Part one of term paper
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 what may be failing, and it¡¦s a very handy measuring device used to determine ...

Part two of term paper
... IC. If the voltage is LOW, the bottom LED lights. If the input voltage is HIGH, the top LED lights. When the input probe is disconnected, both LEDs light. Note that pin 3 of the 555 IC always goes to the opposite logic level of the input. Therefore, if the input is HIGH, the output of the 555 IC, which is pin 3, goes LOW. This in turn activates and lights the top LED (the HIGH indicator). Logic probes derive their operating power from the PCB under test. Care should be taken in attaching the clips t ...