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My QMX + kit was working well for some weeks -- until two days ago, when a power-on yielded mute audio.
Several on and off cycles seemed to fix it, and I blissfully (and foolishly)? presumed it was just a passing anomaly.
But the symptoms arose a few more times and a search of the forums produced a flood of queries, which kept pointing at a flawed PCM1804, the IC that controls audio.
The malfunctions continued off and on without warning.
Research reveals that Texas Instruments is aware of its failure rates and no longer recommends using it. TI has replaced it with another IC.
Thus the dilemma -- what's the point of replacing a faulty PCM1804 if even its manufacturer has no confidence in it??
I love this rig (when it's working), but I don't plan on using it on POTA or other portable ops until this intermittent, unpredictable failure is resolved and I can depend on it.
In addition to no audio, the glitch also presents a very loud blast of sound that defies description.
I attach a brief video with sound here to demonstrate its characteristics.
What is the current best thinking and practice on how to deal with this ?
Are there any plans to replace the PCM1804 in a redesign of the QMX+ ?
Thanks for indulging me. 73.
- Bill W3WJ
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Hi Bill,
Please describe the voltage of your QMX+, the type power supply, etc.
Also a pix of the board in the area of
PCM 1804 if you would. Sorry you are having the difficulty.
73,
George?
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Hi George.
It's built for 12V? The power supply is a Bioenno 12V 12AH down-regulated with a DROC to a measured 12V.
- Bill
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George, here's the board in the vicinity of the 1804.
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Hi Bill,?
I use a DROK, in fact 15 of them,
and we are on the same page. I use them with 20 volt batteries. I did make a switch with QMX+ to a DROK 12 v. regulator because the DROK buck converters, sometimes have trouble with big interconnected ground planes. This trouble can be intermittent. QMX+ is a different beast in terms of PCB and grounds, and the power plug routes, so to be safe, I upgraded to the DROK regulator. It's kind of chunky compared to the small DROK but much more isolated.?
George
PS I can send a link if you need it.
May not solve this current problem,
but faster than waiting for a rev.PCB
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I don't see anything in the pix, but there are plenty of reports of flaky SMD solder joints. Hans will sort this out, he always does.
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George, here is the converter that I use.??
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- Bill
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Well we are in the same page!
Wait for Hans... The chances of a bad component are slim but I deter to your investigate skills, sir. Hans is really good with ' shit happrns'?
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BTW, your Art Site is wonderful.?
I gotta look again and shop!
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Thank you very much, George.? I hope you enjoy the photo art.?
- Bill?
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Hi Bill,
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could you please provide some reference for your statement "Research reveals that Texas Instruments is aware of its failure rates and no longer recommends using it".
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All I can find at TI is that this device, introduced in 2001 (more than 20 years ago), has higher performance successors in modern, tiny, "not replaceable by hobbyist "-packages.
This seems to be normal procedure to me.
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KR
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Dirk
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DK7CVD
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Dirk, this is from the TI site ... it shows the company is not recommending it for new projects.? Note the very last sentence. To me, that reads as a no-confidence vote going forward.
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112dB SNR Stereo ADC With Differential Inputs
A newer version of this product is available
This product continues to be available for existing customers. New designs should consider an alternate product.
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Hi Bill,
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sorry, but I have to disagree.
This is the usual first step of phasing out of old designs.
Consider new product -> not recommended for new design -> obsolete -> not available anymore
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As mentioned before, this is an 20 year old design and the majority of today's products will use the tiny 4x4 mm package of the TAA5442.
"Bulky" SSOP is not up to date anymore, there is no indication of a general technical issue.
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KR
Dirk
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I agree with Dirk¡¯s assessment. Twenty years is a long time for a semiconductor to be on the market so TI is gently pushing customers toward newer devices. I found no reliable reports of the PCM1804 having known defects but it is an old Burr Brown device and, as such, TI is replacing it with newer, more power-efficient designs. The average life of a semiconductor is roughly ten years in today¡¯s market. PCM1820 seems to be the eventual replacement.
Tony AC9QY
Hi Bill,
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sorry, but I have to disagree.
This is the usual first step of phasing out of old designs.
