There is a bank under the Playfield that controls the scoring. You should here a buzz sound when a rollover is activated. I would clean the contacts on that bank. It is usually held in place by 2 wing nuts .loosen the wing nuts and the bank should swing down giving you access to the leaf switches that need to be cleaned.

The rollovers all feed their corresponding 1B through 12B sequence relays (along with the standup targets in the mix). These 1B - 12B relays are then connected to the series relay, P.

When P activates, a switch closing there activates the E relay (500/5000pt relay) through a normally closed score motor switch at 1C.

E should then lock on via a switch closing of its own and a normally closed switch at score motor 2B.

P de-activates as soon as the rollover switch that activated it opens.

So it's important that E gets energized and locks on before missing the signal from P.

A switch closing on E causes the score motor to run, in conjunction with a normally closed switch on P. So this sets up a possibly touchy timing scenario; P needs to activate to activate E, E needs to lock on and catch the normally closed switch on P to start the score motor running.

While the score motor is running, another switch closed on E will cause either the 100pt or 1000pt relays to activate (M or L), depending on whether the game is set on Add a Ball or Novelty mode, via score motor switch at 1A (which pulses five times to get the 500 or 5000 score).

So... check the switches on P and E. Tighten the switch stacks, burnish the contacts, check the gaps.