(Topic ID: 204073)

Tech: GTB Sky Jump ball count unit (stepper) teardown & rebuild


By spinal

1 year ago



Topic Stats

  • 68 posts
  • 10 Pinsiders participating
  • Latest reply 1 year ago by spinal
  • Topic is favorited by 6 Pinsiders

You

Linked Games

Topic Gallery

There have been 109 images uploaded to this topic. (View topic image gallery).

image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg

There are 68 posts in this topic. You are on page 1 of 2.
#1 1 year ago

One of the main issues with my Sky Jump is with the ball count unit: it's not always stepping correctly to the next ball. As well, even if it does step to the next ball, often the backglass bulb for that ball does not light up unless I press on the back so the wiper makes better contact.

During this thread I will share my path through complete disassembly and rebuild of this unit. This will be the first time for me but in the end I hope to have a fully working ball count unit, but most importantly, I hope to be more comfortable with these types of stepper units in the future. There is no substitute for experience so the only way forward is just for me to do it and hopefully learn something along the way!

Of course, as always, your comments and suggestions are greatly appreciated!

Now, what little I know about steppers I have read from the very important website:

http://www.pinrepair.com/em/index2.htm#steps

which goes over the different kinds of steppers and how to fix them across the major manufacturers. I will be following advice from here so I want to say thanks in advance to those responsible for producing this great website.

This 1974 Gottlieb Sky Jump ball count stepper is of the Step-up/reset type which means one coil steps-up one by one and the other coil resets it all the way to the beginning. It is important to note also that very similar assemblies can be used for many different purposes so in the 1978 Parts Catalog (Volume P), you will find similar looking assemblies but not exactly the same as the ball count unit. In any case, this thread may be applicable to other stepper rebuilds like player units, coin units etc.

Here are some pics of the ball count unit in the lower-right corner of the backbox:

image (resized).jpeg
image (resized).jpeg

image (resized).jpeg
image (resized).jpeg
image (resized).jpeg

Another site worth mentioning:
http://www.pinwiki.com/wiki/index.php?title=EM_Repair#Step_Up_.2F_Reset_Stepper

#2 1 year ago

This Sky Jump came with a clip on the right side but not with one on the left side:
image (resized).jpeg

So I added this one on the left side:
image (resized).jpeg

But the question remains:

Q1: Did the factory often only put one of these clips on or was the left one lost at some point?

#3 1 year ago

Q2: Was there a Ball Count Unit sticker on the back of this unit when it left the factory? If so, can you post a pic of yours?

#4 1 year ago
Quoted from spinal:

Did the factory often only put one of these clips on or was the left one lost at some point?

No and Yes.

#5 1 year ago

The reason I ask is that other pins I have also only have the pin on the right and not on the left.

Here is my C37:
image (resized).jpeg
image (resized).jpeg

And here is my ACD:
image (resized).jpeg
image (resized).jpeg

#6 1 year ago

Duh, most people are right handed, too lazy/difficult to replace the left. you can see the wear marks on the left side...

#7 1 year ago
Quoted from spinal:

Of course, as always, your comments and suggestions are greatly appreciated!

I think one of the most important parts of the page you linked should be highlighted:

WARNING. This shoulder bolt has a nut on the back side. If this nut is not removed, and a big screwdriver is put on the shoulder bolt to turn it, the shoulder bolt will shear. This renders the shoulder bolt useless. If this happens nothing short of ordering a new shoulder bolt from Pinball Resource (part# a1059) will fix the problem. So the moral of this story is to first remove the nut from the shoulder bolt before removing/adjusting this bolt. (And even then during nut removal sometimes the shoulder bolt still shears.)

Before disassembling the whole unit, I would loosen that shoulder bolt, clean the pivot point (http://www.pinrepair.com/em/gtbcred1.jpg), etc and make sure the lever moves freely. I've found a lot of steppers that were completely non-functional only needed a bit of care at that one point.

#8 1 year ago
Quoted from spinal:

The reason I ask is that other pins I have also only have the pin on the right and not on the left.

I owned some EMs when they were new and they all came with both clips.

#9 1 year ago

Sky Jump is from 1974, not 1994.

The Volume P parts catalog you referenced is from 1978, not 1987.

Pay attention to ajfclark on the nut on the back side of the shoulder bolt. Other than that you can't really screw it up.

