I just finished building a QMX+. Initial power up was fine with current about 200 mA at 9V. The transformer is wound for 9V. My computer recognized the QMX and I was successfully able to download firmware version 1_00_027. Transceiver display after initialization was incorrect. I will include a picture but it is a series of solid rectangles arranged horizontally along the upper portion of the display. I installed a jumper as per the instructions to force a download and opened the QMX file on my computer which confirmed that the file had successfully downloaded. Tried installing an earlier firmware version with the same result. I am assuming that I have a bad solder joint going to the display but the design of the front panel makes this a little tricky. I am hoping that someone in the group has seen this before and can advise me.

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This my second QMX transceiver build and the first worked perfectly from the start. I have really been impressed with the unit. Hopefully the bad connection will be easy to find. Thanks?

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What happens when you adjust R305, the screen contrast potentiometer?

Double check the solder connections on all of the through pins that connect the display to the board with the front controls (not sure what it is called, but the board with the encoders, buttons, mic, battery, etc.).?
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I had some display issues with mine that were fixed by cleaning up the solder joints on either side of the through pins.

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Steve KA0SM

I assume it powers up and down properly using the top knob, but draws 200 ma.

So the processor is working, but not yet convinced that the power supplies working.

If you look at LIN_REG_EN on the first page of the schematics with a voltmeter,

it is probably still up around 3 volts indicating that the 3.3v SMPS is not yet selected.

Once the supplies are working, the processor lowers LIN_REG_EN and the rig draws less than 100 ma.

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The fact that the display shows the black blocks says that the 5v SMPS is at least partially working

providing 5v to the display, but that the processor has not written a message to the display yet.

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Check the voltage across C106 and C107, those should be 3.3v and 5.0v respectively when they are working.

If you have a scope, check to see PWM_3V3 and PWM_5V, they should both have a square wave of about 116 khz,

and be high somewhere between 1/4 and 1/2 of the the time.

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I am not certain of the exact sequence that the power supplies come up.

My best guess is that PWM_3V3 and PWM_5V are both active immediately after the processor starts working,

and that it waits till both ADC_3V3 and ADC_5V must look good before the processor?writes messages to the display.

No idea if LIN_REG_EN goes low when just ADC_3V3 looks good, or if the processor waits till ADC_5V is also good.

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Jerry, KE7ER

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On Sat, Nov 30, 2024 at 11:06 PM, Robbie WN6AMS wrote:

Not sure what to say? I double checked all the solder joints on the connections and touched up any that seemed to be at all suspect. Using the schematic for the front panel board traces I made a diagram of the terminals at the three connectors that move data from the main board to the front panel. I then checked continuity from the solder pads on the back side of the main board to the display panel and other components such as the encoders and board surface-mount components. Using a pin probe I did find one connection on the display board side where the pin may not have been connected to the solder pad which I touched up. Connected the two boards and adjusted the contrast trimmer pot and the display lit up. I did notice that the pot had to be adjusted to the stop for the letters to appear. This setting may have been the actual problem as I may not have moved the control to its extreme before. Great everything works properly and I was able to enter all of my standard settings. Powered up and normally shut down the unit multiple times. Again everything seems to be working properly so I put the cover back on and hooked the unit up to an antenna for testing.

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Now the unit is not powering up? I am monitoring current flow and there was no power surge so it is simply not energizing when I press the Volume Encoder? The only thing I can think of is the encoder? A couple times previously it seemed that I did have to press the knob multiple times to power up? I am not sure how the encoder is configured so I don't know how to check its operation? Life is funny sometimes! I went from fantastic to you got to be kidding me in a heartbeat. I am enjoying myself and learning some new tricks which is the important thing. I am going to give it a rest for today and try again tomorrow. Thanks for your help and comments.??

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On Sun, Dec 1, 2024 at 10:43 PM, Robbie WN6AMS wrote:

so I put the cover back on and hooked the unit up to an antenna

Robbie, doing this maybe you bend the PCB a bit and a cold solder joint loosed connection?

