And if you see the signals as described, either you have a PCM1804 failure, or you have a failure in your audio output path.
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To determine which of these, consider the following observations: do you get receive audio via the USB computer interface path?? e.g. receive ft8 data in wsjt-x, or see signals with IQ mode enabled in an sdr program like NaP3 or HDSDR?? If you get audio via this path, the PCM1804 is fine, and the fault lies in the audio-out circuits.
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Note that complex ICs do have a non-zero failure rate (even the good ones), so while it is much less likely on an R4 board to have a failure in the PCM1804 or one of the audio-out chips, it can happen.
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Good luck in finding the culprit,? and let us know what you find next.
