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You should check the waveform on each of R5, R6, R8, R9, which is equivalent to saying, across each of the capacitors
C43-C46. You are expecting to see 700Hz audio frequency signals. Yes they all have a slightly different amplitude, but
you want them to be approximately equal; and yes, the waveforms are not really nice sinewaves... just ignore that too, for
now. Just make sure that all four signals are present and look very approximately similar.
If any or all of these four QSD outputs do not have a signal, then we have to check the circuit around the QSD.
The first thing to do is to check the Clk0 and Clk1 outputs of the Si5351A Synthesiser. These have a test pin soldered in
the PCB (if you followed the assembly manual accurately). You can easily check there with an oscilloscope and should
see the 10.120MHz squarewave (for 30m; for other bands, of course it will be the selected alignment frequency for that
band). If you do not see either of Clk0 or Clk1 then you have to examine the Si5351A for any issues with soldering, such
as short-circuits, solder blobs (too much solder), poor connections (too little solder). Many of these defects will be possible
to resolve, with careful soldering.
If you see Clk0 and Clk1, but you are still missing one of these four phase outputs, or if one looks very wrong, then you
should inspect carefully the FST3253 multiplexer chip, IC4. Again inspect under a bright light and optical magnification,
look for solder bridges or other defects, as for the Si5351A. The Si5351A and the FST3253 were soldered by SMD
machines in the factory, but just like humans, even these machines are not 100% perfect.
Also check that the capacitor and resistance values are correct, and all these components are correctly installed and
soldered. I once made the mistake of soldering the four resistors where the four capacitors should go, and the four
capacitors where the four resistors should go. I have no idea why I am even admitting this in public...
