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Logic Probe is one of the basic troubleshooting tools for common electronic logic circuits (TTL circuits). Almost all video game circuit boards are built using TTL chips. These chips will occasionally fail and the Logic Probe is a tool that affords us a look into ....

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.... top LED (the HIGH indicator). Logic probes derive their operating power from the PCB under test. Care should be taken in attaching the clips to safe voltages; you may want to first use a Volt Meter (Digital Multi Meter) to verify the hook up points have good voltages. The four diodes protect the IC from reverse polarity. Capacitor C1 prevents transient voltage from affecting the logic probe when the black lead is not connected. Pin 5 of the 555 IC is grounded through resistor R1. The logic probe will indicate a HIGH for 2V or greater, and a LOW for 0.8V or less. To use this logic probe, follow the procedure. 1. Connect red power lead to +5V of circ ....