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Now we can check at the top end of the long winding of the T1 transformer. Since this long winding and the trimmer
capacitor act as a band pass filter, you can see that we see a nice sinewave now. This is labelled "1" in the diagrams
above. It is the point shown by the arrow, in this photograph:
Note that the amplitude of the sinewave seen at this resonant tank circuit does change when you adjust trimmer capacitor
C1. Try it, just to prove it and to check. This is not an accurate way to adjust the band pass filter, because the 'scope
probe itself also loads the resonant circuit. So it is not a substitute for using the configuration menu item. But it's nice to
see that the theory holds true in practice. And it also verifies that the BPF circuit is working properly - which is what this
fault-finding is all about, after all.
If you can't adjust the amplitude with the trimmer capacitor, then check that the trimmer capacitor is correctly installed and
soldered; and check that it was not broken during the installation; or the delicate plastic melted by over-heating.
