{Collins} KWM2 receiver front end won't resonate properly



My trusty M2 has developed a new fault over the last while. The radio was
working properly prior to this fault.
 
I have scanned the archives and have not come up with anything that
resembles my issue.

The problem is that the exciter tuning knob no longer peaks the RX signals
in the proper position. 

For example, when on 14.0, the background receiver noise will peak with the
exciter turning set to 14.0 yet the maximum signal does not occur unless the
exciter tuning knob is set to 3.4 There are several peaks as well not just
one.

I have swapped the tubes in the receive section and have cleaned the wafer
switches many times. I also ran an ohmmeter check on the wafer switches to
make sure the main wiper is making a good contact.

Among many tests, I  have injected a 14.0Mhz  100uv signal at the RX input
and have observed with a spectrum analyzer at the input into the first mixer
that the peak receive signal does occur with the exciter tuning set to 3.4
not 14.0.  This problem occurs on all bands.

The S meter also peaks at the incorrect setting of the exiting tuning knob 
on all bands.

Using a tunnel dipper, I tried to check the resonance of the various slug
tuned coils but the tunnel dipper does not have enough coupling to give a
dip.

I verified that the band oscillator crystals are on the correct frequency.

The only thing I can think of is perhaps one of slug tuned coils is open or
some wire to a cap has broken?

I am troubleshooting with the four bottom shields off so perhaps that is
causing problems?
 
Any suggestions would be greatly appreciated as I am exhausting my limited
knowledge in repairing this radio.

73, Bernie
VE3FWF, Ottawa, Canada

 





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