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My audio sweep on a newly built (by me) QMX is showing levels of around -22dB as the max value. The wiki for the PCM1804 (/g/QRPLabs/wiki/37111)? says there is a problem if the audio levels are "very?low level from audio sweep". Does anyone know whether the levels I am seeing count as "Very low" or not? IF they count as low, I don't think it is a PCM1804 issue, more to do with the path through C509 as I can see a signal on one side of C509 but not the other. I have disconnected L401 but the signal doesn't appear on C509 so it isn't that, and I can't see or measure any shorts anywhere. However I don't know whether I am chasing a none-existent problem. Thanks,
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Steve M7WGN. |
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I took the QMX to work to use their? high power binocular microscopes and found that the end pad of C509 looked like it had a crack in it. I replaced the cap and everything now looks like the pictures in the operating manual. I couldn't see any cutter scrapes or other physical contact damage on the capacitor, so I don't know whether this was an unlucky build fault or my self inflicted damage, but my suspicion is that I must have done it somehow as the rest of the surface mount build looks good and I don't believe I had a bad cap and no-one else has.
As to my original question - does a reading of -26dB on the audio scan count as "Very-low" , then I think it does. If you get low values (-20dB? -26dB) on most of the scans in the Hardware tests, then it is worth following the path through C509 to see if there is any damage.
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Steve.
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va3rr