52 tips for building your QMX successfully!

The QRP Labs QMX Multimode Multiband QRP transceiver kit is an amazing combination of performance, features and low price in a very compact package. We have at the time of this video production, assembled something like 60-70 QMX transceivers here at QRP Labs Towers. This video contains my observations of some common pitfalls to avoid, and tips for successful assembly.
QMX: qrp-labs.com/qmx
Some of the 52 tips may be obvious to you, many are in the assembly manual (which of course you will read word to word, cover to cover); but I suspect the majority of constructors will find at least something useful in the video. QMX is a compact build. With care and attention to detail, you should achieve a functioning, high performance transceiver.

[@Dihydrousoxide]

Timestamps / Chapters
0:00 Intro
0:25 1. Read the Manual
1:04 2. Choose a Quiet Time
1:54 3. Don't try and do too much in one session when you're tired.
2:17 4. Use a jeweller's Loupe for close inspection
2:53 5. Check for broken inductors / capacitor
4:24 6. Removing PCB rail may be necessary but is no big deal
5:06 7. How to snap apart boards
5:29 8. Some board edges need to be filed smooth after snapping out
6:28 9. When filing, don't fear internal copper layers. There's no risk.
7:20 10. File left and right edges flat so the enclosure fits later.
7:55 11. Clear possible Q103/Q104 short (PCB Rev 1 only)
13:09 12. Touch up USB-C connector but don't panic about it
14:31 13. Don't fail to remove wire enamel
16:23 14. Don't tin 0.6mm copper wire before putting into board holes.
16:15 15. Squeeze toroid turns to improve output power if needed but don't panic about the half dB.
17:49 16. A powerful iron and extra care and heat on ground connections.
19:19 17. Be careful not to break 47uH axial inductors
19:37 18. Avoid mixing up capacitors; don't rely on matching yellow/blue colours
20:22 19. Early instruction manual had 20m Low Pass Filter capacitors swapped
20:57 20. Early build manual, low 20m sensitivity dye to parasitic resonance
21:43 21. L401 inductor tip for easiest inductance adjustment later
22:13 22. Check trifilar windings carefully with DVM before installation
23:18 23. Beware diode polarity
24:29 24. Soldering iron from a clear approach path
25:19 25. Sharp wire cutters from a clear direction to avoid SMD damage
25:53 26. Keep wire cutters horizontal, squeeze don't pull
26:13 27. Beware very small gap between power connector and pin header pad
26:31 28. Watch out for other close-spaced pads such as at 3.5mm connectors
26:40 29. Special care at rotary encoder pins: risk of shorts to ground
28:38 30. Cutting technique for the control board header pins
29:55 31. Ensure perfect positioning of SMPS boards: connectors are raised a little
30:15 32. Don't drill or burn out the thread of the inner nuts
30:52 33. Move bolt as far from corner pillar position as possible
31:35 34. Solder side of the SMPS connectors in place then remove and solder other side
31:47 35. Position all inter-board connectors as accurately as possible
32:26 36. 3.5mm connectors need twisting to align at right-angles
32:52 37. Use of heatsink compound paste?
33:40 38. Bolt transistors down flat before soldering
34:15 39. Don't worry about BN43-202 transformer overhang
34:37 40. Zeners shown on schematic aren't supplied or installed or mentioned: not a mistake
35:07 41. Don't over-tighten the PA transistors bolt (PCB Rev 1 only)
35:43 42. Alignment of the BNC connector is important to get right
37:01 43. Don't forget to fold in the display tab
38:05 44. Trim LCD wires short
38:26 45. Winding style of the SWR bridge: copy manual photos
38:53 46. Don't forget to solder all connector pins
39:52 47. Don't forget to solder the underside of the SMPS board connectors
40:24 48. On completion check board carefully for shorts, poor joints, etc.
40:57 49. Check that no SMD parts have been accidentally knocked off the board
41:47 50. Enclosure screws should not need forcing in
42:11 51. Knobs need to be raised a mm so that there is clearance to press them
42:36 52. There's no need for the BNC washer and I like to leave it out
42:55 Good luck

[@Steve-GM0HUU]

Thanks for that. Very handy checklist.

[@hb9hwf]

Thank you, this is very helpful!

