Page:Gametronics Proceedings.djvu/82

 5.)CATASTROPHIC FAILURE AT HIGH LINE OPERATION

This is nearly always a power supply problem caused by a marginal power supply design coupled with a high temperature environment. The use of a higher powered supply will not necessarily solve this problem since operating a power supply well below its ratings actually increases the voltage stress on the rectifiers, filter, pass transistor, and IC. The solution is to use a well designed power supply from a reputable manufacturer.

6.)Game Board Or Audio Signals Causing Spurious Video Signals

This usually occurs when the game board and/or audio board is operated from the rather crudely regulated 5 volt auxilliary supply on the video monitor and is caused by the lack of isolation between the auxilliary supply and the video power supplies. Signals from the game or audio board can couple directly into the video circuitry and even cause oscillations.

The best solution to this problem is to use a separately isolated power supply with electrostatically shielded transformer which will completely eliminate the problem. Other solutions are parasitic suppression and high frequency filtering of the auxilliary supply lines at some further degradation of regulation.

A similar problem of undesired interaction can occur when the games board and/or audio board use two or more different voltages from a common supply, such as in microprocessor applications. To avoid this problem, Adtech Power uses separate isolated secondary transformer windings and separate high frequency bypasses to prevent interaction. Additional filter circuits would eliminate this problem also.

7.)Static Discharge Failures

One of the major problems encountered especially in the new carpeted arcades is static discharge from players. Static discharge to the coin box will usually result in a free game. In fact, several juveniles have been caught using spark coils purposely to get free games from these machines. Frequently however, the static discharge will cause failure of the game. While a good power supply will not prevent these failures, the electrostatic shield of the transformer provides an excellent low impedance ground point for eliminating static discharge.

All external metal points including controls, switches, coin box, escutcheons, CRT shield, etc. should be tied as directly as possible with 20ga. or heavier wire to the electrostatic shield and 3rd wire ground. Note: Even controls with plastic knobs must be grounded since the high voltage (up to 40,000 volts on a woman with nylon clothing) discharge is sufficiently high to arc through the plastic knob to the metal shaft (ever touch a plastic light switch on a dry day?). Of course, a 3 wire line cord and outlet are necessary for this grounding to be effective.