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Hardware: Q*bert Knocker

Hardware Home | Computer & Monitor | Controls | Accessories
Pinball Plunger Circuit | Q*bert Knocker


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Q*bert Knocker Circuit Overview

Gottlieb designed Q*bert to activate a knocker assembly when Q*bert or Coily falls off the maze, which added the feel of the characters hitting the bottom of the game cabinet. Pretty cool stuff!

Brad Oldham has modified the MAME Gottlieb driver code to flash the NUM and CAPS keyboard LEDs simultaneously to simulate when the original Q*bert game activated a pinball knocker assembly. This opens up the possibility to drive an actual pinball knocker assembly from the LED signals.

I found this modification to be a very simple add-on to my existing I-Pac I'm already using in my cabinet.

*** MAME Dev Team: Please add this function in the official release code.

I modified my existing LED Driver Circuit to incorporate a portion of the knocker circuit. I'm utilizing the unused Scroll Lock input/outputs to drive my external knocker assembly. The remaining of the circuit is on a separate schematic. See schematics below.

I based my knocker driver circuit directly from the Q*bert service schematics. See below.

John's Retro Arcade Switch to Power Q*bert Knocker
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SW1 in the open position allows me to manually turn off the knocker circuit. The switch is necessary to protect the solenoid if the computer's CAPS lock is enabled during normal operation of the PC. If not, the knocker solenoid would seriously overheat and blow the fuse. Simply close SW1 when you want to play Q*bert. Connect the SPST switch between X2-1 (Knocker enable) and X2-2 (shared CAPS input from I-PAC).

Default Game Properties - Miscellaneous Tab
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Brad Oldham has his modified source code and precompiled version of MAME32.74 available on his site. I have created a source code patch file that you can run to modify existing Gottlieb MAME driver code. It is available in the downloads section which should also hopefully work for future changes of the Gottlieb driver.

In order for this circuit to work, you must enable LED support in MAME32. I have included a snapshot of the correct setting for MAME32. Brad Oldham states, "Ensure the RDTSC timing system in enabled." I have perfect results with RDTSC disabled. Actually, I have sluggish, weird joystick performance with RDTSC enabled on my machine. You may have to experiment with this yourself.


Q*bert Knocker Circuit Parts List

L1 A-5195 Gottlieb/Premier Coil P/N# A-5195 (Marco Specialties)
Q2 2N6045 Transistor (TIP 102 will work) P/N# 2N6045 (Marco Specialties)
D1 Diode usually included on the A-5195 coil (Marco Specialties) If not - Add 1N4004
SW1 SPST Switch (Radio Shack)
C33 0.1 uF 200 volt radial capacitor P/N# C_1M200VR (Marco Specialties)
R1 1K Ohm Watt Resistor P/N# 271-1321 (Radio Shack)
R4,R5 10K Ohm Watt Resistor P/N# 271-1335 (Radio Shack)
F6 1 Amp Slo-blow Fuse P/N# 270-1021 (Radio Shack)
PS1 P/N # 273-1668 (Radio Shack) 30VDC AC-to-DC Adapter
Knocker
Assembly
Knocker assembly off an old pinball machine (Rebuild using the A-5195 coil)

Q*bert Knocker LED Circuit Schematic Modifications

The following two schematics make up my current configuration using my modified LED driver circuit.

LED Knocker Schematic
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Knocker LED Driver Circuit
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Q*bert Knocker Miscellaneous Pictures

LED Driver Boards
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Knocker LED Driver Board
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Knocker Power Supply
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Knocker Cabinet Inside View
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