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I feel like I remember this coming up before but can't for the life of me find the previous topic. About half the time when I boot up my QMX rev1 (1_00_027) I get this faint, rapid clicking noise that's going at maybe 10 clicks per sec and no other sound from the radio. And then another 5% of the time it's just silence. And then another 5% of the time it's this incredibly loud sound that I finally got a recording of (attached). I've tried turning the AGC on and off, going into digital mode and back, and nothing seems to fix any of the problems other than shutting it down and booting it back up. Once I boot it up and everything sounds normal the radio works great, though on a rare occasion I will randomly get that really loud noise from spinning the tune knob (might not be correlated but it's never happened just listening to a freq with no interaction).

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Guessing it has to do with IC401 (CS4334) and I need to replace it, but just wanted to confirm with y'all in case there's something simpler I can do.

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Brad W8BMO

Sounds like this:

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I have a QMX with the batch of bad PCM1804's. So far, I just need to warm up the QMX before using it to get rid of the noise.

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73,

Steve, N2IC

Ahh, interesting. I'll try some of those diagnostics to see if I can verify mine is the PCM1804 and report back.

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Thanks, Steve!

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Brad W8BMO

I also have this incredibly loud noise on startup from time to time. I have found that if I just turn the audio volume down it is fine. It's as if the software "forgets" the audio setting sometimes, and sets it to max.

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Sverre

I have that exact same noise as well, maybe about 10% of the time.? In my case I can power off / on again and all is well.? My unit also dates back to the questionable batch of PCM1804 ICs so I have acquired some new ICs from Mouser.? As it stands now I'm just living with the issue since it doesn't happen that often.? If it starts being more bothersome then I will do the replacement.

Somehow I missed the notice/discussion about flaky PCM1804 chips. But my high band QMX will sometimes “freak out” with the same noise in the audio recording above, at ear splitting volume. In fact, I don’t use headphones with that radio for fear of more hearing damage.

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But can I replace the PCM1804 for a reliable fix?

On Mon, Mar 17, 2025 at 07:05 AM, Matt - W6CSN wrote:

can I replace the PCM1804 for a reliable fix?

IF the PCM1804 is the source of the problem,? then yes, replacing it with a genuine part will fix the problem.? ?I had one that was temperature-dependent.? ?It would give the loud digital noise until the QMX warmed up a bit, then was fine. Or when I was operating outside and it got cold at night, the noise would come back.? Replacing the chip completely cured the issue.

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But there is another potential source for your issue.? ?The D/A chip on the audio output (CS4334) gets initialized only at power-up of the QMX.? If something causes that initialization to fail, it can give a bad noisy output.? ?This can happen if the chip is bad (has poor timing response to the setup), or there is noise on the processor lines for whatever reason (bad solder joint somewhere, rfi, power supply issues, other unknowns).? If that is the case, re-soldering or replacing that chip may fix the problem.?

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Stan KC7XE?

Messed around with it a little bit by putting it in the fridge to get the temp down. The surface of PCM1804 was showing a temp of 60F and about 1/3 of the time on boot-up it would either be silent, clicking, or the loud noise. Got through about 20 boot-ups before the chip temp was showing around 73F and then I tried about 20 more boot-ups without any failures. Put it back in the fridge and on the second round I was just trying to see if the loud noise would go away if I warmed the chip up; got the loud noise and pointed a 200F hot air gun at the chip and it never quieted down. Makes sense that if it's just a volume issue though that it would persist regardless of the temp. I guess having a better understanding of what's happening I'm kind of okay with it -- same as Jim, I'm not sure if it's worth replacing at the moment since it's operating perfectly once it gets through a proper boot. I already had to replace IC503 and I'm not super eager to replace a chip with a ton of other SMD components right next to it. Will probably order a PCM1804 and the CS4334 just to have on hand in case I'm feeling adventurous one day, but right now it's my only rig and I don't want to accidentally brick it. :D If the issue ever comes back where the loud noise manifests during the middle of operating the rig, I'll definitely replace something because I'm pretty sure that's gonna damage my hearing.

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Appreciate all the input!

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Brad W8BMO

FWIW, I’ve only experienced “the noise” after operating for some, inconsistent, time. But, never had the issue appear when booting up the radio.

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Probably I will not worry about it, I have the mid-band QMX built and never had an issue with it.

My high band QMX demonstrated this loud harsh noise on boot up that would diminish as the unit got warmer.?

A new TI PCM1804 cured the issue completely.?

73

Dick

W4PID?