It is helpful to determine which stage is causing the problem. It will be
either the mixer, the oscillator or the rf amplifier. Some stages use 2
decks. See if you can hear the oscillator in another receiver. It is 455
kHz away from the tuned frequency, and you can hear it on a nearby receiver.

It could be a component so do not tear apart the bandswitch without
confirming that is really the problem. More than once I have spent time
servicing the wrong problem because I did not do a good job of diagnosis.

Fortunately, the penalty occasional incompetence is less than if the surgeon
removes the wrong part.

A signal generator can be used, too. Inject a signal (through a cap) into
the mixer, to replace a missing oscillator signal (remember 455 kHz away).
If no improvement, try injecting a signal into the mixer at the grid.

A little square wave oscillator with harmonics all over the place can give
you a quick diagnosis by putting it on the various grids of the mixer.

After enough projects like this, you will be answering questions, too.

Colin K7FM


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