[@Steve-GM0HUU]

👍Thank you Hans for taking the time to do this. I will watch this again before I start the QMX build. The tip about NOT tinning the toroid leads is good - that would have probably caught me out. What occurred to me most in this video is that it is a very good idea to make sure you have good quality small sharp flush wire cutters for the build.

[@gravestonemyth]

I greatly enjoyed building mine. I knew nothing about the component shorting on the buck converter until after I finished, so I guess I got lucky. I did encounter a short between the body of the left encoder and the center pin of the power jack. I filed the encoder and desoldered and moved the power jack out a little past the edge of the board. I overheated and melted the speaker jack, which I have since replaced. I also had to trim the head of the nylon screw for one of the buck converters to get the case to close without interference. I’m getting around 5W on all bands without making any adjustments, so I was either lucky or good (or both). All in all, a challenging yet rewarding build, to say the least! Well done, mate! Now, about that AGC… DO NOT use headphones on this rig until the AGC feature arrives (it is not there in 1.0.9). My hearing took a hit after one particularly strong signal.

[@larrychristensen5917]

Great video sir. I built my QMX that worked straight away. You have covered all points to make the QMX build go smoothly. Thank you Larry NA0F

[@jma8352]

Great advice, not just for electronics but as a woodworker and builder, you have to have th right attitude and focus.

[@hb9hwf]

I finished the assembly and I am waiting for a SMPS board replacement to solve Q103/Q104 short problem. This video is extremely helpful to reflect on various tricky aspects of the build process and check all those points while I am waiting. This is the kit project I learned the most from and from which I gained the most experience! A lot of fun! That's due to you dedication for explaining and supporting builders. Thanks a lot for that!

[@BackcountryGearShed]

I just finished mine last night. I haven't tested it yet, but I applied power and it didn't let the magic smoke out so that's a win in my book. I had a moment of panic when I first powered it on and nothing happened, but I plugged it in to a PC and sure enough it showed up as a flash drive. I extracted and copied the firmware over and bam, it came to life! It's a great kit with very thorough instructions. I'll probably build another with the other bands in the future. Cheers!

[@johnpawlicki1184]

I have at over a half of a century building and modifying electronics. I always read the manual completely before starting the build. Sometimes people think I am brilliant but it is simply reading the instructions. ;-)

[@Steve-GM0HUU]

I can relate to what Hans said that there is maybe a risk that more experienced constructors don't carefully read or follow the manual. When I was younger I was sometimes afflicted by "I know better syndrome". However, eventually dawned on me that manuals written by experienced engineers (perhaps involved in the design of the equipment) are probably worth paying close attention to.

[@teuluPaul]

Many thanks Hans - fantastically detailed as always. My kit is still in a box, but I will get to it after the 16th October. Before I start, I will watch this again, and print out and read the latest instructions. As I complete each step, I will tick it off on the instructions to make sure I don't miss anything. Biggest surprise for me from this video - the need for a 60w soldering iron. I would possibly have reached for something smaller (unless of course this is also in the instructions :) ). You are a star!!

[@ericfox507]

Hans, thank you for these wonderful transceivers, the QMX being the latest, they are truly amazing. Thanks for these tips as well. Will start building my QMX kit soon.

[@AA7EE]

Good information and useful amount of detail. Thank you for taking the time and trouble to do this. I'm looking forward to putting together a QMX in the (hopefully) near future.

[@redtide08]

Thank you so much for going for the through hole usb c port. Structurally weak USB ports are a personal pet peave of mine 😂

[@krahwinkel9503]

Thanks for the tips and hinds - will become quite helpful.

[@babblebits8318]

