fault finder for ASCII keyboard

97 faultfinder for ASCII keyboard To be able to check the connections to an unknown ASCII keyboard, you want to know first of all where the supply voltage is connected. This can quite simply be done by removing the cover and tracing a pair of the wider tracks to the ICs. Next, the strobe connection has to be found. After the supply voltage has been connected, pressing one of the keys must produce a short (strobe) pulse at one of the output pins. If an oscilloscope is used to find this pulse, it will be seen at once whether it"s positive or negative. Once these preliminary checks have been carried out, the faultfinder can be used. Connect the outputs of the keyboard str f Strc Z 7-94 +5 5V BC 547B 83546 T1 as shown in the circuit. When one of the keys is pressed, a strobe pulse is produced which triggers the eight-stage bistable IC1. The signals present on the data lines to the faultfinder. Set the strobe input to positive or negative with switch Si. A positive strobe is connected ...