(Topic ID: 133404)

Knocker Assembly repair, tweaked?

By mark532011

7 years ago

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  • 5 posts
  • 4 Pinsiders participating
  • Latest reply 7 years ago by Don_C
  • No one calls this topic a favorite


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#1 7 years ago

Newbie question. I have a Game Plan Star Trip with a broken knocker assembly. In attempting to repair it, it looks strange and not like a normal solenoid assembly. So I have a couple of questions.

This is what the original looked like. It has an extra long tube (3")

Question #1 - how does it actually knock? there is a rubber bumper on one side which should not make much of a "knock" and nothing on the other side.

Question #2 - looking inside the tube, it looks like a wad of glue or something.. is this a seriously tweaked tube or is that the way a knocker tube is?

Question #3 - the tube has a small amount sticking out from the flange, is this an obtainable part? I don't see anything like it in the parts websites.

Any help would be appreciated!

#2 7 years ago

The plunger rests on the rubber part and produces a KNOCK when it hits the other metal end.

Coil and coil sleeve are shot - shorted transistor locked it on and fried it, most likely.

LTG : )™

#3 7 years ago

Thanks for the info!

#4 7 years ago

If you have a DMM you can measure the ohms across the coil. If it reads around 0 ohms, it's shorted. If it reads several ohms, and you like tinkering like I do, you may be able to knock the sleeve out (using a long socket or something) and widen the hole so a new sleeve will fit, and revive the coil. Otherwise, they're about $7-10.

#3, The sleeve is obtainable. Get one as long, or longer than yours (http://www.pinballlife.com/index.php?p=catalog&parent=14&pg=1) and cut down to size.

If you want or need a new coil, you may have to look in manual to determine a close replacement, from the available coils ...


For a knocker, just about any coil will work, as long as it fits in your knocker bracket.

You should probably test and fix the driving transistor before trying your new or repaired coil.


Here's some good substitute info for the coils:


#5 7 years ago

The 'wad of gum' is the melted coil sleeve. You will need a new coil, and a new sleeve. That sleeve is one piece, extending throught he coil. The small flange is at the top, and the longer part is at the bottom to guide the core.

That whole assembly is (probably) mounted so that the bracket and coil core (moving metal rod) are vertical, with the rubber pad at the bottom. Courtesy of gravity, the coil core rests on the rubber pad. When the coil is energized, the core is pulled up into the coil. As the core is moving through the coil, the power to the coil is switched off and the core continues moving up via its inertia, until it hits the upper bracket and makes the 'knock'.

If that bracket is mounted horizontally in the game, then you are missing a return spring, but then the core would have a flange on it for the spring, so I thnk it mounts vertically.

The transistor that energizes the knocker coil is also no good anymore (it's shorted), that's what caused the coil to overheat and melt the sleeve), and the pre-driver transistor that goes with the driver transisitor is probably also no good.

Hope this helps.

Don C.

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