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?PART: PCM1804DB-ND
MFG : TEXAS INSTRUMENTS / PCM1804DB
DESC: IC ADC/AUDIO 24BIT 192K 28SSOP 5.76000 23.04
COO : JAPAN ECCN: EAR99 HTSUS: 8542.39.0030
ROHS3 COMP REACH UNAFFECTED 10-JUN-2022
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73
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Ian G4GIR
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----- Original Message -----
Sent: 30/01/2025 19:27:46
Subject: Re: [QRPLabs] QMX+ with ~1000 tone on 12M & 6M
Question to Mike, KK7ER:
What is the DigiKey p/n for the PCM1804?
Larry K3PEG
On Wed, Jan 29, 2025 at 07:56 AM, Richard Hattaway wrote:
the tone is there if I have the computer attached via USB or not Same here, Dick.
I even took the rig outside just to be sure I was not picking up something in the house.
The new PCM1804 just arrived from Digikey.
Hopefully, this one will go more smoothly than that (where I ended up lifting a PCB trace in the process)!
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73, Mike KK7ER
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Thanks, Ian.
73,
Larry K3PEG
?PART: PCM1804DB-ND
MFG : TEXAS INSTRUMENTS / PCM1804DB
DESC: IC ADC/AUDIO 24BIT 192K 28SSOP 5.76000 23.04
COO : JAPAN ECCN: EAR99 HTSUS: 8542.39.0030
ROHS3 COMP REACH UNAFFECTED 10-JUN-2022
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73
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Ian G4GIR
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----- Original Message -----
Sent: 30/01/2025 19:27:46
Subject: Re: [QRPLabs] QMX+ with ~1000 tone on 12M & 6M
Question to Mike, KK7ER:
What is the DigiKey p/n for the PCM1804?
Larry K3PEG
On Wed, Jan 29, 2025 at 07:56 AM, Richard Hattaway wrote:
the tone is there if I have the computer attached via USB or not Same here, Dick.
I even took the rig outside just to be sure I was not picking up something in the house.
The new PCM1804 just arrived from Digikey.
Hopefully, this one will go more smoothly than that (where I ended up lifting a PCB trace in the process)!
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73, Mike KK7ER
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On Thu, Jan 30, 2025 at 11:28 AM, Larry Przyborowski wrote:
Question to Mike, KK7ER:
What is the DigiKey p/n for the PCM1804?
The one I ordered is:
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PCM1804DBR
296-26306-1-ND
IC ADC/AUDIO 24BIT 192K 28SSOP
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But I think Ian's part number is equivalent.
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73, Mike KK7ER
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Thanks, Mike.
73, Larry K3PEG
On Thu, Jan 30, 2025 at 11:28 AM, Larry Przyborowski wrote:
Question to Mike, KK7ER:
What is the DigiKey p/n for the PCM1804?
The one I ordered is:
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PCM1804DBR
296-26306-1-ND
IC ADC/AUDIO 24BIT 192K 28SSOP
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But I think Ian's part number is equivalent.
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73, Mike KK7ER
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Today I got some time to play with the QMX+.? As stated earlier it had the tone on 12 and 6, and in the process of trying to fine tune some toroids, it suddenly quit RX all together.? There was a pop in the headphones ( I speculate ) when it stopped.
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l found that the expected 2.5 volts across C406 was not there.? It was 11mV telling me either C406 is shorted or IC 402 pin 7 is pulling the voltage down, or same for IC403 pin 7 and or 9.? I dont know the likelihood of a shorted SMD capacitor.? But it's the easiest to test.? Then of course lift legs on the IC's.
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I post this here because the receiver sounds great.? The filters work, Digi to CW mode change sounds just like it should in the headphones, etc etc.? Just no signals present.??
The 'odd' thing is that there is no 1000 HZ tone on 12 or 6 M .? So maybe the origination of the tone is somewhere else behind the suspect PCM1804 ??? Since I have no serious understanding of the operation of this circuit, I cannot speculate on where this tone is coming from.??
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More to follow.
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73
Dick
W4PID
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You say:
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It does not change in level or tone while tuning around the band.
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Does that not eliminate RF subsystems entirely as the source? It seems to me this would confine it to the audio subsystems.
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73;
Bob KV4PC?
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Bob,?
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interesting diagnosis. I’m an old guy, and if it were a superhet from my era then I would agree 100 %.?
I don’t understand the new designs in RX and all the magic happening in little fingernail sized pieces of plastic. ?I can’t even define where the RF subsystem and the audio subsystem meet. ?I need to do a lot more reading.?
The tone I am concerned with is precisely 1000 Hz per the FT8 software. I think it’s the same for others who have reported the issue. The RX still worked at that point but the tone made copying CW difficult. The precise nature of this tone leads me to believe it’s related to a signal generated by an oscillator or computer chip. Beyond that I am flying blind, so I must read more.?
As I pondered the tone, ?the RX went deaf with a pop in the headphones while I was using putty to observe the results of pushing turns around on the 160 M filter. So I have to solve that issue first then return to the tone, assuming it will still be there after I get 2.5 V on the ungrounded end of C406.?
Thanks for the input and stay tuned. More to come?
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73
Dick
W4PID
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Dick,
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Were you pushing the turns around on the toroid with the board in the case? If so, I wonder if the board flexed enough to short something on the underside of the board to the case. Or maybe flexed a solder joint or smd connection.
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Regards.
Rowan.