#10 1 year ago
Quoted from ajfclark:

I think one of the most important parts of the page you linked should be highlighted:

Before disassembling the whole unit, I would loosen that shoulder bolt, clean the pivot point (http://www.pinrepair.com/em/gtbcred1.jpg), etc and make sure the lever moves freely. I've found a lot of steppers that were completely non-functional only needed a bit of care at that one point.

Quoted from MikeO:

Pay attention to ajfclark on the nut on the back side of the shoulder bolt. Other than that you can't really screw it up.

Hah, you mean this one?

image (resized).jpeg

I had read that on pinrepair before as well but it was late last night and wanted to finish disassembly. Sheared very easily. Oh well, learned my lesson

#11 1 year ago
Quoted from MikeO:

Sky Jump is from 1974, not 1994.
The Volume P parts catalog you referenced is from 1978, not 1987.

Of course, changes made thanks Mike.

#12 1 year ago

If you are stuck for a replacement, in the past I have machined down a case screw from a PC using a drill and a file. Not pretty, but did the job.

20pcs-Desktop-Computer-PC-Case-Thumbscrews-Thumb-Screw-6-32-Black-Metal (resized).jpg

#13 1 year ago

==================
OK, let's begin disassembly:

Remove the two pins mentioned in post #2 above and unscrew the screw in the center of the image below. Use a magnet tool when removing screws (hold near) or they may end up falling down into cabinet. You can also place a towel over cabinet hole to prevent this but magnet tool works great.

image (resized).jpeg

#14 1 year ago

The assembly will now swing forward - here are some reference pics:

image (resized).jpeg

image (resized).jpeg

image (resized).jpeg

image (resized).jpeg

#15 1 year ago

My goal is to completely remove, disassemble and rebuild the entire assembly as a learning exercise and not just to fix the issue as fast as possible. I have no time constraints and am doing this for fun and I want to sit down and see how everything works together, including the switches etc. This is why I am desoldering all wires below.

If your goals differ, you may want to only remove the screws from the switch stack instead of desoldering those wires or you may even want to work inside the backbox while all wires are attached.

After desoldering and removing brackets:

image (resized).jpeg
image (resized).jpeg
image (resized).jpeg

#16 1 year ago

Before disassembly, here are some reference pics:

image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg

#17 1 year ago

I can almost guarantee you that at some point you're going to regret desoldering as much stuff as you are doing. It's really not necessary, you can clean those parts up without desoldering all that stuff.

#18 1 year ago
Quoted from EMsInKC:

I can almost guarantee you that at some point you're going to regret desoldering as much stuff as you are doing. It's really not necessary, you can clean those parts up without desoldering all that stuff.

You're probably right. Since it's my first time and I want to understand how all components work together while sitting down, it's a sacrifice I'm making this time.

#19 1 year ago
Quoted from spinal:

You're probably right. Since it's my first time and I want to understand how all components work together while sitting down, it's a sacrifice I'm making this time.

Just demount the switch stacks etc rather than desolder.

#20 1 year ago

Issue: Reset works fine (green) but after forward step (blue) it does not return fully to complete (red).

image (resized).jpeg

image (resized).jpeg

#21 1 year ago

First image is after reset and second image is furthest that stepper can progress forward:

image (resized).jpeg

image (resized).jpeg

#22 1 year ago

==================
Disassembly begins:

I started by removing the wiper assembly. Before removing the three screws, I marked the locations of the wiper cover plate with pencil.

image (resized).jpeg

image (resized).jpeg

image (resized).jpeg

#23 1 year ago

On the flip-side I noticed that the wiper fingers would not fully extend to the same height when depressed (2nd pic) - not good and probably the cause of why ball count lights in backbox were not coming on.

image (resized).jpeg

image (resized).jpeg

#24 1 year ago

At full reset I then marked the position of the wiper mounting spider in pencil so I would know where it was relative to shaft. Then I unscrewed with 1/8 hex key.

image (resized).jpeg

image (resized).jpeg

image (resized).jpeg

#25 1 year ago

Removed wiper base plate screws with 1/4" nut driver:

image (resized).jpeg

image (resized).jpeg

#26 1 year ago

Next I removed the switch stack (two screws). I agree with all the comments that it's easier to remove these screws beforehand without desoldering.

image (resized).jpeg

#27 1 year ago

Next I unhooked and removed the main reset spring. The pinrepair site said to count the number of times it unwound but it happened so fast that I wasn't able to. Hopefully this is not that important. Anyway if this old spring is weak and I'm replacing with a new one, this count wouldn't apply would it?