To prevent a possible short (because my spacing was, well, non-existent) on the back-side of the 9v/12v power socket, from a fairly large piece of shrink wrap tubing, I cut a small square, single layer (half the tube) and just wedged it between the back of the power socket and the adjacent jumper pins component. I did not heat it, but it was what I had lying on my bench that was thin and would make a good insulator. I had to do this because I soldered the power socket just a tad back from the edge of the PCB. The front of it needs to be right at the edge so the back-end of it (with +12V spot of metal) clears the jumper pins that are installed later.
I have a 110W soldering station, and even with that amount of power I was surprised (even though Hans has discussed this several times) at how long it took to solder the through-hole components to the PCB. My first impression was that the metal used in the PCB did not take solder well (I chose lead based solder); but that was not the case at all, it just takes a surprising amount of heat and therefore longer time for solder tip contact with components to get a good solder joint due to the 6 layer PCB used. I did use a rather blunt soldering tip to help improve the heat transfer. I also did not trust just using heat to burn off enamel for any of the toroids; I scraped all enameled wire connections prior to soldering them, then tested every one of them for continuity with a Digital Multi-Meter.
All-in-all, it was a fun build. I completed mine over a 3 day period, and was on the air with my QMX the very next day after the build with no issues! (I did a current-limited under-voltage power up as recommended for first application of power). From my QTH near Denver Colorado, and a vertical antenna (a 20+ yr old Cushcraft R7000 w base up about 10 Ft) I have confirmed FT8 contacts to Somoa, Japan, Italy, Spain, Panama, Cuba, Ecuador, Switzerland, Canary Islands, Madeira Islands, Netherlands, Dominican Republic, Saint Vincent, Barbados, New Caledonia, and Hungary. All on the QMX running just under 5 watts over the last 3 weeks into a half-wave multi-band vertical on 40M, 30M, & 20M bands. And I have made many domestic US contacts on both FT8 and JS8Call.
I'm totally enjoying this QMX much more than I thought I would! Thanks Hans for producing this video. I wish I had seen it before I built my QMX, but the assembly manual is quite complete and clear, so had no trouble building the QMX. I'll be purchasing and building a high-band version of the QMX when it becomes available!

[@SpeakingArrow]

OUTSTANDING video and information. Could have applied many info points to earlier QCX builds. Just great Hans!

[@billclark148]

Thank Hans you for all you are doing for us. I did damage my RSPS #1 Board and need to replace it, I ordered a pair and a spare for future OOPS'. I also had a heck of a time following a few instructions but I believe my issues are going to be not using enough heat for blend the 6 layer boards connectors, that said I have not been able to power up my project enough to see it on my computer. There is Zero amp draw on my Variable PS set to 7V. I am hoping my replacement PS boards fix this issue.
Bill W3SI

[@RagnarEE]

Just ordered👍😀 Really looking farward to this build 🤗

[@JxH]

#40. Zener diodes. Many (many) years ago, this was an active topic (perhaps in QST or one of the ARRL books, e.g. the Doug DeMaw sort). One conclusion was that the zener diodes' capacitance was rather dominating the effect, and any suppression of transients or spikes was as much from the capacitance as from any zener or avalanche function. Not a chance that I can recall the exact reference after so many decades.

[@TheFretman2]

Thanks for the video…I’m starting on my QMX next week.

[@Bartok_J]

Thanks for this. Seems that my Rev 1 board (that I've not got round to building yet) WAS one with the PSU short. Happily, I can fix this before before it does any harm.

[@Wowfacter]

Very nice to have & see visually!

[@JxH]

24:13 Scratching screwdriver across the coils. Concept of the day, "Mechanical Sympathy". LOL 🙂 !!!!

[@StefanDc4kjs]

Thanks for the very good Video. 👍

[@ynot6473]

all very good, but i'd personally pay the extra for someone who knows what they're doing to put it together. i did that for my QCX mini.

[@Stefaon]

Hello, at 35:08 you show the screw for the PA.
The one I received with the kit have a larger head, it's touching the C503 caps. So I switch for a smaller one.
I don't know if it's important...

[@michaellanders1601]

I failed on the 40 and 80 dct Leon from Australia

[@jdotson41041]

Where are the instructions and doc manual located on your Web site I'm sure I overlooked it sorry

[@RonanCantwell]

#41 !! Hmmmmm... Don't like that at all. I've now cut and fitted a small piece of mica insulator to go under the screw head which should prevent any shorts.

[@resuscitationpicture]

sober and no argument with XYL - I'm afraid you're 10 years late with the QMX in my case, hi

[@Kim-bc3cr]

Promo*SM 🙂

[@Ham-dk9ty]

Not a kit to build.
Be warned
I got two of these radios and none of them worked.
There is no repair service available.

[@jameshall5835]

Thank you Hans !! I’m in the middle of my build and I found this VERY valuable. 73 de WB4YDL

[@danamarcy5414]

Thanks Hans. VE6KBI