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Well said, Allison, excellent reminder!? Very similar to my experience.
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I definitely would encourage using good ESD practices during handling and assembly of QRP-Labs kits, including use of a good ESD mat and wrist strap.? It would likely significantly decrease failures that happen for "unkown reasons", sometimes after the assembled kit has been working and in use for a time.?
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Invisible ESD events can weaken a chip internally such that it later fails during normal operation.?
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Stan KC7XE?
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My experience with assembled board (and repaird boards) at a really larger computer
manufacturer is all ESD.
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Example board fails or deemed failed (board swapping) returned ot Depot to test and repair.
Tested board is repackaged and eventually to the field for use.... only to be returned again
now failed.? With thousands of said boards repair costs were a factor so investigation found
ESD (we are talking 74xxxx class TTL)? was the cause.? Adding tracking to the system? found
where and even who so inquiry was done to find out.??
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End result was ESD at the site end point, in dry locations, and Field Engineer not using?
ESD handling technique.? Or the external system had poor grounding and introducing?
transients (traceable to board that did external interfacing to the machines.? Generally
reinforcing ESD procedure in the field and insuring they had needed kit had a marked?
improvement in dead on arrival (or shortly after) boards.
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Likely cause would be during last parts stuffing (end user) the board suffered ESD hits
likely un-noticed while handling.? So that might answer shipped good failed in field.
Those would not be guarenteed immune as its cmos in a cmos environment unpowered.
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Also that would be seasonal, aka worse in dry weather (desert southwest usa)?
or during winter (heated dry air).
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I'd add ESD warning during assembly with suggesting mats and all.
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Allison
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Post online only,?
direct email will go to a bit bucket.
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Further continuity testing shows a break between C423 and the junction of IC405B pin 6, R413 and R417.
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I venture to write this would be enough to render IC407 with no signal to process.
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73
Karl
KI4ZUQ
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So I am preparing to inject a signal and see the path through IC405 and IC406 makes it to IC407, the PCM1804 and what do I find? A complete continuity break from C422 to the junction of IC405, R413 and R416!
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73
Karl
KI4ZUQ
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On Sun, Mar 16, 2025 at 10:31 PM, Karl wrote:
would see about 2.5 vdc on certain bands
Karl, I guess you mean IC402 and IC403 and for QMX+ IC408. If one or more is/ are broken it will interrupt the RX signal path.
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A good way to check if the problem is inside the PCM1804 or before this IC is using the method No 2 from QMX QMX_plus Audio PCM1804 section Diagnostics. ?
73 Ludwig
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Thanks, Ludwig! Appreciate your input!
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Somewhere? on this forum and on this topic of PCM1804 failures is a voltage check on pin pairs of the 1804. I saw it, read it and thought I could find it...but...
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I think it was different? pairs would see about 2.5 vdc on certain bands..where was that? I will delay replacing the IC407/PCM1804 until this simple test is passed.
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By the way, my 1804 looks like authentic Texas Instruments logo but then a fake would, too.
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73
Karl
KI4ZUQ
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Karl, Audio, RF, image and Test ADC I/Q sweeps on the one hand and LPF sweep on the other hand? are using different ways. After reading QMX Terminal Hardware Sweeps you may have a clue where to debug. Maybe it's a broken PCM1804 (see QMX QMX_plus Audio PCM1804 ) or a failure in the section from Q508 up to IC407 (PCM1804). ?
73 Ludwig
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So maybe I have an IC407/PCM1804 failure on a QMX+ REV1 board? Audio, RF, image and Test ADC I/Q sweeps are all static, random noise plots while LPF is better than any of the three or four QRP Labs transceivers I have built yet. SWR is kinda okay and receive is loud noise.
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What say you? I will try the voltage and mayne the scope checks...
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73
Karl
KI4ZUQ
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I am, in all likelihood, one of those hit by the? PCM1804 problem.? I have read threads about replacing it
and bought replacement chips and the necessary tools, but I doubt my eyesight and? dexterity are equal to the task.
