(Topic ID: 201798)

Tech: GTB Sky Jump drop target teardown & rebuild


By spinal

2 years ago



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  • 94 posts
  • 13 Pinsiders participating
  • Latest reply 2 years ago by spinal
  • Topic is favorited by 4 Pinsiders

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There are 94 posts in this topic. You are on page 1 of 2.
#1 2 years ago

My Sky Jump drop target assembly was dirty and sluggish so I decided to do a complete teardown and rebuild as a learning exercise and will post details here.

I'm enjoying the journey of learning more about these great EMs so comments/answers/suggestions welcome - thanks

Let's get started...

The Sky Jump drop target assembly can be found on page 15 of the Gottlieb parts catalog 1978 available from pbresource.

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On page 16 & 17 are different drop target assemblies for later games that are used on games from Far Out (12-74) onwards which means the Sky Jump target assembly detailed in this thread should be the same as for:

Jack in the Box/Jumping Jack
High Hand
Hot Shot/Big Shot
King Pin
Big Indian/Big Brave
Sky Jump

Keep in mind though that later '70s Gottlieb drop target assemblies (found on pages 16 & 17) have very similar hardware.

If you know of any other games to add to this list or have corrections, please comment.

#2 2 years ago

Here are some before pics...

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#3 2 years ago

Unsoldered switches (1st pic) and removed entire assembly...

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Added over 3 years ago: Note: To remove the drop target assembly you can instead unscrew the switch stacks - less work than desoldering.

"Unscrew all the switch stacks one by one. Wrap each switch stack in low tack masking tape or thread a 5-40 nut onto each screw to hold the switch stack together."

#4 2 years ago

Removed single switch and two brackets...

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#5 2 years ago

Unscrewed switch stacks from other side...

Notice two rubber grommets #986 missing from target slots 1 & 7.

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#6 2 years ago

Two pics below showing the three kinds of springs...

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#7 2 years ago

Removed switch plate (4 screws)...

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Top guide plate loose now and can slide forward...
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#8 2 years ago

Close-up with plate off...

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#9 2 years ago

Next, I used a screwdriver to push all 7 springs attached to drop targets off of each trigger...

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#10 2 years ago

Next, I removed bottom guide plate by first flipping over and removing two screws that hold it in place.

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Then I detatched springs from triggers again and bottom guide plate was separated.

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#11 2 years ago

Flip over and now top guide plate and targets together can be taken off of triggers.

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#12 2 years ago

I think that Volley could be added to the list.

#13 2 years ago

Pro Football, Magnotron/Duotron, and Too Card should be pulled from the list as they dont have drop targets.

#14 2 years ago

If you plan to do many drop target banks a spring hook tool comes in handy for getting the springs back into place.

#15 2 years ago
Quoted from MikeO:

Pro Football, Magnotron/Duotron, and Too Card should be pulled from the list as they dont have drop targets.

Thanks Mike, makes sense - removed from list.

#16 2 years ago
Quoted from MikeO:

If you plan to do many drop target banks a spring hook tool comes in handy for getting the springs back into place.

I'm new enough to EMs that I haven't even heard of this tool and tools are important - thanks for mentioning. Do you have a link to an example of this tool?

#17 2 years ago
Quoted from D-Gottlieb:

I think that Volley could be added to the list.

Ipdb lists Volley as being made in Oct, 1976 and manual says this specific assembly was used up to before Dec, 1974 but I can check my Volley later.

#19 2 years ago

Thanks for posting links.

Found this one too: amazon.com link »

#20 2 years ago

OK, let's continue to take apart. Normally I don't think you would have to go to this extent, I'm just doing it to do it

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I used pliers to push off retaining ring:
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Then pulled out rod:
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#21 2 years ago

Q: What tool is best for taking off retaining rings?

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#22 2 years ago
Quoted from spinal:

Q: What tool is best for taking off retaining rings?

Push them off with a magnetic screwdriver inside to keep them from flying into invisibility.

#23 2 years ago

Don't take the coil mounting bracket off of the main frame. It is factory set for the plunger to correctly bottom out to the coil stop. Once you take it off you will have to make an adjustment that is not totally obvious to get it back correctly.

#24 2 years ago

Sorry Mike, already done but at least I took lots of photos (and I think it was level and pushed all the way to one end). Anyway, I know for next time - thanks.

#25 2 years ago

Took 4 screws off with 1/4" nut driver.

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#26 2 years ago

Next the brackets...

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#27 2 years ago

Then I noticed none of my hex keys fit so had to order a larger set with a 9/64" hex key before I could take apart. But Amazon prime is amazing these days - often one or two days and free shipping.

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#28 2 years ago

So got 9/64" hex key and took apart...

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#29 2 years ago

Above you can see I ohmed out each coil with a multimeter and got 12.6 and 12.8 ohms which I think are good for A-5196 but not 100% sure as it was not listed on the list I have of coil resistances.

Does anyone know of a coil resistance sheet that has the resistance of A5196 listed on it to confirm 13 ohms?

#30 2 years ago

I feel bad now. These before look far better than mine do after (except my targets are new). My before was pretty bad though.

