It sounds like either your synthesizer is out of lock or the bandswitching
diodes in the front end aren't being switched by the microcontroller. You
probably have some sort of current booster chip such as a ULNXXXX or some
switching transistors that switch the receiver above the 1.6MHz range. Since
you are hearing different levels of white noise, I believe that your
synthesizer is ok. You can determine that by connecting a frequency counter
to your 1st LO injection point. If everything in this section of the circuit
is ok, you will see a frequency that is above your actual displayed
frequency by whatever the 1st intermediate frequency is. The key is that
when you change your tuning frequency by 1MHz for instance, your 1st LO
frequency will change by that amount.
I don't know if that receiver uses relay or diode switching to switch
different ranges of the preselector when you tune the shortwave bands. You
could actually bypass the preselector and connect an antenna wire directly
to the low-pass filter that is ahead of your 1st mixer. On a final
note.............................is there a switch on the back panel of the
7700 that selects between long wire and 50 Ohm inputs? If so, that could be
the cause. Either that switch is set to the wrong position or it is dirty.
Good luck!

Pete

"saki" wrote in message
...
Jon Doe wrote:

Try using some spray tuner cleaner on the backside of the
bandswitch.. Looks like it may not be functioning.

I'll do that, though it appears that the bandswitch is working okay. At
least when I change bands the frequency readout changes too and I hear
different levels of white noise.

Thanks for the suggestion!

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