Wrecking my QMX is the most likely outcome.
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I would rather restart the build with a PCB known to contain a good PCM1804. Buying a new QMX (which would be my third,
since my first was accidentally destroyed) is expensive. If replacement PCBs (just the part containing the PCM1804) were
available, I would buy one, reusing the SMPS, front panel, and all salvageable components.
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I think Hans could consider making such replacement PCBs available at or near cost to previous buyers of a QMX,
on a one-for-one basis. I also? feel warning should be given to prospective builders that there is (aparently) a 15%
chance of having to replace a SMD component, something which is at the boundary or beyond of what many of us
can tackle.
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I have no idea what procedures QRP Labs has before shipping a QMX+,? so take this with as much skepticism as you can muster:
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My assumption is that they plug in a USB cable to program the STM32F and power the board up, not much more.
That USB cable is just a connection to ground and a couple pins on the STM32F, nothing anywhere near the PCM1804 gets touched.
A fake received signal would have to be driven into pins 7 and 9 of IC403, but that is well isolated from the PCM1804.
The power supplies on the QMX+ are complete, exactly as they will be when shipped to the customer.
I can't imagine any reason for the procedure to physically disturb the PCM1804 in a way that would not happen after a bad chip is replaced.
Any handling at QRP Labs would likely be considerably more benign than that of the typical kit builder who is adding dozens of parts.
My understanding is that the PCM1804 seldom (never?) fails once the PCM1804 has been found to work, either during initial testing at QRP Labs
for recent versions of the QDX and QMX+,? or after Jeff has replaced a PCM1804 (which I'd guess is now mostly on the QMX, since
the QDX and QMX+ have already been tested).? Older kits that did not have firmware loaded at QRP Labs don't have the PCM1804 tested.
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If the above is correct, it sounds to me llke the assembly house is stuffing bad parts.
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I could easily imagine that shorting the VCC rail (perhaps due to clearance issues around the front panel) would cause a spike in VCC when the short is removed, blowing the PCM1804.? However, if such failures seldom (never?) occur after the receiver has been found to be working correctly,?
that is probably not an issue.
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A complete bed of nails would not be required to test the PCM1804 on the currently untested QMX.? I would think it would just require applying VCC and VDD, a USB cable to a host computer that has appropriate test software, and appropriate signals at IC403 pins 7 and 9 that are 180 degrees out of phase.??
Getting this working properly could take several days that Hans does not have, but should not take weeks and a major hardware effort.
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Jerry, KE7ER
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On Fri, Jan 3, 2025 at 05:42 AM, Bruce Akhurst wrote:
I suspect ESD or power supply damage to an incomplete board would not be repeated once fully built.? ESD damage, to ICs in particular, is often evident only after a few weeks or months...
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I suspect ESD or power supply damage to an incomplete board would not be repeated once fully built.? ESD damage, to ICs in particular, is often evident only after a few weeks or months...
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On Wed, Jan 1, 2025 at 11:22 AM, Hans Summers wrote:
QMX is the outstanding problem. We will find a solution to that too.?
The QMX boards could be tested with some sort of bed of nails test fixture that provided the appropriate test signals for IC403 couldn't they?
Use the CLK2 signal attenuated by R513 with a suitable level and phase shift, then the Rx Audio and Image tests should work.? That's enough to test most of the Rx side on an unpopulated board.
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Yeah like my QCX-mini test fixture:
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Yes, that's the sort of thing I was thinking of, not surprised you have already tried it..
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I understand that it's a lot of work to make but if 1 in 7 of the QMX kits fail because of the PCM1804 problem 100% testing seems essential.? I don't think it's reasonable to keep shipping QMXs untested if that level of failure can be expected, it isn't fair on your customers.
