Clay's method on pinballninja.com (membership required) of diagnosing problems with game resets ultimately caused by a voltage drop between the power driver board and the MPU board is very quick, precise, and methodical.

(He typically gives a reminder that replacing the bridge rectifier and capacitor is not a good first step.)

Before reseating any connectors, he measures 5V on the power driver board (test point TP2) and on the MPU board (positive bottom side of C31). Let's say we get 4.97 V on the driver board and 4.80 on the MPU board.

We already know that we don't have a bridge rectifier problem, as the voltage on the power driver board is respectable. We know that the voltage drop is occurring on the connection between the two boards. So we check out those connections one at a time.

Lift and reseat J114 on the power driver board, and measure both voltages again. TP2 will probably stay the same. Voltage on the MPU board may go up by a couple hundredths of a volt. Let's say we know have 4.97 V and 4.82 V. That means J114 was not perfect, but perhaps not the biggest culprit.

Now, lift and reseat J210. Measure again. If the voltage jumps up to nearly that on the power driver board, we just determined that this connector is the cause and we can fix the problem by replacing the female and male connector/pins.

If we still didn't increase the voltage much, reseat the Z connector and measure again. If this causes the voltage to increase significantly (which 0.1 V would definitely be significant), we will have identified that the Z connector is the problem. At that point, we will have definitely proven that it's problematic. Even though reseating it may temporarily fix the problem, the real solution in this case is removing the Z connector and permanently attaching the wires.