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Gottlieb 1972 Gottlieb Grand Slam Reel Reset and 1 weak pop bumper

teamhex

I PwN nOoBs
I signed up on here ages ago when I was in my late teens. I've had this machine for quite awhile now and I decided I should start trying to fix some of the issues.

I recently replaced all the rubbers, bulbs, and plunger springs so it plays a lot better.

It plays, but It would be nice to have an accurate score for each game played. Instead it just resets to 0 and counts up if you get over 99,999.

On a rare occasion the score/runs will reset when you "insert" a coin, but I found a way to reset the score reels by tapping this relay then putting a coin in.
Could someone tell me where to look to make the score reset reliable? I'm guessing this is a dirty contact type situation since it does occasionally work....we're talking...once every 40 games or so.

Here's a video of me showing the relay and the process I use to reset the reels. Also here's some pictures of that relay.


Also my left pop bumper doesn't seem to launch the ball at all. It does pop when hit, but doesn't kick the ball back like the right one does. I assume this is an adjustment issue, but I could be wrong.
 

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Ike Savage

Froggy like robot
Staff member
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Hmm. The schematics don't seem easy to find anymore, I guess because Gottlieb pulled most of their resources online.

There's a guy who stops by regularly who can probably sort this out, but meanwhile you might want to start looking at PinRepair.com.
 

teamhex

I PwN nOoBs
I think I have the originals in a tube and some reproduction ones in a manila envelope. The issue is reading them. Funny enough I'm a computer technician, but I don't go down to the circuit level of things. If a part is bad we just replace it.
 

Ike Savage

Froggy like robot
Staff member
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I think I have the originals in a tube and some reproduction ones in a manila envelope. The issue is reading them. Funny enough I'm a computer technician, but I don't go down to the circuit level of things. If a part is bad we just replace it.
Hah, yeah... I also used to be a PC tech guy (long time ago, now) and never really learned the circuit side past the beginner level. For me, the main use of a schematic in these EM's is to trace back to some likely relays, clean them up and cross my fingers. I used to use white eraser pencils and occasionally other stuff to clean the leaf switches back when I had some EM's. Hopefully you've got some supplies like that around there.

If Dave sees this I'm sure he'll have some ideas. But that PinRepair site will probably give you some good ideas about where the troubles might lie so at least you can get started.
 

pinballdaveh

Pinball Technician
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Hah, yeah... I also used to be a PC tech guy (long time ago, now) and never really learned the circuit side past the beginner level. For me, the main use of a schematic in these EM's is to trace back to some likely relays, clean them up and cross my fingers. I used to use white eraser pencils and occasionally other stuff to clean the leaf switches back when I had some EM's. Hopefully you've got some supplies like that around there.

If Dave sees this I'm sure he'll have some ideas. But that PinRepair site will probably give you some good ideas about where the troubles might lie so at least you can get started.
All gottlieb EM machines use relays to control pop bumper operation.
Sometimes the pop bumper cap color is what the pop bumper relay will be called.
Sometimes a pop bumper relay will operate 2 pop bumpers at the same time.
Normally open switches with larger points are used to drive the pop bumper coils on the pop bumper relay.
Taking apart the pop bumper to clean the coil sleeve and plunger is helpful.
The video shows you tricking the machine into thinking that the reset sequence has been completed by flicking that coil plate.
It looks like there’s issues with the reset circuits that needs fixing.
Familiarize yourself with gottlieb reset sequence thru online videos.
 

teamhex

I PwN nOoBs
All gottlieb EM machines use relays to control pop bumper operation.
Sometimes the pop bumper cap color is what the pop bumper relay will be called.
Sometimes a pop bumper relay will operate 2 pop bumpers at the same time.
Normally open switches with larger points are used to drive the pop bumper coils on the pop bumper relay.
Taking apart the pop bumper to clean the coil sleeve and plunger is helpful.
The video shows you tricking the machine into thinking that the reset sequence has been completed by flicking that coil plate.
It looks like there’s issues with the reset circuits that needs fixing.
Familiarize yourself with gottlieb reset sequence thru online videos.
Excellent. I'll bust out the paperwork here and see if I can figure out that restart sequence.
I assume the scores are supposed to reset at the beginning of the game based on past experience of it working.