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Would a test rig that picked up the test signal from R518 and passed it through T401 to the inputs of IC403 work?? Your test harness would provide VCC and VDD and ground, that's 6 or 7 pins.? Run the Rx diagnostics through the USB connection.? This bypasses the LPFs and the BPFs but if they are needed they could be added to the test rig and a single band test done.? The alternative seems to be to connect each board manually using test clips, time consuming and error prone.
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Chris, G5CTH
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If boards with a failed PCM1804 never fail when the part is replaced, that points to counterfeit parts.?
No, it doesn't; counterfeit parts is only one option; there could also be ESD problems causing it, either during assembly, or subsequent handling somewhere along the line; or there could be problems during our bootloader flashing and testing procedures.? ? And I'd not have them stuffed at that assembly house, make it?a hand add at QRP Labs instead.
Just when I thought I was already having the maximum amount of fun possible per day...
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Jeff Moore has never seen a PCM1804 fail after he’s replaced it and he replaces quite a few of them. Jeff is sourcing replacement devices from Digikey and they’re also available directly from TI.com. I tend to agree there’s something amiss in the CM’s procurement process.
Tony
If boards with a failed PCM1804 never fail when the part is replaced, that points to counterfeit parts.? And I'd not have them stuffed at that assembly house, make it?a hand add at QRP Labs instead.
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Jerry, KE7ER
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On Thu, Jan 2, 2025 at 07:56 AM, Jerry Gaffke wrote:
When final test detects a problem with the PCM1804, do they replace it with stock you buy from directly from TI?
Do these parts also fail in the same way at a 15% rate?
It could be your assembly house is sourcing what they believe are parts from TI, but they are counterfeit.
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If boards with a failed PCM1804 never fail when the part is replaced, that points to counterfeit parts.? And I'd not have them stuffed at that assembly house, make it?a hand add at QRP Labs instead.
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Jerry, KE7ER
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On Thu, Jan 2, 2025 at 07:56 AM, Jerry Gaffke wrote:
When final test detects a problem with the PCM1804, do they replace it with stock you buy from directly from TI?
Do these parts also fail in the same way at a 15% rate?
It could be your assembly house is sourcing what they believe are parts from TI, but they are counterfeit.
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Hans,
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Looking at web hits for PCM1804 failures other than on QM* products, I only see low level noise issues.
What's being reported in this forum is complete failure.
A 15% failure rate is nuts.
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When final test detects a problem with the PCM1804, do they replace it with stock you buy from directly from TI?
Do these parts also fail in the same way at a 15% rate?
It could be your assembly house is sourcing what they believe are parts from TI, but they are counterfeit.
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Have you looked at the PCM4202?
Claims to be pin and function compatible with the PCM1804, $3.20 US direct from TI at 1K quantity.
From the dates in the datasheet, it came out a couple years after the PCM1804.
Being almost identical, it makes me wonder why they bothered to do this.
Page 23 of the datasheet shows differences between the two parts, none of which look like a problem.
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The PCM1804 and PCM4202 are both over two decades old, TI has the much newer
PCM1820 and TAA5242 parts that might be considered for future QRP Labs products.
Those are very small with a 0.5mm pin pitch and a center ground pad, much harder to work with.
But perfect for a possible QMXnano, to be stuffed into the traditional Altoids tin.? ;-)
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Jerry, KE7ER
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On Wed, Jan 1, 2025 at 11:22 AM, Hans Summers wrote:
Nuts, yes! Welcome to my life.?
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> I understood that; you are handling it before >? it hits customers for everything except the? > QMX, however even you having to deal with > a 15% failure rate on a component is nuts > (for you to have to deal with).
Nuts, yes! Welcome to my life.? QMX is the outstanding problem. We will find a solution to that too.?
The QMX boards could be tested with some sort of bed of nails test fixture that provided the appropriate test signals for IC403 couldn't they? Use the CLK2 signal attenuated by R513 with a suitable level and phase shift, then the Rx Audio and Image tests should work.? That's enough to test most of the Rx side on an unpopulated board.
