Quoted from cottonm4:
I have my theories that I got to employ when I was building my Star Gazer pin.
I'll start this way. Remove your drop target assembly from the pin and place it on your workbench where you can manipulate the targets manually.
Using the lever, raise your targets into the up position. Did any one of them fall? Now, knock them down with your finger. Pretend your finger is a silverball and give them a good hard snap. Did any one of them brick? I am guessing the answer to both actions is going to be no. Keep doing this test until you are satisfied that your drop assembly is assembled correctly and that the targets are acting correctly.
Once you are 100% happy with the target action on the work bench, then reinstall the drop assembly in the play field.
You only have 2 places you need to look at. Keep in mind that Stern did NOT assemble these 40 year old pinball machines with accuracy.
First item up: You have one or more targets dropping prematurely. Keep in mind that your targets were working fine on the bench. And now they are not. Check to see how much clearance there is between the front of the drop target and the slot the targets set in.
If you have no clearance between the target and the slot then here is what is happening: When the lever raises the targets back up it sort of shoves them forward a little bit. Then the errant target will brush up against the wood in the slot and get "pushed" back down. What you want is .010" to .020" clearance between the wood in the slot and the front of the target. You want the target to be able to raise up freely and not interfere with anything, including the wood in the slot.
Here are the 3 drops in my Seawitch.
This is 3-drop on lower left of play field.
As you can see, there is lots of clearance between the target faces and the wood in the slot. This set works fantastic.
Next up is the 4-drop in the middle of the play field. These drops also work well. But if you look closely, you can see that there is a larger gap between the upper target face and the slot while at the lower target there is not as much clearance ( remember, Stern was not working to high precision ). But there is enough clearance for the targets to stay up properly.
Last up is the upper 4-drop in upper right side of play field. And if you look carefully, you will see that all 4 targets on this assembly are nested right up next to the slot. The top drop target does have some clearance that you can barely see. The other 3 targets are nested right up to the slot. But this target assembly also works well. These 3 targets come right up to the slot but they are not pushing against the slot. So, while they are touching the slot it is not enough to cause premature target dropping.
So, how do you fix it? You have 4 options.
1) You can reset the drop assembly by filling the holes in the play field and moving the drop assembly back about .020". But that is a cumbersome process if you don't know what you are doing.
2) You can your get a wood rasp and start removing wood from the slot in front of the target to gain clearance. I will advise you that trying to file/rasp wood from the slot will take a lot longer than you think. There is also the downside that as you a moving the rasp in a downward motion that some of the lower side play field veneer might start delaminating leaving you with splinters of woods and rough edges on the lower side of the slot.
Harbor Freight wood rasps work well for me.
3) You can get some heavy grit/80 grit sandpaper and a paint stir stick. Tape a strip of sandpaper to the stir stick and now you have a sandpaper rasp. It will be more gentle than the metal rasp but it will take a lot longer than you think for remove enough material to make a difference.
4) You can go nuclear and get out the Dremel Tool with the small sanding barrel. But you have to be very careful to not cut any gouges in the slot. If you are good with a Dremel this will be your fastest way to get the target clearance you need.
I have worked up a method for resetting the entire drop assembly and in most cases, filling the play field holes with dowel and moving the assembly back is my preferred approach for prematurely dropping targets.
That takes care of premature target dropping.
Now, we have to talk about bricking.
Let's go back to your bench test. I said make like your finger is a silver ball and start snapping those targets down hard. On the work bench, I bet you did not have any bricking going on, did you? But then you install the assembly back into your play field and the bricking starts happening. What has changed? Other than installing the assembly back into the play field, what has changed? Your drop assembly has not changed from the work bench to the play field. What is different? Why are the targets bricking only when the assembly is installed?
The only thing that has changed from the workbench to the play field is that there are now 3-4 posts and a rubber ring sitting behind the targets. Remember, Stern did not assemble these 40 year old pins with precision. Stern was downright sloppy.
This is not Stern, exactly. This is the repro Star Gazer play field. When I built this play field up, I ran into bricking problems with the left drop assembly.
Look carefully that this pic. What you cannot see is the back side of the target slot as it is hidden by the rubber ring. What was happening is another clearance issue just like the targets dropping prematurely. Now there is a clearance issue with the backsides of the targets and the rubber ring. What happens is when the silver ball smacks the target, the targets zings backwards right into the rubber ring, as which point the rubber ring bounces the target right back into its rest position.
Make this next check easy on yourself. Use some masking tape, or something similar, and make your self some tape handles for your targets. And mount the assembly to the play field. Now, push back on a target and see if it is making any contact with the rubber ring on the posts. The target should not touch that rubber ring. Rubber bounces and it will bounce that target right back into its rest position and you have a brick. Double check yourself and pull the target back up with the tape handle. If you see any contact with the rubber ring you need to eliminate that contact. And while you may think you are OK doing this test, consider the possibility that the target shaft might flex a bit when it gets hammered by the silver ball.
I had to make an undercut in the the left rail and move the posts back by one hole dimension. That solved the bricking problem on this set of drops.
Then the upper left drop assembly was giving me problems with both premature target drops and bricking. This was my experimental drop assembly where I figure out this dropping/bricking problem. I used methods #2, #3, and finally #4 listed above to correct the dropping issue. This was my drop assembly I figure this stuff out with; And if I had it to do over again, I would have filled the play field holes wire dowel and reset the drop assembly. Hidesight; You know how it is.
Anyway, after I fixed the dropping issue, I had to go after the bricking issue. And again, this involved moving the posts back by one hole dimension.
I did not get pics of moving the holes but that is not much to it. Fill a hole and then drill a new hole right behind the one that was filled.
I did what I have been telling you and all my target problems went away.
Here is one thing you might try to use to isolate a bricking issue. Remove the rubber ring from behind the targets and replace it with a couple of heavy rubber bands. They are thin and will give you extra clearance and will also keep the ball in control as you are knocking down targets. I would suggest removing any GI lights before you start banging away.