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As far as I can see, it's a rev. 1 board ( with two SMPS subboards). Connections between the SMPS boards and the main board are important for power supply and switch on / off. Reading QMX QMX_plus Startup section 2 you will find a description of power on and which signal should have which level at which step of the switch on process.

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It looks like you stuck in step #1.

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You may check the volume encoder push button (the encoder side with only two pins).?

Please check all solders of the connectors from the SMPS boards to the mainboard.

When you find no problem you may check the levels of the signals using your DMM (see QMX QMX_plus Startup section 2).

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73 Ludwig

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Interesting! I really appreciate the power on sequence information and circuit schematics as they were very helpful. With the information you gave me I was able to verify good continuity and encoder S304 switch operation back to connector JP201 at the solder pad on the main board. Next I looked at VDD & VCC which was 0V. So I went back to what I normally do first and looked at input voltage. The fact that that the transceiver was working intermittently fooled me. The problem is the 3.5mm dc power connector! I verified that I have 9V input but the voltage fluctuates down to 3V at the output terminals? Not a bad solder joint as I am measuring from the output tabs not the PCB solder tabs. The connector is faulty and needs to be replaced. I hate to put in an order this small to an online electronics supplier like DigiKey. I found a listing on Amazon for a similar item but the dimensions are slightly different. Do you have any suggestions?

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I am convinced that the connector itself is the problem but it is also puzzling? Before checking voltage I looked at continuity which is good. Triple checked my findings but with 9V in I measured 3-7V fluctuating at the connector tabs with no current flow. Must be a broken internal connection that is just rubbing together? Anyway I have learned a lot from the troubleshooting experience and it has been almost as much fun as the kit build. My background is industrial automation but I am retired and way out of date. Very satisfying that I can still do basic troubleshooting! Thanks again for everyone’s help as I certainly would not have been able to do this without help!

On Mon, Dec 2, 2024 at 07:32 PM, Robbie WN6AMS wrote:

The problem is the 3.5mm dc power connector! I verified that I have 9V input but the voltage fluctuates down to 3V at the output terminals?

The power connector should be 2.1 x 5.5 (2.1 mm inner diameter and 5.5 mm outer diameter). So I'm a bit confused.

Be sure you use a 2.1 x 5.5 plug and not a 2.5 x 5.5 plug. The last type fits into the barrel but is known for intermittent contact and serious problems.

Ludwig is correct.? Before deciding that it is the power connector on the QMX+ board, check your power cable.? The QMX uses 5.5/2.1, which is a popular and standard connector.? But another very popular and standard connector plug is the 5.5/2.5 (bigger hole), which will be intermittent on the QRP-labs gear.? Test your connector plug using a 2.5mm (#40) drill bit shank - if you can insert it, it is 2.5mm and should not be used on the QMX+.? It is very hard to tell just by looking at the connector.? Some 5.5/2.5 connectors will seemingly work well, but then fail when moved a bit.

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It certainly is possible that the connector on the board is bad, but I have heard of only one case of that happening, and many, many cases of people who discovered they were using a 5.5/2.5 connector plug.

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Stan KC7XE

The pigtail being the wrong size makes a lot of sense given my voltage and continuity readings. I am using the pigtail delivered with the QMX+ kit. Will check this and get back.?

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Checked the power plug with a 2mm drill bit and it was a tight fit so the plug is the right one. Also assuming that the QMX+ uses the same connector as my previously built QMX and QCX-Mini I connected it to my portable battery supply which I have been successfully using with both radios for quite some time. Voltage reading results were similar. So not the cord but an easy fix. I should have the new connector sometime on Wednesday and I will let you know how that works out. Again thanks for your help as I would have ordered the wrong power socket otherwise. I am tempted to remove the broken socket and attach temporary connection wires so I can finish the testing phase.?

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Some have replaced it with Anderson power poles. I ams also thinking of doing that.?

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73, Dan - W2DLC

A while ago there was a message about a broken barrel DC power connector. Something was wrong inside the connector.

