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QMX(+) Build experience, Poor Audio Filter Sweep/RF Filter Sweep/Image Sweep/ADC IQ test and resolution with new PCM1804

 

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.?
--
73, Dan? NM3A
 

A 15% failure rate for any semiconductor device is extremely high. Googling PCM1804 failures shows posts about high-level audio noise that randomly occurs and goes away.


Tony

On Wed, Jan 1, 2025 at 10:26?AM Zrinko Ivan Vukoja via <ivan.9a5czi=[email protected]> wrote:
Hi Hans,
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Yes, the problem is very strange.
In my case the PCM1804 worked almost correctly. The fault was only in the unequal amplitude of the I and Q signals. If I had not used the diagnostic tools in the terminal I would not have noticed the problem immediately.
What is common in all cases is that the problem is present from the first power up, and fault never appears later. That is why I suspect a fault in the PCM1804 manufacturing process.
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73 de Zrinko Ivan, 9A7AM
 

Hi Hans,
?
Yes, the problem is very strange.
In my case the PCM1804 worked almost correctly. The fault was only in the unequal amplitude of the I and Q signals. If I had not used the diagnostic tools in the terminal I would not have noticed the problem immediately.
What is common in all cases is that the problem is present from the first power up, and fault never appears later. That is why I suspect a fault in the PCM1804 manufacturing process.
?
73 de Zrinko Ivan, 9A7AM
 

开云体育

Wow - a 15% failure rate sounds exceedingly high.


73

-- Matt N3AR

On Jan 1, 2025, at 7:48?AM, Hans Summers via groups.io <hans.summers@...> wrote:

Hi Zrinko Ivan

My assumption is that the Chinese manufacturer does not install original chips, but copies that in many cases do not work well.

It isn't how it works. While the PCBs are manufactured and SMD assembly is in China, we don't use a Chinese manufacturer in the way that people submit a PCB and BOM to JCLPCB or someone (not saying there's anything wrong with JCLPCB per se).?

I have a trusted colleague in Shenzhen, a sub-contractor who I have worked closely with since 2014. Many of the parts are ordered direct from the manufacturers e.g. NXP Semiconductor, or Analog devices or from US distributors such as Digikey, Mouser and Arrow. Other parts like resistors and capacitors are sourced locally in Shenzhen from reliable sources but all the parts are tested by me and then the same suppliers used in all manufacturing batches. Everything is traceable and documented.?

Over the years there have occasionally been problems, things were particularly difficult during the global semiconductor shortage post Cv19. We've been able for the most part to quickly identify and resolve any issues that arise.?

The PCM1804 problem is a rather unique one that so far remains a mystery. Progress is being made. On QDX and on current Rev 2 QMX+ PCBs, we're able to test the board INCLUDiNG PCM1804 before shipment and I think we have a very high success rate at detecting failed chips. There was about a 15% failure rate in the batch, which were rejected here and not shipped to kit constructors. I don't think it's an ESD problem caused by the kit constructors.

So I think I'm making progress on the problem and hope to solve it finally got the QMX which is the remaining issue.?

73 Hans G0UPL
 

Hi Zrinko Ivan

My assumption is that the Chinese manufacturer does not install original chips, but copies that in many cases do not work well.

It isn't how it works. While the PCBs are manufactured and SMD assembly is in China, we don't use a Chinese manufacturer in the way that people submit a PCB and BOM to JCLPCB or someone (not saying there's anything wrong with JCLPCB per se).?

I have a trusted colleague in Shenzhen, a sub-contractor who I have worked closely with since 2014. Many of the parts are ordered direct from the manufacturers e.g. NXP Semiconductor, or Analog devices or from US distributors such as Digikey, Mouser and Arrow. Other parts like resistors and capacitors are sourced locally in Shenzhen from reliable sources but all the parts are tested by me and then the same suppliers used in all manufacturing batches. Everything is traceable and documented.?

Over the years there have occasionally been problems, things were particularly difficult during the global semiconductor shortage post Cv19. We've been able for the most part to quickly identify and resolve any issues that arise.?

The PCM1804 problem is a rather unique one that so far remains a mystery. Progress is being made. On QDX and on current Rev 2 QMX+ PCBs, we're able to test the board INCLUDiNG PCM1804 before shipment and I think we have a very high success rate at detecting failed chips. There was about a 15% failure rate in the batch, which were rejected here and not shipped to kit constructors. I don't think it's an ESD problem caused by the kit constructors.

So I think I'm making progress on the problem and hope to solve it finally got the QMX which is the remaining issue.?

