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Re: Errata: Service Manual - VCO Alignment

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  • christian.surle
    Hi Tom, I had personally noticed this error, since I had read 1.83v at TP5 on Step 2, but the rig was still going well on all bands. Glad to see that you had
    Message 1 of 2 , Feb 10, 2013
      Hi Tom,
      I had personally noticed this error, since I had read 1.83v at TP5 on Step 2, but the rig was still going well on all bands. Glad to see that you had pointed that issue 10 years before !.
      Thank you for all your contribution to the groups.
      Christian (SWL on the French Channel).

      --- In RADIOSHACKDX394@yahoogroups.com, "Tom Holden" wrote:
      >
      > I've found an error in the VCO alignment procedure on page 11 of the Service Manual. Step 2 says to adjust L14 for 21 volts at TP5 when tuned to 150 kHz. This is the same value as in Step 1 at nearly 30MHz. When I attempted this, no problem getting 21V at the high frequency but impossible at 150kHz.
      >
      > On examination of the schematic, this voltage is applied to the varactor that tunes the 1st Local Oscillator so there is no way that it is even intended to be the same voltage at two different frequencies. It should be a lower voltage for increased capacitance to oscillate at a lower frequency.
      >
      > What it should be at 150kHz, I don't know. As long as you can set 21V at 30 MHz by adjusting L14 and still have a non-zero voltage when the receiver is tuned to 150 kHz, it should be okay. If the voltage falls to zero at 150 kHz or higher, the oscillator is probably no longer phase-locked and is likely free running and unstable.
      >
      > Tom
      >
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