I'm just curious why the reset complete relay...resets the reels. Seems odd to me. So I know the reels work for sure since they do reset when I do that. I guess I should be looking at what ever sends a signal to that reset complete relay coil and start there.

The pop bumpers seem to work, but only the right one launches the ball with enough force to actually send it away from the bumper. The left one just pops, but doesn't launch it. I'll start by taking it apart. I did read that if it activates, but doesn't launch the ball the issue is most likely a switch that needs to be adjusted. Something about it being activated with a light touch. Maybe it's travel is too far so it doesn't activate in time? No idea, but I'll with that I guess.
 
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teamhex

I PwN nOoBs
Upon inspection I figured out why the left pop bumper isn't launching the ball...though I'm not sure what I can do to fix it other than buying a new rod assembly with the nuts.

The rods aren't connected to the plate on the coil. The pop bumper on the right has threaded ends with some small nuts on it.
I'm starting to think someone put on a rod assembly from another machine or something. I don't even see threads on these.

If anyone knows a site that sells them and knows what part it is. Please link me. I'm going to take both apart and polish up both of them before putting them back together.
 

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pinballdaveh

Pinball Technician
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Upon inspection I figured out why the left pop bumper isn't launching the ball...though I'm not sure what I can do to fix it other than buying a new rod assembly with the nuts.

The rods aren't connected to the plate on the coil. The pop bumper on the right has threaded ends with some small nuts on it.
I'm starting to think someone put on a rod assembly from another machine or something. I don't even see threads on these.

If anyone knows a site that sells them and knows what part it is. Please link me. I'm going to take both apart and polish up both of them before putting them back together.
Pinball resource for gottlieb.
Marco specialties has a good online order site.
I thought someone posted about all the parts sites awhile ago.
 

teamhex

I PwN nOoBs
Pinball resource for gottlieb.
Marco specialties has a good online order site.
I thought someone posted about all the parts sites awhile ago.
I'm new to this forum so to speak. I signed up a long time ago, but haven't had time to browse.


Alright so I talked to their support and mine doesn't use that longer style one. Got the new parts ordered. Guy was super helpful and recommended some other parts that should be replaced when you rebuild these. All set on that.

Thanks for all the help gents.
 
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teamhex

I PwN nOoBs
I rebuilt the pops/flippers this weekend and installed LEDs (don't worry, I went warm white for the original look).
The game plays a lot better now after a rebuild and adjustment to the EOS switches. Can't believe I put it off that long. It wasn't that expensive and took about 5 hours(first time soldering and rebuilding these things). One of the flippers had a metal sleeve in it! Just crazy, and it explains why the flippers were so weak.

Video if it playing after the rebuild.


Still chasing down that reset relay thing though. I did find some great information on that Pinrepair link, and the guy even mentions the Grand Slam in this section, but based on this I should check the start relay first. Something isn't consistently triggering it. The crazy thing is, I got it to work for 9/10 times for about 30 games. It was exciting...then it quit working again haha.
  • A switch on the start relay and score motor pulls in the V reset relay (an interlock relay). A switch on the V relay causes the start relay to de-energize (the start relay was energized for just an instant while all the previous steps occur).
  • A switch on the V relay and the score motor (which is still turning) causes the score reels to reset to zero.
  • As soon as the score reels reset to zero (closing all the score reels zero position switches), the Vr relay pulls in. This releases the V relay (the V relay was locked on for a few seconds as the score reels reset to zero).

The relay that triggers it is the V relay called "Score reset complete". If I touch the metal tab it hits the switch stack and resets the scores, but keeps running until you coin in. That leads me to believe the switches are just fine on that stack. Maybe I could desolder and check the resistance on the two coils of that stack.
I may have the schematics in a "tube" somewhere so I'm going to check that first. If not, I'll likely have to buy a replacement set(unless someone has an online option where I can view them).
 
