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QMX shows 3v3 SMPs board stuck in linear
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Hello folks, my new QMX build initially showed up as a drive on my computer so I loaded the latest firmware and then cycled power. I got nothing on the QMX display so I tried terminal mode. Terminal mode just goes right to the diagnostic screen and shows ??3v3 SMPs board stuck in linear. Sent pictures to Hans and he is happy no components are missing from the 3v3 board. Has anyone come across this and fixed the issue please?
Thanks Robbie |
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Robbie, you should check the 3V3 SMPS (PCB #2) off line (see here).
Your 3V3 SMPS is working full speed (Duty cycle = Duty max) but not enough outcome. In this QRP Labs Wiki document you find a description of the switch on process. In your state you may check the signal ADC_3V3. It's the half of the SMPS produced VDD. How much is it? TAKE CARE not to connect different points of the SMPS pin header. This may destroy your QMX. 73, Ludwig |
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This looks very familiar to me.
On the diagnostic page do not worry about the 5.63 volt report. That is because the output of the 3.3 linear supply is probably more like 3.1 volts, and that is being use by the microcontroller ADC as a reference voltage. My problem was that the inductor up by the nylon screw on the 3.3V power supply board was broken. The nut is a little too large, and if you turn it, you can easily catch the thin wire in the inductor and break it. I was able to do a bad repair job, and the power supply sprang to life. Test your inductor for opens. It was hard to get to the pads of the inductor for me, so I ended up testing from the + of the capacitor to a diode. Of course, your problem could be anywhere on the right hand side of the 3.3V SMPS schematic. If your problem is not the inductor, take voltage readings (best with a scope) along the elements of the switcher and post them here. Mark W8GU |
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Dear Robbie,
I was building a QMX+ and I had the same indications on my power supplies.?
I think I have an intermittent short on my board but can't seem to find it ... Eventually the little transistors on the left side of the board
starting getting hot.... Now it no WORK at all... Here is my diagnostic chart:?? It looks just like yours.
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I had the same issue.?
When looking at your photographs it looks like you cut the connection between the middle connector pin and the closest transistor pad.
This is what I did, thinking that there was a solder bridge.?
But the middle connector pin shall be connected to the transistor pad.?
Other remark: the soldering do not look good, but the picture is unfocused, so not easy to see.
You should verify good connection between connector and board trace.?
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Gunnar /SM5EIE? |
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Hi Gunnar, initially I was trying to make sure there was no shirt on the middle pin but then I opened a ticket to check and Hans confirmed that there should be continuity between these two points so I left it. I did verify each connection as I made it but there is obviously something wrong so I’ll recheck them.?
I appreciate you taking the time to respond and I’ll post updates at the end of the week when I get a chance to continue working on my little radio.?
73 de gi7fdz |
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Tim Tucker
My QMX was also stuck in linear mode (PWM was at max, ADC_3V3 was less than 3v).? Thanks to W8GU for suggestion to check the inductor on the 3.3v supply.? I was able to measure a continuity issue, and then spot the broken wire, as per photo below:
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I was able to carefully scrape insulation from the broken wire and establish a connection to the board as per photo below:
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Unit now properly moves to SMPS mode, and Main Menu appears.
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Tim
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