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73 Ludwig

On Mon, Dec 2, 2024 at 11:45 PM, @Ludwig_DH8WN wrote:

a broken barrel DC power connector

To be clear, it's the part solderd to the QMX PCB.

Yes I was discussing the part soldered to the PCB. But, to be honest I am now at a loss as to the problem? I removed the socket from the printed circuit board and retested it with nothing connected to its terminals and could find no problem? Put the cable back in the socket with nine volts and the voltage was steady even when I wiggled it. The reason I didn’t believe it was a bad solder joint was I was measuring voltage directly from the metal tabs on the socket not from the PCB. The power supply was indicating zero current flow so voltage drop across a bad connection also doesn’t seem to be the case. The voltage was varying wildly from 3 to 7 V so your suggestion that the connector was the wrong size makes the most sense. Yet when I put the same connectors together by themselves on the work bench they work fine??

Good news is I temporarily soldered power lines directly to the PCB and the transceiver seems to work normally. Measured VDD at 3.3 V and VCC at 5 V from the PCB. I am just starting my testing but I can receive and transmit on 20M at full rated output and the functions that I have tested so far have functioned properly. I also transmitted a CQ which was received by a spotter on the Reverse Beacon Network so I have confirmed that the unit is transmitting!

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So, I am quite confused as to the cause but extremely satisfied that the unit is working! Which is the important thing. Again I cannot thank you enough for your help! I would have had difficulty even starting the diagnostics without assistance. I built two Heathkit transceivers in high school (1972). One for my brother and another for me. I fell out of the hobby and came back last year after a 45 year gap and being able to build my own transceiver has been very special. Not to mention that my wife is very happy about the low cost. That and the fact that I can troubleshoot this complicated of a circuit has been extremely gratifying!?

Dan,

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The transformer in my transceivers has been wound for a 9V input. I use a INIU 2000 mah Power Bank in combination with the DSD TECH Type C PD ?to DC power cable at 9V output. The cable comes with a connector that works perfectly with the QMX and it all fits in your pocket. I have found that this supply has more than enough capacity for these transceivers and the power cable regulates a steady 9V output so I don’t have to worry about overdriving my transistor finals. Thank you for your comment.

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Robbie

WN6AMS

Dan,

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I have attached a screenshot of the power bank and power cable that I have been using . The same company also makes a 12V version of the power cable if your radio has a transformer wound for that voltage.

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Just adding a shot of the QMX+ in service. I should have the new part tomorrow so I will be able to finish the build.

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I received the replacement DC Power Connector PCB mount female plug yesterday evening from Amazon. The price was less than ten dollars for twenty replacements so very low cost. Last night I soldered the new part on the board and the transceiver seems to be working normally! I checked power output in all bands and my meter was indicating slightly over 5W. The bands were fairly quiet last night night but I also listened to a few stations on 40 & 20M.?
I have included a shot of the working QMX+ faceplate. Great little transceiver and I have finished it just in time to take with me on a trip!

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Enjoy your new radio. I received mine from Turkey already built just last week and it is a joy to see and use sitting next to my K2 and K3s….. I might as well put dust covers on the K2 and K3s as they won’t see much use for quite a while. ?It was especially interesting to plug the GPS antenna (I had Hans include the GPS receiver in my build) on the back and see the various parameters show up on the screen. ?I had the same joy when I plugged the QLG1 into my first QCX a few years ago….. next I will put the battery in the rig to run the clock. ?What hasn’t Hans left out besides SSB and that is getting closer? ?He keeps finding new ways to improve and extend the abilities of this radio, far beyond my pay grade. ?I would like to see the current draw when his brain is in full tilt on some new feature….. hope he doesn’t blow a fuse. Ha!

Again, have fun. ?I have been a ham since 1960 and am still amazed at what our ham friends have developed over the years as each new mode and integrated circuit became available. ?I still enjoy portable CW the most but look forward to using low power SSB when it becomes available.