KPC2.1 KANTRONICS KPC-2 CLOCK MODIFICATION ----------------------------------- I have a Kantronics KPC-2 TNC and noticed that the internal software clock (accessed by the DAYTIME command) would speed up over a 24 hour period. Use of the DAYTWEAK command to slow down the clock to an acceptable accuracy proved of no use. Since I planned to use the TNC continuously and did not wish to be bothered with having to correct the 10 to 15 second error each day or have the error accumulate over a longer period of time, I decided to modify the TNC to solve the problem. I determined that the CPU clock was running too fast and thus caused the timing cycles used by the internal software clock to be too short. Using the DAYTWEAK command to slow down the software timing intervals had little effect since the CPU oscillator was so far off that even setting DAYTWEAK to 15 wouldn't bring the DAYTIME clock within acceptable adjustment range. To correct the problem, one must slow down the CPU clock oscillator. To do this, open the KPC-2 case by removing the two front screws and removing the front panel and bezel. You will find a screw on the upper right hand corner of the case which holds the 5 volt regulator chip; remove this screw. Pull the circuit board straight out of the front of the case. Holding the board with the front toward you, you will see the largest IC chip, the 63B03 CPU, U8, on the board in the middle, located somewhat to the left of center. Just behind the right side of the CPU is the 7.3728 MHz crystal for the CPU oscillator clock. Near this crystal should be printed a half-moon shaped area for a trimmer capacitor, C33, which Kantronics decided was not necessary, so it was omitted. It is at this location, C33, in which I soldered a capacitor to correct the clock speed. I used a 47 pf (picofarad) ceramic disc type capacitor with an NP0 rating. CONTINUED IN KPC2.2