Stern’s new step-up driver board.



(World Poker Tour, Pirates, Family Guy, Spiderman and more to come!)



The SAM system was designed to control an optional ticket dispenser or knocker.  A low power driver transistor (Q24) has been reserved on all SAM machines to be used for these “optional coils”.  Unfortunately low power drivers use 20 volts or less.  20 volts isn’t enough to produce a loud knock.  In contrast Williams used 50 volts on their knockers to produce a really loud knock.

A “step-up driver” is needed to drive the knocker coil with 50 volts.  Rather than re-invent the wheel, Stern‘s new 50 volt step-up board will be used.  This board was first introduced in WPT.  It was designed along with the SAM board set and is easy to hook up.

These plans were worked out after consulting with Pat from Stern’s tech support line.   There may be “better” ways to complete this mod, but this one works just fine.


- Wire (~20 gauge), molex connectors and contacts

- Knocker assembly (Data East/Sega #500-5081-00)

- Knocker strike plate - SP01

- Stern step-up driver board part number 520-5254-00


The knocker and step-up board need to be connected to the following existing voltages and signals in the cabinet.  Be careful when routing wires, so they don’t interfere with raising and lowering the playfield or get caught on any assemblies.  Route wires along with existing harnesses - even if they have to be a lot longer to do so.  Your goal is to make the new wiring blend into the machine.

50 volt DC (coil voltage): 50 volts can be obtained by making a connector adapter (preferred) or by simply soldering to a convenient high power coil under the playfield.   Carefully route this wire in with the factory harness and back to the knocker.

Ground: Use a screw that fixes ground braid to the cabinet side or other suitable mounting location.

Q24 driver: This violet/gray wire comes from Q24 on the main driver board and is used to trigger the knocker. You can find this wire in a small, unused white connector inside the cabinet; near the coin door and tilt assembly. The red wire in this connector won’t be used.


Important:  verify the location selected will not interfere with the playfield components or service rails when the playfield is lowered.

Select a location to mount the knocker assembly and strike plate in the cabinet.  Make sure the plunger can make almost a full stroke before it hits the strike plate.  Be sure to cut the diode from the coil as it is not needed.

Mount the step-up driver PCB near the knocker and wire it all up as shown in the diagram. 

Once everything is wired up and in place, you just need to make a couple of changes in the SAM menus. Select “knocker” in the Q24 options. Turn the software knocker volume to “off”.

Sega/Data East knocker assembly

The knocker and step-up driver assembled on a small block of wood.  The 16 gauge wire is overkill and looks terrible when soldered.  Stick to 20 GA if available...

If you are feeling lazy, you can tag on to 50 volts by soldering directly to the hot side of a coil lug.  Making a plug-and-play connector adapter is a cleaner way to do it.

Completed assembly installed inside the cabinet.  Notice the striker plate is attached to the side of the cabinet.   The block of wood lifts the knocker above the angle molding at the bottom of the cabinet.

Wiring Diagram

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