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Ike Savage

Froggy like robot
Staff member
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Wow, if those flipper coils are original spec, I might just have underestimated how strong flippers from the era were, when new.

Makes me miss the good ol' days of working on my 70's EM's. :s
 

teamhex

I PwN nOoBs
Wow, if those flipper coils are original spec, I might just have underestimated how strong flippers from the era were, when new.

Makes me miss the good ol' days of working on my 70's EM's. :s
Even before the rebuild, I adjusted the EOS on both flippers. Also cleaned it and the flipper button switch. That gave one flipper a good 20% boost in power. I always just thought EMs had weak flippers. They come pretty close to my Williams Firepower now. Not quite there, but approaching it.
The pin has over 85,000 plays on it and I'm surprised it's held up this well. I think someone must have rebuilt at some point because the coil stops weren't bashed in or mushroomed. I actually reused them because of how good they looked. I was really surprised when I took them apart.

I think the flippers had to be pretty strong on this one. You have to really hit those roto targets in the back. Even with fast flippers it's hard to trigger them. I heard you have to mod them to get them to register properly. I'm not sure if that's from wear and tear, or if they were like that from factory(probably wear and tear). I know they work if I manually hit them, but they have to travel like 1.5" just to make contact.

Hopefully I can get away with just cleaning the switches on the S and V relay again. Cleaning the switches on the V relay and adjusting the metal on the latch relay seemed to get it working last time. Ohh well, I'll just have to put more time into it.
 

teamhex

I PwN nOoBs
S relay is fine. Definitely the V relay causing this issue. I think it’s either a weak/bad coil, or the metal pieces aren’t adjusted right.
Here’s a video of me messing with it.

 

teamhex

I PwN nOoBs
Now that I look at it. In that one part of the video it looks like it's hanging up on the edge of the metal. Maybe filing it and doing a polish would help them slide around much better. Still going to check the coil on the right. I feel like if it was strong enough it wouldn't matter.
 

pinballdaveh

Pinball Technician
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Now that I look at it. In that one part of the video it looks like it's hanging up on the edge of the metal. Maybe filing it and doing a polish would help them slide around much better. Still going to check the coil on the right. I feel like if it was strong enough it wouldn't matter.
The spot where the 2 plates slide against each other only needs to be clean, no need for polish.
In the video the latching coil is struggling to latch.
the switch stack long blades might be applying too much push against the pull in of the coil. Adjustment of the long blades and switches to lessen the push against the coil, helping the coil to latch properly might solve the problem.
 

teamhex

I PwN nOoBs
The spot where the 2 plates slide against each other only needs to be clean, no need for polish.
In the video the latching coil is struggling to latch.
the switch stack long blades might be applying too much push against the pull in of the coil. Adjustment of the long blades and switches to lessen the push against the coil, helping the coil to latch properly might solve the problem.
Should I loosen the switch stack and maybe gap it a tad more or just bend the long blade switches?
I suppose I could always buy and build a replacement switch stack.

So it’s unlikely that the coil is bad right?
There’s no plunger or movement so I assume wear and tear isn’t really a thing.
I guess I’ll just start tinkering and adjusting to see if I can get it. I feel like there may be some burrs on the edge of the flat metal pieces.
 

pinballdaveh

Pinball Technician
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Should I loosen the switch stack and maybe gap it a tad more or just bend the long blade switches?
I suppose I could always buy and build a replacement switch stack.

So it’s unlikely that the coil is bad right?
There’s no plunger or movement so I assume wear and tear isn’t really a thing.
I guess I’ll just start tinkering and adjusting to see if I can get it. I feel like there may be some burrs on the edge of the flat metal pieces.
These interlock relays are some of the hardest relays to adjust to get just right.
Luckily yours is the larger type that’s easier to adjust than the later gottlieb machines that have a smaller interlock relay which is harder to adjust.
 

teamhex

I PwN nOoBs
I used 600 grit sandpaper last night on the metal piece and it seemed to help for a few games. Then it kicked off again and hung up trying to reset the scores in the middle of gameplay. I think it also turns the score relay when this happens. I just turned it off since I didn't have the time. I'm going to look at it again when I get off work. Hopefully it's in the same position it was so I can see where it's hanging up. I should probably sand the outer parts that touch and see if it starts acting right. I still feel like maybe that one coil may not be doing it's job. I can see the one coil working and moving the switch stack, but the other one...I never see it move. If I tinker with it and that doesn't work, I may check the coil's resistance. I believe it should be 15 Ohms for that model coil. What would the resistance of a bad or weak coil?
 
