Besides what you have already mentioned as possible causes, could be one, or more of the following:

1. Worn or dirty coil sleeve.
2. Worn coil stop. Could be magnetized holding the plunger acivated and keeping the coil energized.
3. Worn or gummed up plunger. The ends get mushroomed after years of use and could be getting stuck in the sleeve.

Easy to take apart for cleaning and inspection. Replace any parts that are worn.

Won't be any of that if the coil is staying energized causing the coil to buzz and get hot. Sounds like a set of contacts is stuck closed or from probably another coil locked on. To the OP, look at the schematics and determine all the switches and relays that would activate the bell coil. Work backwards and check the switches and relays.

If the bell is locked on electrically, check your F (Run) relay. There is switch on the F relay that closes when the relay is energized, and that switch is what supplies power to the bell coil.

It could be that the F relay is getting stuck in the energized position. If that is what is happening, it is most likely an issue with the ones-digit score unit for runs. There is a switch on the ones score unit for runs that opens when the score unit plunger is pulled in, and that releases the F relay. So either that switch is never opening, or the ones unit for runs is not getting energized.

If the ones unit for runs is not getting energized, that is due to a (different) switch on the F relay, which is supposed to close when the the relay is energized to supply power to the drive coil on the ones unit for runs.

So, it would probably be a good idea to clean and adjust the switches on the F relay to ensure they are making good contact when the relay is energized. Be sure to tighten down the switch stack screws on the relay before making adjustments. Both the bell switch and the ones unit switch on the F relay will have large contact points.

- TimMe

We're not supposed to post PDFs of full Gottlieb schematics because the copyright owner has told Pinside not to do that. You can purchase an actual paper schematic from The Pinball Resource.

We can post snippets of specific circuits, I will try to get one posted here shortly.

As for the blowing fuse issue, you may have a toasted drive coil on your ones unit for runs, have you checked that?

- TimMe

Here's the F relay circuit (you'll need to expand the pic to see it clearly).

The F relay is energized through a motor 1A switch when the hit unit is scanning to see if there is a man on a specific base. Once the F relay is energized, it locks itself on via the normally-closed EOS switch on the ones unit for runs. That EOS switch needs to open to allow the F relay to drop out. The EOS switch is on the ones unit for runs to ensure that, once the F relay energizes, it stays locked on long enough for the ones unit to fully index and step up the run score.

If the EOS switch doesn't open for any reason, the F relay will stay locked on forever.

GS_F_relay (resized).jpg

If you mean the drive coil for the ones score unit, you COULD unsolder the wiring from one side of the coil to isolate it from the circuitry, then test it with an ohm meter. If it reads 2 ohms or less, it's toasted.

However, usually all you need to do is visually inspect the coil. If the coil has fried, then the coil wrapper will be burnt black, the plastic bobbin and/or coil sleeve will likely show signs of melting, there will probably be soot on the metal frame around the coil, and it will smell like it has burned up.

You can compare the suspect coil to a coil on a different score unit to see what a non-burned coil looks like.

- TimMe

There is a reset completed relay on this machine (V) that is a latch-trip relay.

When the V relay latches (the armature is pulled against the coil) the machine is in reset and the score motor will run. When all the score units get back to zero, and the ball count unit is also at zero, the trip coil on the V relay will fire (through a motor 2B switch) to release the V relay armature and complete the reset.

So you should see if your V relay is stuck in the latched position. If it is, check all your score units. Since you have been examining the score units, the runout switches on one or more score units may have been knocked out of adjustment. Either a score unit is not going back to zero, or one of the runout switches on the score unit that needs to close at zero is not making good contact. That would prevent the game from coming out of reset.

- TimMe

Great to hear that you are making progress, and you did some good detective work there.

I strongly recommend that you order a schematic for your game from The Pinball Resource, if you have not done so already.

The N.O. switch at motor 4C pulses the ball return kicker coil (AKA the outhole kicker) to deliver the ball the to the shooter runway. So if that switch was never closing, the ball would be stuck in the outhole, the O relay would stay on, and the game would just sit there with the motor running. It sounds like that is what was keeping your game stuck.

Technically speaking, you weren't stuck in reset. We can assume the V relay did release properly at the end of reset, since the ball kicked out when you adjusted the motor 4C switch, and that wouldn't happen if the V relay was stuck on. But, the motor 4C switch never closing caused your game to act like it was stuck in reset. This is a good example of the kind of things that can make it challenging to diagnose EM problems.

If the triple relay (I relay) was out of position such that it could not actuate properly, then it would cause problems during game play, but it is very unlikely it would cause trouble during game reset.

The roto unit wheel must be lined up properly for the roto targets to score. That's because there is a rivet disc on the unit, with wiper fingers on the wheel, that determine what each roto target switch should score based on the position of the wheel. If the wheel doesn't stop in the correct position, the wipers will not be touching any rivets, and that will make the roto target switches go dead as they won't be connected to anything. So you'll probably need to clean and adjust your roto unit so that the wheel stops in the correct position. The roto unit on Grand Slam is rather fussy so it can be difficult to get the wheel to stop in the correct position 100% of the time.

For the ball count unit, it sounds like the wiper is adjusted off-by-one so that it is not landing on the correct rivet. When the ball count unit is fully reset, the single wiper connected to the frame of the unit (the one that lights the ball-in-play lamps) should be at the zero position - that is, one step BEFORE the rivet that lights the number 1 ball-in-play light. In other words, if you manually reset the ball count unit, and then step it up exactly one time, the single wiper should land on the rivet that lights the number 1 ball-in-play light. So you'll want to check the wiper and adjust it if it is not in the correct position.

When checking the ball count unit, it's a good idea to first confirm that the two set screws for the spider are really tight. The spider is that little three-armed thingy that that wiper is attached to. The set screws for the spider can come loose, causing the spider to shift around on the drive gear shaft. If the set screws on the spider are loose, it will be impossible to reliably get the wipers into adjustment.

By the way, the exact same issue can occur on the roto unit, with the spider that holds the wheel. So you'll want to check the set screws for that spider as well, when adjusting the wheel on your roto unit.

- TimMe

On the gear side of the ball count unit, there is a post on the gear that actuates two different switches. One switch is pushed open at the zero position. The other switch is pushed open at the 6th position. When either of these switches are open, the power to the playfield is shut off. It sounds like your ball count unit is pushing on the 6th position switch and opening it at the 5th ball position. If so, you need to adjust the 6th position switch.

It's good that you re-attached the jumper wire on the dual wiper set of the ball count unit, as that jumper is needed to step the ball count unit up after the 5th ball drains, to put the machine into the game-over state. On the single wiper (the one for the ball-in-play lamps) there also needs to be a jumper wire connecting that wiper to the solder lug on one of the three wiper adjustment screws. If this jumper is missing or detached, the ball-in-play lamps will go out intermittently.

To get the base advance working properly, check to see if the men-on-base interlock relays are sticking. Also, you may need to rebuild your hit unit stepper, or deal with cut rivets on the hit unit disc, which will cause problems. I suggest you search for postings on this topic in the Pinside EM tech forum, as there have already been threads devoted to this particular problem.

- TimMe