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Hello. I was using my QMX on 40m and 20m FT8 with a known good antenna and computer connection, successful QSOs, and no SWR lock outs or other signs of issue.?
The QMX screen went to all backlight with no LCD characters displayed for 1-2 sec and then went to a mix of full block LCD and some apparently random characters. Screen has no obvious physical damage. I was not transmitting at the time.?
I attempted basic battery / power troubleshooting to no avail. With a known good power source, it will not power on. Confirmed it is not limited to a screen issue, there is no RX as tested with audio output.?
What other troubleshooting is recommended? I’m ok with basic electrical repair, but don’t see myself doing and surface mount repairs. And I’m hoping there’s a possible test to rule out failed components and possibly an easy fix.?
I have explored the archives and didn’t see a similar problem noted. Thanks for any help.? |
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Can you measure the current draw from your power supply to the QMX in the following three conditions:
1 - while QMX is powered off (remove power cord, then replace it to make sure QMX is off).
2 - while you are pressing the power-on button?
3 - after you release? the power-on button (which is when it should be powered on).
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That will help determine what state your QMX is in. |
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On 29/03/2025 12:17, Brien - KE7WB via groups.io wrote:
Plug in the USB cable from computer to QMX and then try to turn on QMX. This yet to be fully understood scenario worked for me on a couple of occasions.Brien, This really needs to be emphasised in the manual. Right from the first QDX it has been necessary in Windows to power cycle the QDX/QMX after the computer has been rebooted. A QDX/QMX will only enumerate once per power-up. I believe Hans has the answer but it does not seem to have an immediate solution. 73 Alan G4ZFQ |
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On Sat, Mar 29, 2025 at 01:17 PM, Brien - KE7WB wrote:
Plug in the USB cable from computer to QMX and then try to turn on QMX.? This yet to be fully understood scenario worked for me on a couple of occasions.Brian, if this works when you can't switch on your QMX without the USB cable something is wrong with your setting / your QMX!!! ?
73 Ludwig |
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On Sat, Mar 29, 2025 at 10:26 AM, @Ludwig_DH8WN wrote:
Possibly, but it has not happened to mine for quite a while (so no opportunity to explore further) and my QMX has been working fine.? I did add some ESD mitigation and have not had any abnormal operation since. ?
Brien - KE7WB?
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Stan,
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I connected a Fluke 289 in series on the +DC leg of a 12 VDC power adapter measuring 13.4 VDC output at open circuit.
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QMX was unplugged to ensure it was off.? Plugged in with the barrel connector downstream of the Fluke set to measure DC mA: 0.002 mA in OFF state
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With power knob depressed, current measured was 9 mA. Initially, this spiked to 7 mA and dropped off to 0.002 mA with button still depressed.? Second time around, 9 mA was very repeatable with power knob pressed.
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When power knob is release, current drops to 0.002/0.001 mA which I take as zero through-out the experiment.
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Ludwig,
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I attempted a power up after connecting to USB port on a computer.? No luck.
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Generally,
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I was reliving the failure and noted my input voltage was displayed as 10 VDC which I was concerned was low and may have led to an over-current.? But, I noted that the operating input voltage range is 6-12 VDC.? That said, I've since discovered that the AC/DC adapter I was using did have some intermittent supply issues and I may have had a supply voltage drop while transmitting or something.? I suspect I'm headed for a new SMPS board repair.? Input and advice has been appreciated and more is welcome.
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Sure have missed having this radio operating.? I didn't realize how attached I had become!? Thanks to Hans and others for making these reality.? Looking forward to getting back on the air.
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-Chris |
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On Thu, Apr 3, 2025 at 10:26 AM, <k2cwcqrp@...> wrote:
a 12 VDC power adapter measuring 13.4 VDC output at open circuitIf this is the power supply you have been using to operate your QMX, that is what caused the problem.? 13.4V is too high a voltage for QMX, as explained (in boldface red) in the assembly and operations documents.? Hans recommends using 2 simple silicon diodes in series in the power cable to lower the voltage, or you can use a buck or buck/boost converter.? Using 13.4V will eventually cause problems, like possible damage to your finals and to your power supplies.? If the supply voltage goes down lower than 12V during TX, it is still a problem, since it will bounce back up to a too-high voltage.? And if it droops to lower than 12V during receive, then it doesn't have the current capacity to properly power your QMX, and will cause operational problems.? ?
And if you weren't using that supply, good.? But you shouldn't use it for diagnosing the problem, either, unless you can turn it down to about 7V and set a 250mA current limit.
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But back to the current problem -
If all is operating correctly, your current while pressing the button should go up to about 200mA for about 1 sec, then settle down to about 100mA after the processor starts up the SMPS supplies.? None of that appears to be happening.? Which means the 3.3V linear supply isn't even turning on - and that just requires hardware switching, so something is definitely broken.?
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If you are up to doing some measurements, disassemble the QMX enough to remove the two power supply units, and test them independently using the procedure in the wiki. ?/g/QRPLabs/wiki/37128.? If one or both of these is bad (and you don't want to try fixing SMD stuff) you can order a new set from qrp-labs for $10.
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Also on the main board, measure the resistance of the 12V, Vcc and Vdd pins with respect to board ground and with respect to each other.? These should all be at least a few k-ohms, if any is instead just a few ohms, that means something on the main board is shorting and needs to be found and fixed before installing and using new/fixed power supplies.
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Or you can punt and send it to Jeff W1NC and he will fix it for you - but where's the fun in that?
Good luck - let us know how it goes.
Stan KC7XE
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Thanks Stan.
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That power supply was labeled as 12 VDC output (just a wall wart). I was a bit surprised to measure 13.4. The reminder and caution on using it is appreciated. It isn’t the one that was being used for operation, that one was flaking out so I had to swap a different one in. May be time for a real power supply.?
I’ll get inside and do the additional diagnostics. |
Brien - KE7WB