frenchmarky,
I did some investigating today. You’re correct; some of the ledges are shallower than others. I pulled out 5 drop targets and measured the ledges. The average ledge is about 0.080 except one target seems to be 0.054. It does appear to be sawed off. It’s also the only one with the “T” shaped foot.

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I like this suggestion, I used two part epoxy from Harbor Freight and the glue broke from the magnets in a few games also.
Used some dollar store super glue gel and no issues since.

Weird because that T one is from a Tri Zone, which indeed is a lot of single drop target units, but I can't figure out why it would latch reliably without the horseshoe spring either, since the exact same target in my BK without the blade-type spring failed to reset and stay up about 50% of the time. Is there something different in the design of the single drop units vs. the multi drop banks? -Or- something different between a sys 6 bank and a system 7 bank mechanics as far as latching, even if they might use the same T-type target?

Did anyone find a supplier for these discs that are the correct size?
Thanks.

So far everyone I talked to has had good luck with Gorilla brand super glue.

I broke a target trying to get the magnet off.

I gotta figure the glued magnets coming off must be from the target flexing as it is hit. Just the target falling and resetting doesn't seem like it would do it.

Finished my Gorgar and those NMP drop targets are great!!! Can't recommend enough!

Use these!
https://www.theclip.com/store/3m-vhb-double-sided-adhesive-small-round.html

I fixed it!

Some of the glue I used did not hold, am sure there is something that will work fine, but I decided to switch to using ring magnets and pop-rivet them on. Should hold forever.

I used these and so far they work reliably, no cases of missed drops:

https://www.magnetshop.com/neodymium-ring-magnets-p-2174.html

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Where can I order these from? The pin side shop is gone and they are back ordered on the troxel repair site. I want two 3 banks for Gorgar.

I have used these on two games. They work very well! Targets drop like it’s there job! Haha. I took a little metal file and gently roughed up one side of the magnet and used 2 part epoxy. I did not have an issue with magnets separating.

Contact me at [email protected] I have a free shipping sale going on this month.

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Ah sorry I must have deleted my post just as you posted, I had ended up ordering them from troxel repair even though they were back ordered. Thanks for the reply and awesome product though!

No problem noopy. I sent Troxel several boards last week. He should have them back in stock shortly.

Thanks for trying our sensor boards - You'll never go back to the old sliders.

Thanks for the order. They are in the mail. I just forgot to update the site that they were back in stock. Bob usually gets them to me pretty quick when I run out.

How's it been working with the ring magnets? I'm thinking of doing the same.

Awesome product! Just wanted to share a weird issue I had when installing a 4-bank board on Stellar Wars. After installing the board the first 3 drop targets in the bank that were hit would register, but not the last one, and also the "all down" series switch wasn't registering. Here's the weird part - it didn't matter which of the drop targets was the last to be hit - it could be any of the four - but it wouldn't register. I'll spare you the troubleshooting but the problem turned out to be a driver board issue. Swapping driver boards with another working game solved the problem, and both games worked.
I suspect that the issue was a bad 7406 at IC18, but I haven't had a chance to replace it yet. The main difference between these boards and the original boards with the horseshoe contacts is this: With the original setup when a drop target is hit that target's switch is momentarily closed, while a second switch (series switch to indicate all targets down) closes and remains closed. With these replacement boards when a target is hit both the target's switch and the series switch close and remain closed. For some reason my driver board didn't like that. Any 3 switches in that particular column could close and remain closed and would register, but then any additional switches in the same column would not register.

4 or 5 years ago when we were testing these drop target switches I was concerned about the momentary switch. See this thread:

https://pinside.com/pinball/forum/topic/replacing-williams-drop-target-sliders-with-reed-switches

I found that the drop target switches made no difference if they were held closed. All the other switches registered normally. Switches on the same column, same row, or any other column or row. I’m sure the problem you are experiencing is on the driver board.

Just wondering... on a normal board from this era, is there any limit at all as to how many switches it can handle and register closed simultaneously in switch test mode? I mean like if you physically held closed every switch in a column, or a row, or multiple rows/columns or even the entire game?

Williams was worried about the current draw on the switch matrix which is why they had resistors on the early driver boards in this circuit - and probably also why they did the momentary drop switch with the all-done signal like an EM would. The advantage to this setup is that the all-down signal does not depend on the game 'seeing' all the momentary switches. Bally/stern games if they miss a drop or the switch is dirty/not registering the bank could go down and stay down. (Later sterns mpu200 games solve this a little by letting drop switches reactivate, but since they were 'marked' closed, they do not score again.)

I don't see why the switch matrix couldn't read every single switch down physically. Sounds like an interesting experiment to take some jumper wires and connectors and try it out. I do notice that later games sometimes 'stagger' the switches that are likely to be closed so that they aren't all in the same column/row. Likely they were being overly cautious about how much current the transistors and chips could sink.

Probably fortuitous that their (and everybody else's) EMs really *had* to use momentary drop scoring switches, as far as Williams being able to stick with the same units and parts other than changing to gold contact surfaces. For a while anyway.