Check the PF switches for the bottom right-side rollover on the return lane - it's the lane that feeds the ball back to the right flipper.

As Mopar has already posted, you'll also want to check the A and B rollover lane switches. These two PF rollovers are sometimes selected to energize the 300/3-ADV relay via a make-break switch on the alternator relay.

If all the above PF switches look good, there might be some kind of bad adjustment or short at the make-break switch blades of the alternator relay, such that the 300/3-ADV relay gets energized all the time. So it would probably be a good idea to check the switches on that relay and confirm all is well.

- TimMe

It's very difficult to use an ohm meter to check switches on an EM unless you disconnect each switch from the circuitry. When you measure across an open EM switch in-circuit, you can get a lot of weird and false readings. So that is one thing that has probably been confusing.

About 98% of the time, an electrically stuck scoring relay is due to a PF switch problem, and it also happens to be the easiest thing to check. That's why we techs keep going on about it. You don't need a meter to check PF switches, but you do need to examine each switch closely with a sharp eye and good lighting. Can you see a gap between the switch points? Have you confirmed that there are no backing blades crossing the switch blade gap and making contact? Have you confirmed that none of the solder lugs for the switch blades are bent over and touching? Have you confirmed there are no solder splashes across switch blades or on the phenolic switch stack, causing an electrical bridge? If you can say "yes" to all of these questions, then you can be very confident that switch is not the source of the fault.

Also, most rollover switch stacks have more than one set of switches on them. Have you confirmed that every set of switches on each switch stack pass the above tests?

If you are 100% sure it's not a stuck PF switch, then that means there is some unusual fault that is causing the relay to energize. This does indeed happen, and it is difficult to track down. One way this happens is when adjacent switches on a relay, for two completely different circuits, end up touching by accident. That is why I said to look at the alternator relay. Again, you just need a sharp eye and a good source of light to check this. You'll want to examine all of the switches on the alternator relay itself. The most common way you get a short across circuits in a relay is due to bent switch blades, solder tabs (for the switches) that are bent over and touching each other, and solder splashes across the switch blades or on the phenolic switch stack. You should be able to visually confirm whether any of those kinds of faults are present at the relay switches.

One other thing I just want to mention for completeness. On the Bally EMs of this era, relays sometimes stick electrically, and they sometimes stick mechanically (because they get slightly magnetized and/or get gunked up). From your original posting, it sounds like the 300/3-ADV relay is sticking electrically. For your own peace of mind, you can confirm this easily by turning off (or unplugging) the machine while the relay is stuck in the energized position. If the relay is sticking electrically, the relay will drop out immediately when you shut off the power. If it is sticking mechanically, it will stay pulled in even with the power off. You should be able to repeat this test several times, and never see the relay stay pulled in when you shut off the power. If you ever see the relay stay pulled in even once with the power off, you have a relay that is sticking mechanically.

Hope this helps. - TimMe

Some other things to try:

Make sure you do the test to confirm the relay isn't sticking mechanically, if you haven't done that already. You'll need to do the test several times. Relays that stick mechanically have fooled me a few times.

With the power off, unplug the playfield. Then, turn the machine back on and start a game. If the 300/3-ADV relay is still pulling in, you have a fault somewhere on the bottom board wiring. If the 300/3-ADV relay no longer pulls in, the fault is somewhere in the playfield wiring.

To get access to the back side switches on the alternator relay, remove the mounting screws and flip the relay up so you can get at the switches.

The 300/3-ADV relay problem will almost certainly NOT be because the alternator relay is off all the time. If the problem is at the alternator relay, it will almost certainly be because there is a short across two different circuits, energizing the 300/3-ADV relay. One thing you can try is to press in and hold the alternator relay, and see if the 300/3-ADV relay drops out. If it does drop out, then it is very likely that there is a fault with the switches on the alternator relay. On the other hand, if the 300/3-ADV relay stays pulled in, it really won't tell you much of anything.

Finally, while the alternator relay is a likely place to check for the fault, because the 300/3-ADV relay coil wiring goes through switches on that relay, the fault may be somewhere else.

- TimMe

The red wire that is common to one side of most coils under the PF is a common power supply wire. It is the coil power for "game on" and is a conditioned version of the black main power trunk line that is directly attached to the 50 volt secondary of the transformer. The red wire is basically the same as the black wire, but with the ability to be turned off by a reset relay switch, tilt relay switch, or game-over relay switch.

The main red wire is usually a large-gauge cloth-covered wire that is daisy-chained from one coil to the next, but sometimes a thin short jumper wire is used to connect the main daisy-chain over to a nearby neighbor coil. The jumper color may be non-red due to the intended wire color not being available at the factory on the day the machine was built. Factories did wire-color substitutions all the time to avoid halting the production line.

In any event, that jumper would not affect the alternator relay coil operation unless it was shorted out, in which case it would affect a lot of the coils.

- TimMe

In reading your post #10 again, one other thought comes to mind.

If you are saying that there is an orange wire jumpered across two coil lugs that both already have a red daisy-chain wire soldered to them, that is probably a wire that was added by someone in the field, as a repair. You will usually see this kind of repair when a portion of the original daisy-chain has a break somewhere, and someone has jumpered it as a way to restore the power to the coils downstream from the break.

This fix should be considered somewhat of a hack. Techs sometimes did this because it was faster than finding and correcting the break in the wiring. From my perspective, this is not the best way to make this type of repair. A better way to make the repair would be to locate and correct the actual break in the original red daisy-chain wiring.

Not sure if this is what is happening in your game, but it's one of those things that you see from time to time.

- TimMe

No need to be nervous, these kinds of hacks are common in vintage EM games.

If you want, you can remove the hack jumper and see what coils stop working on the PF. Then you can look for the break in the red daisy-chain wire, and fix it. The break is most likely at one of the coil solder lugs, which could be at any coil on the PF that uses the red wire for the power supply.

If all the coils continue to work, then you should just leave that hack jumper off the machine. On the other hand, if some coils do go dead, and you can't find the break in the red daisy-chain, you can always put a jumper wire back on your game, at the same place. Use a thicker gauge wire, and do a better job of soldering, and you'll be that much better off.

Note that if you focus on this problem, you'll be spending your time on a totally different problem than fixing your stuck 300/3-ADV relay issue. That's not a bad thing, it's just a personal decision. You may want to keep working on your stuck relay issue for now, and deal with the hack jumper later, when your current issue is resolved.

As for the alternator relay not working, if the coil is out of the circuit, you will not get an ohm reading across a coil if the coil is bad (open). A bad coil will either be open (infinite resistance) or dead shorted (1 ohm or less). HOWEVER, you can ONLY check the ohm reading across a coil by disconnecting one of the coil leads, and checking the coil out of circuit. If you check a coil in circuit, you are no longer assured that you are only measuring the resistance of the coil, and you can be fooled by seeing a reasonable resistance reading, even on a totally open coil.

If the alternator coil is good, but it now won't energize when the 00-90 switch is closed, try wiggling the jones plugs in the sockets, and maybe slightly pulling up and reseating the plugs, for the cables you removed when you unplugged the PF. Bally jones plugs of this era are notorious for having connection problems. Also make sure you got all the cables plugged solidly back in. Checking (and re-seating) the jones plugs for the cables plugged into the head wouldn't hurt either.

- TimMe