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2nd QMX Build and it wont power on and an update on my old unit...
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Good morning,
I have received and built my second QMX according to the current build guide, and cannot get it to power on. I built it for 12v operation and I tried starting at 7v and then up to 10v (painful past experience). I know the screen will be blank and off until the FW is loaded. The unit does not even power on enough to be recognized as a USB device. I tried reflowing all of my connections on the main board as well as the connections on the buck converter boards and I even reflowed the USB port.? My first QMX had a bad day from the word go (fed with almost 14v by accident), and it will power on now after many repairs and much troubleshooting, but has no RX, I believe I may have fried one or more of the of the a/d converters on the main board but I do not know what part to replace them with, there are too many options. Maybe Hans can speak to that? Thanks, Devan KD8MST |
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Hello Devan There's only one ADC on the main board which is the PCM1804. But I'd suggest first checking what you see on the RF sweeps (apologies if you've already posted that here, too many topics to follow).? 73 Hans G0UPL On Wed, Aug 30, 2023 at 5:46?PM Devan Phillis <devan@...> wrote: Good morning, |
开云体育Have you tried the power boards one at a time from the old unit that does power up in the new QMX?73, Cliff, AE5ZA
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Hans,?
The sweeps were terrible. And I have no audio out of the 1st QMX. I worked with John Zbrozek a good bit with the 1st unit and we got it that far and we decided that the PCM1804 was likely bad. I went looking for a replacement and found several models on digikey or Newark (one of the two) but was unsure which to purchase. No you hadn’t missed replying before… I did however try to send you a private message on here a while back and I’m not sure if it ever even went…? Cliff, I did try swapping power boards from the old unit one at a time to the new. My old 5v board and my new 3v board allowed me to get the unit powered up to apply firmware, but now it will not power up again. Swapping the power boards every which way gives me no change now. And putting the old boards back into the old QMX sends it back to the way it was this morning when started…. I’m pretty confused haha. Thanks, Devan KD8MST |
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Hello Devan The fact that it has noise along there, not flat-lined, indicates to me that the PCM1804 is probably OK. You probably have an issue upstream of that. Could even be toroid enamel... or mixed up windings on the trifilar transformer. But my apologies if you have considered this already.? 73 Hans G0UPL On Wed, Aug 30, 2023 at 6:57?PM Devan Phillis <devan@...> wrote: Audio Filter Sweeps |
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Hans,
The trifiliar was one of the first things we did…. Also, I reflowed all the other places where enamel comes thru the board. I should mention that the 1804 gets warm… not hot but warm. I’ll look back try my emails with John and get an idea of where we were, it has been a while since I had the time to mess with it. I would really like to get the original going because it was one from Dayton and then the new one is obviously not. Also… I made a work around but a heads up, my 2X3 female socket connector was missing a pin. See attachment. |
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Hello Devan A technique I suggested for QCX troubleshooting was to bypass the signal generator resistor (120K in QCX, 100K R518 in QMX) with a much smaller resistor, say 330-ohms. Then the signals are enough amplitude that you can trace them through the LPF, BPF and trifilar transformer, with an oscilloscope. Signal tracing, oldest techniques, still valid. I don't think there's a problem in your PCM1804 or digital Signal processing. I'd guess it's in the filters or mixer. 73 Hans G0UPL On Wed, Aug 30, 2023, 7:17 PM Devan Phillis <devan@...> wrote: Hans, |
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