Williams System 3 thru 7 Driver Board


Price: $199 – Driver Board

Price: $375 – Main Board and Driver Board

Machine Name

This is a designed to be a drop in replacement for all Williams System 3 to 7 pinball and shuffle bowler games using the original MPU board, or direct connection with the pinballpcb Main MPU Board.  Like all the other Kohout Enterprises’ boards, obsolete components have been designed out, when possible,  and up to date devices are used.  The board includes a 30 day unconditional guarantee and a 1 year repair/replacement warranty.* (See detail at bottom of page.)

Some Improvements to the original are as follows:

  1. Added 40-pin connector for direct connection to replacement Main MPU Board – A standard 40-pin IDE connector has been added to bypass the large, problematic Molex connector.  If mated with the Replacement MPU board, the large Molex connector is not needed and is not recommended.
  2. Simple Diagnostic LED’s added for troubleshooting – All Inputs and Outputs have LEDs for easy detection of a malfunctioning driver or input.   This can greatly reduce troubleshooting time required to fix a simple problem.
  3. Large, problematic, and often fried resistor required for lamp drives have been designed out for simple MOSFET drivers. 
  4. 100V NMOS and PMOS Transistors have been used for all outputs.  This reduces component count and, more importantly, power and heat dissipation.
  5. Active Drain to Gate clamp protects solenoid driver MOSFET outputs.  This circuit protects the MOSFET even when diode on coil have been removed or becomes disconnected.
  6. Thicker PCB for improved durability – 0.093″ instead of 0.063″

Each board comes complete with the replacement board, schematics, board layout drawings,  instructions.

This board will work in the following games:

Kohout Enterprises System 3-7 Replacement Driver board 
(Click Picture for Larger View).
Kohout Enterprises System 3-7 Replacement Mated with Original Williams MPU Board 
(Click Picture for Larger View).
Kohout Enterprises System 3-7 Replacement Mated with Kohout Enterprises MPU Board 
(Click Picture for Larger View).
Replacement System 3-7 Board uses a 0.094″ think board instead of the original 0.063″, which makes it much for rigid.

Technical Details

Coil Diodes:   The use of the diodes on the coils is to provide a discharge path for the inductive current when coil turns off.  When the coil turns off, the voltage tries to go high, but the diode clamps the voltage to one diode above the solenoid supply and dumps the energy into the solenoid supply.  Without the diode, the voltage would, in theory, go to infinity, but what really happens, is the Bipolar output transistor breaks down and causes damage.    Once this occurs, the device typically will not work again.

On this replacement board, an 47V zener clamp has been added between the Drain (Output) and the Gate of the MOSFET.  If the diode is present on the coil, then the clamp never turns on.  However, if the diode is ever removed, when the MOSFET turns off, the voltage goes high on the drain.  Once it reaches 47V, it turns on the MOSFET to dump the energy of the coil to before it can reach the breakdown of the MOSFET.  100V MOSFETs are used, so the clamp is half the rated voltage of the output device.  With this topology, the energy is dumped to ground instead of supply.

Lamp Drivers:  As can be seen, the large 27 Ohm resistors have been designed out, since MOSFETs have been used.  Since the original devices were Bipolar Transistors, they needed a large amount of base current to supply the required collector current.  The power dissipated in resistors was completely wasted and was not used to supply the lamps.  The total power dissipated was normally 24 Watts  (8 Lamp drivers at 3 Watts Each).  The lamp driver current was measured and the original Williams Board was approximately 5.5 Amps with all the lamps on.  The current measured with the Replacement board was only 3.5 Amps, a drastic 2 Amp decrease!