image (resized).jpeg

image (resized).jpeg

image (resized).jpeg

#28 1 year ago

Next I wanted to remove the nylon shaft bearing so unscrewed two 1/4" screws with nut driver. Was still tight to remove so also removed single screw for other metal piece there and then it came out (not sure what that adjustable piece is for).

image (resized).jpeg

image (resized).jpeg

#29 1 year ago

Next, I removed the step-up coil assembly with 9/64 hex:

image (resized).jpeg

image (resized).jpeg

image (resized).jpeg

image (resized).jpeg

image (resized).jpeg

#30 1 year ago

Then I removed the reset coil assembly:

image (resized).jpeg

image (resized).jpeg

image (resized).jpeg

#31 1 year ago

Next, I wanted to remove the reset arm so first I unhooked the spring:
image (resized).jpeg

Next, against my better judgement, I did a bad thing and took a screwdriver to the screw head:

image (resized).jpeg

... and the screw sheared off
image (resized).jpeg

Then I remembered having read not to do this on the pinrepair site:

"WARNING. This shoulder bolt has a nut on the back side. If this nut is not removed, and a big screwdriver is put on the shoulder bolt to turn it, the shoulder bolt will shear. This renders the shoulder bolt useless. If this happens nothing short of ordering a new shoulder bolt from Pinball Resource (part# a1059) will fix the problem. So the moral of this story is to first remove the nut from the shoulder bolt before removing/adjusting this bolt. (And even then during nut removal sometimes the shoulder bolt still shears.)"

It was late and I wanted to finish and rushed it. Anyway, this piece (A-1058 for Sky Jump, A-1059 is a bit longer) is available at pbresource for around $2.50.

Thanks to pinsiders ajfclark and MikeO who tried to warn me earlier in this thread but I had at that point already done it.

Newb lesson learned

#32 1 year ago
Quoted from spinal:

Anyway if this old spring is weak and I'm replacing with a new one, this count wouldn't apply would it?

There should be no reason you would have to replace that spring.

#33 1 year ago

You're not the first, and won't be the last. You may also have found it sheered off anyway. I'm sitting at 50/50 over 2 machines on that nut sheering the bolt.

Here's a pic of the quick replacement I made from an old PC case thumb screw:
16123238_268544953558420_436900583203405824_n (resized).jpg
The shoulder was marginally too big so I put it in the drill chuck and filed it down a bit.

#34 1 year ago

Yikes! What's next, a complete score motor switch overhaul?

#35 1 year ago
Quoted from HowardR:

Yikes! What's next, a complete score motor switch overhaul?

I think AS relay will be next but you never know

#36 1 year ago
Quoted from MikeO:

There should be no reason you would have to replace that spring.

I purchased one of Steve's spring kits awhile back (KT-GSTEP-01): http://www.pbresource.com/springkit.html

I assumed since they made these kits, that collectors must replace springs when they rebuilt but I am slowly learning that might not always be the case.

For this reset spring, I guess even if it got weaker over they years one could just wind it up tighter and get the same result right?

(that's why I'm doing these threads as it's the only way I can learn what other collectors are doing when they restore - thanks)

#37 1 year ago
Quoted from HowardR:

Yikes! What's next, a complete score motor switch overhaul?

I have done that, twice. Sheer lunacy. However, I didn't desolder the switches when I did it. I just unscrewed them from the mountings. Used a dremel wire wheel to clean them all up.

The motors I did them on were really grungy, that's why I did it. I've disassembled stepper units like this guy is doing, but I do not desolder the switches. Doesn't need to be done.

This is from a Drop A Card I did, before and after.

20150624_205931 (resized).jpg20150619_200052 (resized).jpg20150611_224303 (resized).jpg20150531_131234 (resized).jpg

1 week later
#38 1 year ago

Very nice - looks great!

#39 1 year ago

Came across this post which mentions 4 windings is standard for the return spring (need this info later). Also backs up that springs often don't need replacing.

Quoted from TimMe:

For all GTB small steppers made from the late 1940s through 1980, the torsion return spring on the stepper gear shaft should be wound exactly four times around and then attached to the frame spike.
As others have noted, the original unmodified drive spring should have more than enough power to index the stepper forward, and the torsion return spring should have plenty of power to return the stepper to the zero position, once the stepper is clean and lubricated and assembled correctly.
I also just want to mention that many times a spring will lose almost none of its "springiness" over time unless someone has manually stressed it beyond its normal operating range. The drive spring and torsion return spring used on the GTB small stepper are good examples. I've rebuilt many of these steppers on late 40s and early 50s games, and the original springs are nearly always in excellent operating condition.

