That capacitor on the reset pin may not be terribly critical, I'd expect
anything from 1 mf to 10 mf would work adequately because electrolytics
have very loose tolerances anyway.
An open capacitor on the +5 volts will keep the processor from executing
correctly also.
73, Jerry, K0CQ
On 1/20/2011 8:52 PM, Don Rasmussen wrote:
Thanks Dr. Jerry,
I swapped the 68C05 into another radio and it works fine. There is 5V on the
pins where it is required, and I can hear the crystal oscillating using an
external receiver. All this, plus the fact that it worked intermittently for a
couple cycles before it finally stopped working seems to indicate that the
capacitor on the RESET pin may not be allowing the processor to do a reset at
power up. I'll try to find something near 2.2 mf to test with and order the
proper part if that works. Thanks for the info. Don.
=====================================================
The counter, display driver, and keyer are all done by a 68C05 on the
display board. It fails when the electrolytics go bad. It can also fail
from loosing power from a dirty board connection. It doesn't control any
of the radio, so everything else will work without the display, just you
don't know easily here you are tuned. History says replacing the
electrolytic or two on that board usually fixes it. Order up the lowest
ESR, highest temperature rated one from Mouser or Digi-Key to get the
longest life.
73, Jerry, K0CQ
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