73 Hans G0UPL
 

My assumption is that the Chinese manufacturer does not install original chips, but copies that in many cases do not work well.
?
73, Zrinko Ivan, 9A7AM
 

It's remarkable that you have had three PCM1804 failures even while using antistatic procedures. I built a QMX and a QMX+ without using any precautions, and did not have a chip failure. The PCM1804 mystery continues.
--
73, Dan - W2DLC
 

Good evening! Big thank you to Hans and everyone else in this forum! I had a lot of fun building these kits and I couldn’t have successfully completed them without the folks who ask and answer questions here. I wanted to make this post to thank everyone but also to detail some of the problems I encountered, the equipment I used, and also how I resolved them.

This is a long post for anyone who’s interested but TLDR: I built 2 QMX+s and 1 QMX and all three needed new PCM1804s.

I purchased a QMX+ in May and a couple weeks later got to work. I had built a couple other kits and antennas previously but this was the most involved so far. I was able to make it through the build and load firmware but I couldn’t run all of the self-tests and the audio was loud static. I didn’t have enough experience or equipment to troubleshoot myself but luckily Jeff Moor W1NC reached out and offered to help. See /g/QRPLabs/message/126274 for my original post. I mailed him my QMX+ and he got it back to me in about a week with several fixes. It had several bad joints, insufficiently scraped enamel, a bad PCM1804, and a bad inductor. Thanks Jeff for your knowledge, experience, and willingness to help the community with your excellent service! I’m extremely pleased with the outcome and my QMX+.

I used:

  • A Weller 70W digital soldering iron

  • 63/37 Kester .20 solder

  • 30X/60X loupe

  • LED Head Magnifier

  • Crescent shear cutter/pliers set from Home Depot

  • A couple of different helping hands type devices

  • Solder wick & plunger type desolderer

  • Flux paste

I primarily used the conical soldering iron tip with success but in retrospect, I should have primarily used the wedge tip. The head magnifier with 3x magnification, plenty of light, solder wick, flux, and desoldering tool were critical. The loupe was ok but the head magnifier would have been enough. I ruined the side-cutters on solder wick.

Pleased but not content apparently because in July, I purchased another QMX+ so that I could use the lessons learned from the first unit and hopefully successfully build another myself. The kit stayed in the box until my wife & kids went on vacation for about a week. Over a couple of evenings, I had a great time building the kit, using all my new knowledge and experience, but when running the terminal tests, I had bad results on Audio Filter Sweep/RF Filter Sweep/Image Sweep/ADC IQ test. I reworked some of my joints but to no avail. Some example scans, before and after 1804 replacement, are attached.

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With bad PCM1804

I started diving into groups.io posts and determined that maybe I should invest in more test equipment and that I might have a bad PCM1804 chip. I ordered two more PCM1804 chips (just in case I ruined one). I also ordered a QMX because I was more confident in my kit building skills. In the mean time, I also purchased an LCR meter, a TinySA Ultra (for its signal generator), and an oscilloscope. Probably overkill but I had my eye on them for a while.?

Over the winter holiday break, I built the QMX. I enjoyed and had more confidence in my build but I had very similar problems to my 2nd QMX+ build during self-tests. During this build, I used a grounding strap/bracelet the entire time so I was pretty sure it wasn’t static discharge related. What are the odds I’d have the same problem twice? I found this post /g/QRPLabs/topic/109639794#msg133769, indicating the PCM1804. I did the diagnostic tests from /g/QRPLabs/wiki/37111 and determined that replacing the PCM1804 was my next step. Luckily I had two new PCM1804’s in stock although I previously intended on only needing one.

After doing research here and on youtube for replacing SMDs, I got a ChipQuik kit and a hot air rework station. After doing some tests, I decided I would just use the ChipQuik, which is basically easy-mode for low-skill chip removal. My process was basically, remove the chip using flux and ChipQuick, clean the left-over ChipQuik with fluxed solder wick, clean the board with 99% IPA, flux the new chip legs, place the chip carefully on the board (head magnification essential), put a small amount of solder on the iron tip, tack the first pin, ensure chip alignment, then use the solder drag technique to solder the remaining legs. It doesn’t take much solder and I removed any excess with fluxed wick. I went back over the pins to ensure uniform connections and triple-checked for bridges. I repeated the process for the QMX+.

After replacing the chips, the terminal hardware tests all returned good results on both the QMX and QMX+. For good measure, I compared them with results from the QMX+ that Jeff Moore repaired for me and they were comparable. Once again, I’m super appreciative of all the folks here asking questions and giving helpful information. I’ve learned quite a bit about reading schematics, the function of different parts/sections of these radios, and test procedures. Thanks for everything!

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With new PCM1804:

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