It should also be noted, just trying this here, even with the cable connected, the SBC behaves like this, regardless of JP4's position. In fact, the chip is stuck like this until I connect from to the loader, and then when I disconnect it works fine. Once I disconnect from the loader with the serial port cable, and detach the cable, the program still runs fine, and even if I hit the reset button left and right, it still executes the program correctly.

I pulled the 430 and Im getting the same thing, with one exception. A program I wrote on the 430 does not work on the 420 now, the indicator LED flashes with what appears to be randomness.

The 420 is now in the board, and it still runs SBC monitor fine when the cable is connected.

Measured voltages with no serial cable attached :
Using CAP mode, not sup chip
Rset (pin 9) - 0.0403; when reset button is pushed, 4.956

EA and psen - 5 volt

With cable connected, but port not opened :
same.

Opening port (same, but then connecting loader :
EA,PSEN - 0.2 volt
RSET - 3.5846