Ed,
Put the K2 into CAL FCTR mode and check the voltage at U6 pin 3 - it should
swing from 0 to 4 volts when tapping the BAND+ and BAND- buttons.
Similarly, U6 pin 1 should swing from 0 to 8 volts. (If you read almost 0
volts and almost 8 volts all is OK).
If you have the correct voltage swing at U6 pin 3, but not at pin 1, the
problem is likely to be found on the thermistor board - if the voltage swing
is not good at pin 3, the problem lies in the 12 bit DAC or in the signals
coming from the MCU.
If the voltage swings at U6 are OK, then check the path through R19 and RP2
to the cathodes of the varactors. Look at the schematic to see 'which parts
are connected to what'. Be certain the diodes are correct (D17 has a
smaller body than D16) and that all connections are well soldered. "When
you have finished checking your soldering, check the soldering" - it is the
most common cause of problems.
73,
Don W3FPR
- Original Message -
Spent all of yesterday trying to figure out the problem with the low range
value during the PLL reference oscillator range test. I removed the
thermistor board as was suggested and checked the components for value and
location and reheated any joints that looked even a little suspect. Still
have a range of 8 Khz.
I've checked everything in the PLL area and all components are of the
correct value and where they are supposed to be. Following suit as with the
thermistor board I reheated any joints that might be considered suspect.
I did find that R110 has a low value as compared to its color code. It is
supposed to be 5.6K and it measures 3.7K. I don't think this low R110 value
would affect the PLL reference oscillator range with it being in the
variable bandwidth crystal filter circuitry.
I have to be missing something here. Ideas?
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