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pinballdaveh

Pinball Technician
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I used 600 grit sandpaper last night on the metal piece and it seemed to help for a few games. Then it kicked off again and hung up trying to reset the scores in the middle of gameplay. I think it also turns the score relay when this happens. I'm just turned it off since I didn't have the time. I'm going to look at it again when I get off work. Hopefully it's in the same position it was so I can see where it's hanging up. I should probably sand the outer parts that touch and see if it starts acting right. I still feel like maybe that one coil may not be doing it's job. I can see the one coil working and moving the switch stack, but the other one...I never see it move. If I tinker with it and that doesn't work, I may check the coil's resistance. I believe it should be 15 Ohms for that model coil. What would the resistance of a bad or weak coil?
A bad coils resistance would be infinite resistance for an open coil, zero resistance for a shorted coil, and a higher than normal resistance for a weak coil.
Have you found the schematic yet to post some of the reset circuits?
 

teamhex

I PwN nOoBs
I only had 30 minutes to play it with last night, so I didn't get around to looking for the schematics.
The machine is in a room near my sons room and EMs have no volume control :)
I should have some time when I get off work today so I'll check for the schematics and try sanding the edges of those blades. It looks like that's where it's hanging up. Maybe making them smooth will allow them to properly move around each other.

Ok that's good to know. I assume I'll have to desolder the leads to properly test it.
 

pinballdaveh

Pinball Technician
Staff member
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I only had 30 minutes to play it with last night, so I didn't get around to looking for the schematics.
The machine is in a room near my sons room and EMs have no volume control :)
I should have some time when I get off work today so I'll check for the schematics and try sanding the edges of those blades. It looks like that's where it's hanging up. Maybe making them smooth will allow them to properly move around each other.

Ok that's good to know. I assume I'll have to desolder the leads to properly test it.
Unsolder the non black wire on each coil.
Test and compare resistance readings.
If consistent latching doesn’t happen, the trip coil frame mounting holes will allow for adjustment when screws are loosened.
this is usually a last resort and not meant to be adjusted, unless it was fooled around with before you got the machine.
 

teamhex

I PwN nOoBs
Someone fooled with it for sure. There’s a wire that goes from the coin door to the non black wire on this coil...or did go there. It’s unhooked, but I see a piece of copper stranded wire in the solder there. I have 3 black wires on one side of the coil, one goes to the other one. I’ll try desoldering and testing, but are you sure I don’t have to remove the black wire as well? I assume the test would be between two points so you’re probably right. Im also thinking maybe there’s a reset relay in the back box that isn’t doing what it should. Scores reset when I press that tab, but I notice the “runs” score reels hang. I also don’t think it’s calculating runs properly. Scoring seems fine though. If it’s not the coil, I think Im going to find the schematic and see what relay sends that reset signal to that V relay coil to latch or unlatch.
Thanks for the help gents. First time really digging into these machines. Not hard, but man it’s time consuming to chase down these issues. Im worried more problems will crop up if I tinker or fix one thing.
 

teamhex

I PwN nOoBs
Ok just tested it. 15 Ohms on it so it’s good. Now to track down the schematics and find out which relay it goes to in the back box. Im betting the issue could be that the runs don’t always reset fully which prevents the signal from reaching that coil.
 

teamhex

I PwN nOoBs
Alright so I got it put back together. Played a few games and it seemed ok, but now it likes to fire off that reset randomly during gameplay. I will look for the schematics since at this point I don’t think it’s that V relay. It has to be where it tells that V relay to move the way that makes it disengage.
 
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