@lyonsden:

Really absolute excellent post and write up.

Very helpful foto documentation - will help the whole pinball community for the eternity.

I think, you will be "pinwikified", if you write to Chris Hibler - this should be stored in pinwiki.

Another reed sensor as I suggested would also work, important is the length of the glas-tube, 7mm.

- MEDER, part-number: KSK-1A80-1015 = mouser.com part-number: 876-KSK-1A80-1015)
http://www.mouser.com/ProductDetail/MEDER-electronic-Standex/KSK-1A80-1015/?qs=KFo7JewZbUFX%252bU5EsD5Ziw%3D%3D

- PIC, part-number: PMC-0701 = conrad.de part-number: 503800-62
http://www.conrad.de/ce/de/product/503800/Mikro-Reedschalter-PIC-PMC-0701-1-Schliesser-05-A-150-VDC-120-VAC-10-W

Good idea, to also replace the diode, when you just have it open.

GPE should put it in his shop as a "repair kit for WMS 20-10293 reed sensor".

CONGATS and THANKS for your great documentation.

It is correct. We use here a normally open (make contact) reed switch. We do not have to abserve polarity. Both, north and south pole, switch equally.

I do not think, it does matter here in this application, BUT mightbe, I had the same luck at that time as you now had.

Look here
http://www.pic-gmbh.com/en/interactive/
there you can play a bit interactive - choose one pole and manual modus.

By the way- the disgusting old silicon or whatever it was, could be something like this:
http://www.acc-silicones.com/products/encapsulants.ashx

I think, the reed switch has to be mounted, as in the attached grafic.

REED SWITCH.GIF

I like, to draw grafics

REED SWITCH 1.GIF

REED SWITCH 1a.GIF

What I was always asking me, is, how the 2 little magnets must be arrranged. I have no idea of magnetic fields, but googled a bit and I could imagine, that they are arranged as shown in pic1 and function as shown in pic2.

Maybe someone, who has - others than me - properly taken care of in physics at school previously, can shed some light into the darkness.

REED SWITCH2.GIF

REED SWITCH3.GIF

Grafics-Update Have fun ...

REED SWITCH new.GIF

I now understood the operating principle of the 2 magnets. It is as follows:

As shown in the pictures, 2 magnetic plates , whose magnetic fields cancel each other, are mounted above each other. Between these 2 magnetic plates sits a "normal" reed switch.
If then a metal ball rolls above the unit, i.e. above the upper magnetic plate, the magnetic field of the upper magnetic plate is weakened . The magnetic field of the lower plate then dominates and can close the reed switch.

Pretty simple, isn´t it?

I am working on that too, but unfortunately, I have no 3d-printer. First problem is the housing, I am searching for that since years. Second problem are the magnets. I do not know, how strong they are and what are the exact dimensions. Next week I will order different magnets and will begin to test. I think, the strongness is not the problem in our application, as the 2 different magnetic fields cancel each other at first, until the balls rolls and the upper magnet field is weakend.
Interesting:
https://www.kjmagnetics.com/blog.asp?p=reed-switches-and-hall-effect-sensors
https://www.kjmagnetics.com/products.asp?cat=1

I do not know, how to measure the gauß of the magnets. Should look for I thing like this:

I am thinking about a very little pcb, lower magnet glued on the PCB, solder in the 2 parts, glue the second magnet on top and put all in a nice housing. E.G. see here: http://forum.mysensors.org/topic/909/reed-switch-normally-open-or-normally-closed

Easiest way would be to use a piece of wood, dremel it out and put in the magnets and the parts

Thats exact, what I am thinking of, but I do not have a 3D-printer ...

I am "playing" too

I do not know, if the original sensors are attracting the ball, BUT this is not good. I think, Bally/WMS calibrated the magnets so perfect, that it is exactly for the distance they need with the most less attraction. I think, I should take one of the switches out of my safecracker.

Momentary, I am thinking more about the housing.

A friend of mine made a 3D-grafic and we want to put it on a 3D-printer the next days and want to see the result.

Reed_switch_housing_(resized).jpg

Thats ABSOLUTLY correct - my grafics above are in this way misleading, as I drawed a playfield and not a plastic ramp or so. As far as I know, none of these reed switches is used through wooden playield. 3-5mm range should be OK, so the magnets could be weaker - my guess only.

What magnets did you use? Neodym or Ferrit? Neodym are much stronger ...

OOPS - thanks for the hint!!! Did not look under the playfield of my SC for a long time.

Here is an intersting link about magnets:

https://standexelectronics.com/products/permanent-magnets/