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Mine has the 1kHz tone. Originally it was audible on all bands but strong on 24MHz and 50MHz,
I changed the PCM1804 and it’s only on 24 and 50, lower level than before, but still there.
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QMX+ rev.3 9v build.
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I would also like to report the same anomaly observed on 17m and 6m.
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I was 'playing' around with the CW filter and decided to try out the 'none' option, disabling the filter. I started tuning around and all seems ok, I could listen to SSB etc..
I hopped on to the 6m and was met with a very high level of noise. I can confirm that the noise I heard was as described by all on this thread. I can also confirm the CW like clicking noise, short and long random clicks. The noise was all accros the 6m band with filter switched off. The level and noise content did not change.?
I then started hopping around bands to see if I can hear it on other bands. I also found it on 17m.
I shorted out the antenna to isolate any external interference, the noise level and characteristics didn't change.
I went back into the menu and renabled the filter. With the filter now engaged, the noise almost completely disappears, but still could hear the CW like clicking and the 1k tone very faintly.
The noise is generated internally, I'm quite certain of it.?
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Mel. M0KMD
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Further to me report of the same issue, I just did a factory reset and the 1khz constant tone is quite prominent on 6m.
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Mel. M0KMD
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Rowan (and group)
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A report on progress here.? A bit of catch up history..?
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My QMX+ was reported with a 1000 hz tone with some kind of faint digital signal modulation on 12 and 6 Meters.? It was also seen on 10M but not nearly as loud.? Reported initially, the signal was isolated to be within the RX.? Several other members reported the very same or similar symptoms.? The TX works great.
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In the process of poking around the RX areas trying to change LP filter plots, I killed the entire RX.? This turned out to be IC402 and when replaced, the RX came back to life.?
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I noticed that there was NO 1000 Hz tones in the audio output when IC402 was dead.? There were no signals either, but the filter 'sounds' of narrow CW seemed to work fine.? It sounded just like the RX should, but no signals.? Once IC402 was replaced, the tones on 12 and 6 meters are back. as well as the expected signals.??
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I replaced the PMS1804 chip. MANY THANKS to Jeff Moore and others who have plowed this ground before me.? It was a relatively painless experience.? Briefly if you have the 10$ ChipQuik kit, some solder wick, and the iron you built the kit with, you too can change this very intimidating chip.? This did not cure the 1000 Hz tone.? I believe Jeff has seen this happen too.??
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So I have gone around the block, learned new skills but I have not solved the original problem.
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I am on the verge of ordering a front end chip ( the first RF stage in the RX ) because the tone disappeared when I cut that chip off from the rest of the radio by killing the IC402.
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I am open to ideas.??
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73
Dick
W4PID
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PS Rowan, I did notice some tabs on the bottom of the board to be perilously close to the case.? I trimmed these and no more threat exists there.? Thanks for the heads up.? It may or may not have been the issue, as I was only scooting turns around on the 160M RX filter toroid when the failure occurred.? But it did cause me to pull the board and trim, maybe averting some issue down the road.
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well? just to report, that my QMX+ has that tone also on 12m,, 10 m and 6 m . I have an assembled one on order and will be curious to see if that has that noise too.
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Martin
DK3UW
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As I was reading through this thread, I remembered a video Hans did on tracing an audio signal using a cheap handheld digital oscilloscope. I have one of these little $30 pocket scopes and have used it this way a few times. This may help you trace and narrow down the issue:
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73, Dan - W2DLC
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I just received my factory build QMX+ and it does have the same tone as the QMX + I had built.? So can it be something within the QMX concept ? I noticed that the volume of the tone is not always identical but I could not fugure out a rule for that.
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Apart from that, I find the CW tone quite rough ( not the sidetone)
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Martin
DK3UW
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just tried the QMX+ on 6 m and I must say thast it is not really usable there. I had the pleasant surprise that there was Tz4AM? announced on RBN and I had him 599 with my Flex 1500 and the DK7ZB single diamond shaped loop. And I did work him and got 339. On the QMX the signal was much lower and not much above the 1000 hz or so constant tone.
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Martin
DK3UW
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PS I try to attack a Video hoping it passes
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Martin, if you use a simple set of earbuds to listen to the QMX+ rather than your external speaker, is the tone any different??
Also, if you listen to the audio via the USB port connection and your computer, does the tone still appear?
One user recently wrote that he got rid of the tone by using a different speaker, so I'm wondering if it is somehow an oscillation problem in the audio circuitry.? Listening via the USB port into a computer (like using digi mode) would separate it from the audio output hardware - if it is still there in the same way, it is further forward in the receive path.
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Neither of my 2 QMX+ nor 2 QMX have this issue, so I'm curious as to what could cause it for some of you.
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And I apologize if this question has already been discussed, I didn't read all of the prior entries on this thread.
Stan KC7XE
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Hi Stan,?
in my case the tone is there in 6 and 12M and present but not totally horrible on 10M. It is visible as a 1000 Hz signal on WSJT software. ?It appears to be very consistent at 1000 Hz making me think it’s computer generated.?
As Martin reported it is so strong on 6 and 12 as to make the radio useless on those bands.?
I have replaced the PCM1804 chip with no change. This is the same for several other folks. I also replaced IC402 due to other issues and the tone remained.?
Martins report is the first one I have seen that was on a factory unit.?
I will continue to experiment as I get time but the next two weeks are busy here.?
73
Dick
W4PID
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Richard Hattaway
Bob KV4PC
Daniel Conklin