Consider new product -> not recommended for new design -> obsolete -> not available anymore
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As mentioned before, this is an 20 year old design and the majority of today's products will use the tiny 4x4 mm package of the TAA5442.
"Bulky" SSOP is not up to date anymore, there is no indication of a general technical issue.
?
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KR
Dirk
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Who knows TI's precise motivation for replacing the PCM1804?? It wasn't their product in the first place, but a tagalong in the B&B merger. Admittedly 20 years seems a long time, but as a wise mentor here has said, "If it ain't broke, don't fix it.'? ?If the function is there, the form factor may or may not be relevant, depending on the application.?
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If there are no signs of a 'general technical issue,' then to what do we attribute the number of PCM1804 failures reported on this forum as well as elsewhere??
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My QMX + has the same varied audio glitches as reported in detail by a number of forum participants.? Expert repair members here have replaced the PCM1804 and resolved the problems.?
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Back to my original? reason to post:? Is it worth replacing the IC, as its reliability is in question???
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I paid for this kit, successfully built and operated it. Then one day after several weeks, it powered on with either dead audio, or the blast of an end-times sound that made the 700hz test tone compare as a kitten's whisper. To hear the noise, listen to the video I originally posted.?
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It's a super rig; one that I'd like to rely on functioning.??
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I'm hoping one of the experienced repair experts will comment.
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Bill? W3WJ
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Bill,
TI is still shipping Burr Brown devices. They¡¯re excellent performers but BB devices are power hogs. As with all semiconductor vendors, to remain competitive, TI must move to smaller technologies to improve yields. It eventually becomes cost-prohibitive to maintain outdated semiconductor fab lines so they redesign for smaller device technologies on modern fab lines. If it was only a matter of outdated packaging, they would offer these devices in newer packages rather than replacing them. The semi industry is heavily driven by cost/profit/usage analysis so popular chips will be shrunk for the latest fab lines and less popular ones are simply obsoleted. It ain¡¯t broke for customers but it ain¡¯t cost-effective for TI.
Tony
Who knows TI's precise motivation for replacing the PCM1804?? It wasn't their product in the first place, but a tagalong in the B&B merger. Admittedly 20 years seems a long time, but as a wise mentor here has said, "If it ain't broke, don't fix it.'? ?If the function is there, the form factor may or may not be relevant, depending on the application.?
?
If there are no signs of a 'general technical issue,' then to what do we attribute the number of PCM1804 failures reported on this forum as well as elsewhere??
?
My QMX + has the same varied audio glitches as reported in detail by a number of forum participants.? Expert repair members here have replaced the PCM1804 and resolved the problems.?
?
Back to my original? reason to post:? Is it worth replacing the IC, as its reliability is in question???
?
I paid for this kit, successfully built and operated it. Then one day after several weeks, it powered on with either dead audio, or the blast of an end-times sound that made the 700hz test tone compare as a kitten's whisper. To hear the noise, listen to the video I originally posted.?
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It's a super rig; one that I'd like to rely on functioning.??
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I'm hoping one of the experienced repair experts will comment.
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Bill? W3WJ
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Hi Bill,
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lets move towards your initial question. My QMX came with an DOA PCM1804 and I succesfully replaced it. Since then the QMX works fine.
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The PCM decodes the RF input via the I-Q-something, it's not generating the audio.
I had random noise and always a high S meter readings, there was never silence.? So maybe the PCM1804 is not the issue.
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Have you checked the device via USB and WSJT if you have reception?
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73
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Dirk ? DK7CVD
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I hadn't used my mid-band QMX since the 14th. It was turned off with the antenna disconnected.
When I powered it on this morning, I had muted audio as well, with a slight motorboating sound.. Adjusting the audio gain didn't seem to affect the volume. I swapped out the SoundCore Mini for earbuds, but no change. I did a factory reset and everything seems to be A-Ok again. Worked a POTA station on 14059kHz...
gl de va3rr
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On Tue, Aug 20, 2024 at 12:38 PM, Bill Jobes wrote: I paid for this kit, successfully built and operated it. Then one day after
several weeks, it powered on with either dead audio
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Dirk
va3rr