Pioneer (so I'd assume Spirit of 76 and New York) also use the same setup for their drops.

https://www.flippers.com/coil-resistance.html says A-5196 is 13R0.

#31 2 years ago

Does your Pioneer have a stepped reset arm like this pic?

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#32 2 years ago

Also, thanks for confirming 13 ohms - I will print out that coil resistance chart as well.

#33 2 years ago

Now regarding the coil stops, I noticed the nuts are different and I can only remove one of them...

I'm curious as to which of these (if any) are factory. Anyone know?

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#34 2 years ago

On the other one, when I turn the bolt, the inside of the stop rotates along with it. So even if I hold stop with pliers, the inside rotates as I turn nut.

Anyone have any idea how to take this off?

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#35 2 years ago
Quoted from spinal:

Anyone have any idea how to take this off?

If you are replacing the stop, with a new one. Then a Locking Vise Grip and a socket/ wrench. Twist it, it may just snap off on the threaded part.

#36 2 years ago

The one you can't take off is factory. The shaft is peened so you can't.

The other is a Gottlieb stop but the nylon bushing may be a bit small for the hole. Shouldn't matter in the grand scheme of things.

The most you can do is look for a replacement from a spare part. PBR probably won't have it.

#37 2 years ago
Quoted from spinal:

Sorry Mike, already done but at least I took lots of photos (and I think it was level and pushed all the way to one end). Anyway, I know for next time - thanks.

Your goal is to have the plunger bottom out just as the drop targets rise above the frame and catch on top of the frame. Adjust the coil too tall and the targets won't push up high enough to catch. Adjust the coil too low and you run the risk of breaking the stop tab off the bottom of the targets.

You should have some evidence of where the screws were positioned relative to the slotted holes to get them close to where they were to begin with.

Good luck.

#38 2 years ago
Quoted from spinal:

Does your Pioneer have a stepped reset arm like this pic?

No, it doesn't, so the mount of the coil is slightly different, but the rest of the mechanics including the series bar is the same.

#39 2 years ago
Quoted from MikeO:

Your goal is to have the plunger bottom out just as the drop targets rise above the frame and catch on top of the frame. Adjust the coil too tall and the targets won't push up high enough to catch. Adjust the coil too low and you run the risk of breaking the stop tab off the bottom of the targets.
You should have some evidence of where the screws were positioned relative to the slotted holes to get them close to where they were to begin with.
Good luck.

Thanks for this as now I know how important the positioning is here - I will strive to put them in the exact position as I found them.

#40 2 years ago
Quoted from MikeO:

The one you can't take off is factory. The shaft is peened so you can't.
The other is a Gottlieb stop but the nylon bushing may be a bit small for the hole. Shouldn't matter in the grand scheme of things.
The most you can do is look for a replacement from a spare part. PBR probably won't have it.

Didn't know that these were peened on - I have only encountered ones you can replace and assumed that when one rebuilds coil assemblies that you replace the stop.

#41 2 years ago

Again, just taking everything apart to this extent mostly as a learning exercise and not because it's necessary.

To that end...

By what means do I take the coil plunger off of the reset arm? (yes I'm going too far but I'm curious - hah)

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#42 2 years ago
Quoted from spinal:

Again, just taking everything apart to this extent mostly as a learning exercise and not because it's necessary.
To that end...
By what means do I take the coil plunger off of the reset arm? (yes I'm going to far but I'm curious - hah)

You can use a nail and a hammer, but if you want to reuse the pin and not damage the plunger, you'll need a pin punch, similar to the one you'll need to remove the flipper links from the pawls, if not the same size. I use flat punches, but the ones with the centring pin would be easier.
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Put it on a vice or a hole in your bench so the pin has somewhere to go and then tap it through.

#43 2 years ago

I found that the easiest way was to get a small 2 by 4, drill a hole into it, place the joint in the hole and knock the rollpin out with a hammer and punch.

Good guide so far. When I rebuilt the droptarget banks on my Hot Shot, I didn't unsoldier anything, I just unscrewed the switches. I found it easier due to my horrendous soldering skills. :p

#44 2 years ago

I will post up this link
http://www.pinwiki.com/wiki/index.php?title=EM_Repair#Drop_Targets
Just to supplement.

#45 2 years ago

Great resource - thanks for posting!

#46 2 years ago

Removing the 5 rubber grommets from switch plate (2 were missing for me). Pull away from slot side as seen in pic and they come out easily.

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#47 2 years ago

Now removing springs. I have a spring hook tool on order so for now used end of my hex key which has slot.

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NOTE: the two sets of 7 springs are *not* the same even though they look the same upon first glance - they have different tensions so don't mix them up.

#48 2 years ago

Those grommets are unobtainium as far as I'm aware. I haven't been able to track down a substitute where I live either.

PBR has had gtb-986 grommets since late 2015.

#49 2 years ago
Quoted from ajfclark:

Those grommets are unobtainium as far as I'm aware. I haven't been able to track down a substitute where I live either.

#50 2 years ago

Cleaned metal parts with brush and Simple Green deluted to 1/10 which I keep in separate spray bottle followed by a bit of dish soap at end.

What do you recommend for cleaning off greasy metal parts?

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