Yeah like my QCX-mini test fixture:
It took me 3 R&D-Weeks to build that. I shudder to think how many actual elapsed weeks it would take me to do that now. Arrrgghhhh. But yes it's an option I'm considering... The complexity and number of test pins could be greatly reduced if looking for one specific fault rather than trying to test every aspect of the entire radio.?
I guess you don't see the PCM1804s until they arrive on boards.? Has your trusted supplier been caught by someone flogging clone ICs?
Nope. That would be too easy... Anyway I have never seen anything other than absolute loyalty in the last 11 years working with my colleague in Shenzhen and I'm sure he would never cheat me. He knows what side his bread is buttered on. Issues further along the supply chain (in other words him being cheated, or suppliers of his suppliers) are harder to be so sure of. A messed up world.?
73 Hans G0UPL 73 Hans G0UPL
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On Wed, Jan 1, 2025 at 08:52 AM, Hans Summers wrote:
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QMX is the outstanding problem. We will find a solution to that too.?
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The QMX boards could be tested with some sort of bed of nails test fixture that provided the appropriate test signals for IC403 couldn't they?
Use the CLK2 signal attenuated by R513 with a suitable level and phase shift, then the Rx Audio and Image tests should work.? That's enough to test most of the Rx side on an unpopulated board.
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I guess you don't see the PCM1804s until they arrive on boards.? Has your trusted supplier been caught by someone flogging clone ICs?
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Chris, G5CTH
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I understood that; you are handling it before it hits customers for everything except the QMX, however even you having to deal with a 15% failure rate on a component is nuts (for you to have to deal with).
toggle quoted message
Show quoted text
On Jan 1, 2025, at 8:52?AM, Hans Summers via groups.io <hans.summers@...> wrote:
To be clear again: I'm saying 15% of the batch of 1000 QMX+ Rev 2 PCBs was rejected during our testing here. The percentage of Rev 2 QMX+ with faulty PCM1804 that reach actual kit builders should be near zero.?
QDX is a similar story. We test for it here.?
QMX is the outstanding problem. We will find a solution to that too.?
So in other words, QDX and QMX+ are purely my own internal problem now. Issues for the kit constructor should be very rare. QMX is still an issue I'm working on and needs to join QDX and QMX+.?
73 Hans G0UPL
Yes, remarkable that the PCM1804 saga continues. I built 4 QMX and one QMX+. Only one had an 1804 failure. First Rev 1 and Rev 3 (mini) had/have no failures. Second Rev 1 had SMPS (5V), then Mplx chip failures. Both replaced and all well. Rev 4 had 1804 failure - replaced and all is well. In fact, that is my go-to mid-band rig for portable operations. QMX+ no problems. In addition, 2 QDXs before had no issues with the 1804s. Both QDXs sold since I have the QMXs.?
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73, Dan? NM3A
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To be clear again: I'm saying 15% of the batch of 1000 QMX+ Rev 2 PCBs was rejected during our testing here. The percentage of Rev 2 QMX+ with faulty PCM1804 that reach actual kit builders should be near zero.?
QDX is a similar story. We test for it here.?
QMX is the outstanding problem. We will find a solution to that too.?
So in other words, QDX and QMX+ are purely my own internal problem now. Issues for the kit constructor should be very rare. QMX is still an issue I'm working on and needs to join QDX and QMX+.?
73 Hans G0UPL
Yes, remarkable that the PCM1804 saga continues. I built 4 QMX and one QMX+. Only one had an 1804 failure. First Rev 1 and Rev 3 (mini) had/have no failures. Second Rev 1 had SMPS (5V), then Mplx chip failures. Both replaced and all well. Rev 4 had 1804 failure - replaced and all is well. In fact, that is my go-to mid-band rig for portable operations. QMX+ no problems. In addition, 2 QDXs before had no issues with the 1804s. Both QDXs sold since I have the QMXs.?
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73, Dan? NM3A
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Karl
Bruce Akhurst
Kaufman, Matt - N3AR