As paulace points out, if the P relay coil is dead shorted, then the rollover relays will still trip, but the P relay won't energize.
To check for this, you can try the following test with any of the rollover relays. Hold one of the rollover relays in the latched (reset) position with your hand. While still holding the relay, use an insulated tool to actuate the rollover switch on the PF that energizes the relay you are holding. The relay you are holding should buzz loudly, and the P relay should also pull in and stay on the entire time you are holding the rollover relay in the latched position AND holding the PF rollover switch closed. As soon as you let the rollover relay drop, or release the PF switch, both the rollover relay the P relay should de-energize.
If you can energize the P relay doing the above test, then I suspect the make-break switches on your rollover relays are adjusted to open very early as each relay trips. That would break the connection to the P relay so quickly that the P relay would not pulse long enough to energize the G relay. If that is the case, try adjusting the make-break switches on the rollover relays to open later, to see if that gets things working again.
If you can't energize the P relay by doing the above test, then the next thing is to determine why the P relay never pulls in. It could be a dead-shorted P relay coil, or there could be a wiring short between the rollover relay coil common wire and the transformer black wire. Such a short could either happen by accident, or because of a prior incorrect repair attempt on this part of the circuit.
One thing to remember is, if you can actuate a rollover switch on the playfield, and that does indeed trip the corresponding rollover relay, then in theory the P relay coil MUST be getting energized unless it is somehow shorted out or bypassed. That's because the P relay coil is part of the common return wiring for all of the rollover relay coils. (If this part of the circuit were open, then none of the rollover relays could trip.) This is why the P relay is called a series relay - it is wired in series with the rollover relays.
This also means, of course, that the P relay coil and all the rollover relays need to be 12-volt coils, rather than the usual 24-volt coils. So, it would probably be a good idea to check the P relay coil and confirm it is an R20-2 coil.
- TimMe