4 weeks later
#40 1 year ago

2 weeks later
#41 1 year ago

Back again... took a break from posting as I had wait for parts etc so continuing now with disassembly:

-----------

image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
Remove remaining springs
image (resized).jpeg
image (resized).jpeg

#42 1 year ago

Alchohol swab and dremel to clean switch stack

image (resized).jpeg

image (resized).jpeg

#43 1 year ago

When wipers are ground flat like this they have more trouble sliding smoothly over rounded rivets. Brand new wiper from PBR on right.

image (resized).jpeg

#44 1 year ago

Wiper finger bushings also get gummed up so I cleaned with pipe cleaner. Fold to get thickness, dip in alchohol and clean out. New springs and wiper fingers ready to go.

image (resized).jpeg

image (resized).jpeg

#45 1 year ago

At one point tried to smooth out disc rivets but then decided to buy new rivets. Because of lack of riveting tools and the fact that so much time went but I just buckled and added a new disc from PBR. Fifteen bucks and boom, done. Still planning on getting tools so I can change rivets but ran out of patience for now.

(I realize it's a bit overkill but my goal was to go through the learning experience and have a minty fresh stepper when I'm done so I'm not recommending that everyone go to this extent )

image (resized).jpeg
image (resized).jpeg

#46 1 year ago

After cleaning parts with 1/10 diluted Simple Green, it's time to reassemble...

Now regarding springs, I purchased a new set from PBR. Above posts have mentioned that most of the time springs don't need to be replaced and that's what I've (finally) learned for myself as well. I already had ordered the springs so I used some for reassembly but like I said, most probably unnecessary so thanks for your comments

image (resized).jpeg
image (resized).jpeg
image (resized).jpeg

#47 1 year ago

Placing on arm and springs

image (resized).jpeg
image (resized).jpeg
image (resized).jpeg
image (resized).jpeg

#48 1 year ago

Attached new return spring (original below).

image (resized).jpeg

#49 1 year ago

New shoulder bolt to replace one I sheared off

image (resized).jpeg

Cleaning with pipe cleaner and alchohol
image (resized).jpeg
A bit of Teflon lube for metal to metal - inside hole as well
image (resized).jpeg
Screw first but not too tight
image (resized).jpeg
Then bolt on back to secure
image (resized).jpeg

#50 1 year ago

Attach spring and feed reset plunger through hole

image (resized).jpeg
image (resized).jpeg

BTW, plungers sanded smooth with 600 grit then polished with mothers mag polish.

Promoted items from the Pinside Marketplace
750 (Firm)
Sale Pending!
Chelsea, MI
Wanted
Machine - Wanted
Tabor, NJ
$ 125.00
Cabinet - Toppers
Sparky Pinball
From: $ 7.60
Cabinet Parts
PinBoltCaps
$ 76.95
Cabinet - Shooter Rods
Super Skill Shot Shop
$ 28.00
Playfield - Other
Pin Monk
$ 66.95
Cabinet - Shooter Rods
Super Skill Shot Shop
$ 76.95
Cabinet - Shooter Rods
Super Skill Shot Shop
$ 48.00
Playfield - Toys/Add-ons
ModFather Pinball Mods
$ 90.00
Lighting - Under Cabinet
Rock Custom Pinball
$ 11.95
Playfield - Toys/Add-ons
ULEKstore
$ 209.99
$ 8.99
Lighting - Other
Pappy's Pinball Palace
$ 239.00
Cabinet - Toppers
Tilttopper
$ 5.00
Playfield - Decals
Doc's Pinball Shop
$ 4.00
Electronics
Z-connector (24 pin) Out of stock
Professor Pinball
$ 159.99
Lighting - Other
Lighted Pinball Mods
$ 21.00
From: $ 175.00
Gameroom - Decorations
Pinball Photos
$ 200.00
Lighting - Interactive
Professor Pinball
$ 229.99
There are 68 posts in this topic. You are on page 1 of 2.

Hey there! Got a moment?

Great to see you're enjoying Pinside! Did you know Pinside is able to run thanks to donations from our visitors? Please donate to Pinside, support the site and get anext to your username to show for it! Donate to Pinside