closely on the playfield, each arrow says how long the timer lasts with that particular arrow lit.