I had a similar temperature-related issue with my QMX.? It would have loud 'digital' noise for several seconds, then be perfect.? And I took it out on a POTA activation, and the noise lasted longer at startup, then was fine.? But after the sun went down and it got cold outside, the noise returned and didn't go away, and I had to qrt.
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Such noise can be caused by a cold solder joint somewhere.? So at home I took the bottom cover off, and turned it on and let it warm up to proper operation.? Then I tested it a bit by using canned air to briefly spray different parts of the bottom of the circuit card, hoping to find the location of a cold solder joint by getting it cold. [Canned air is very cold when it first comes out; at work we used to use a freeze spray for this purpose].? When I sprayed the PCM1804 chip, the noise immediately returned, and it would go away quickly if I warmed it up with a hot air gun (set to a moderately low heat).? I repeated this several times, trying to reduce the area I was cooling/heating to determine the source of the error.?? After a few tests, I could cause the noise to come with a short blast of air right on the PCM1804, and it would go away again if I touched the chip with my finger for a few seconds to warm it back up.? So in this case indeed it was the PCM1804 chip.? I replaced it, and the problem completely disappeared.
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After I replaced the chip, I realized that I never tried to just reflow the solder on it, in case one of the pins had a cold solder joint.? I should have done that, so I don't really know whether it was a failed chip or a soldering issue.? Could have been either thing.
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Stan KC7XE
