Fellow Ham's QCX+ 5W CW Transceiver - 40m
Repair, Testing, Troubleshooting, and Assembly
QRP Labs QCX+ 5W CW Transceiver Kit, 40m -- Repair, Testing, Alignment, and Assembly
Repair - Display Board
The original Display Board (left, showing the 1x16 header installed backwards) and the newly assembled Display Board (right). The newly assembled Display Board (right) also used cardboard spacers added under each of the nylon nuts (between the display and the PCB) to get the board-to-board spacing to around 3.0mm.
Repair - Main Board
Burnt-off PCB pads/traces. There were numerous areas with burnt-off pads found on the Main Board. Most of the burnt-off pads were found on the solder side although a few were found on the component side. One of the many areas worked was in the JP11 area under R30, R27.1, and R27.2 as seen in the before and after photos.
RF BNC Connector. The RF BNC connector was seen not sitting flush to PCB. Desoldered, repositioned, and resoldered the connector. This would have been an issue when trying to install into the enclosure later.
L4 after rewinding for 16 taught and unkinked turns. Measured-in at 1.089 mH (as shown in the far right photo). Good enough!
The other toroids also had issues such as wrong turns (with one needing to be rewound as not enough turns), one wound wrong, and each toroid's leads needing the enamal removed for correct soldering. Each of the toroids (i.e.: L1, L2, and L3) after being checked out or redone, and the enamal removed from thier leads, was found to be "close" to the assembly manual's nominal value.
Even T1 was desoldered and the leads redone for enamal removal. I had wound T1 for Bob some weeks prior, but Bob had installed it.
Testing and Troubleshooting
First “power on” commencing the testing phase was on 20APR21. The QRP Labs Dummy Load was connected along with an earphone. All seemed to be good when initially powering up such as with the receive current draw. The first thing noticed though was nothing being heard in the earphones – not even a background hiss regardless of the volume setting. Something, or somethings, were amiss! More discovery was ahead!
JP7 and JP8 signals when starting the troubleshooting (outputs from IC5A (IC5.1) and IC5B (IC5.7) respectively) showing the I (channel 1, yellow) and Q (channel 2, blue) channels.
Found several issues in the I and Q channels including a missing capacitor and wrong value resistor. Should have caught both of these during the initial visual.
Troubleshooting the audio stages at JP11, IC8B (IC8.7), IC8A (IC8.1), IC9B (IC9.7), IC9A (IC9.1), IC10B (IC10.7) and IC10A (IC10.1).
Using my QRP Labs QLG1 GPS Receiver, Bob's QCX+ was “calibrated”. It did not seem to be “off” from 7.020 MHz very much, but performing the calibration with the QCX+ unit’s menu 8.11 “Cal ref osc” and 8.12 “Cal sys osc” calibration procedures got it “spot on”.
The 412 mVpp seen from the o'scope catpure was the initial RF output. This paltry signal output works out to be about 3.5 mW which is nowhere near the 4-5 W expected. There seemed to be something amiss with the transmit side. There was plenty of drive out of IC3A (IC3.3).
Upon closer inspection around the “finals” and supporting circuitry, R42 was found to be a 120 K ohm resistor (as shown above) instead of being 1.2 K ohm. Somehow, I missed the value difference when doing a visual compare of the schematic and parts list when first starting the project. The 120 K ohm resistor was deinstalled and replaced with the correct 1.2 K ohm resistor from the extra parts.
Amazing what changing out R42 from the wrongly installed 120 KW resistor with the correct 1.2 K ohm resistor. The output shot up from 412 mVpp to 41.2 Vpp after getting R42 exchanged. That 41.2 Vpp output voltage correlates with being right around 4.25 W.
Test setup showing around 4.3 W on the little Welz power meter (that I use when outside…have had the unit for probably 30+ years and still works great for quick checks) and at 41 Vpp on the o’scope.
Several issues were found fitting the assembled Display and Main boards into the enclosure. The first was the board-mounted 1/8-inch (3.5mm) phone jacks were each cocked slightly where they would line-up to enter the rear panels holes (as shown below). I also had to modify a nylon M3 nut by cutting off one side so that it fit next to the Volume control, R1, when the Display Board was fit to the enclosure’s front panel (not shown).
The pieces and parts ready for assembly after the checking out the QCX+ on the bench.
The QCX+’s Main Board showing the 1/8-inch (3.5mm) board-mounted jacks not lining-up for inserting through the enclosure’s rear panel holes (rear panel view). The jacks were then seen to be visibly not perpendicular or “cocked” to the right side of the Main Board (left side of the picture from this rear panel view).
The QCX+’s Main Board showing the 1/8 (3.5mm) board-mounted jacks after being desoldered, positioned correctly (now perpendicular to the Main Board), resoldered, and now aligning with being inserted in the enclosure’s rear panel holes.
All buttoned-up! Everything seemd to check-out. Bob's QCX+ 5W CWd Transceiver is ready for some use and fun on 40m!
The QRP Labs QCX+ 5W CW Transceiver - 40 m Kit -- Repair , Testing, Troublshooting, and Assembly is a PDF document with a more detailed account along with more pictures of the issues encountered with the kit and thier resolutions. The document can be viewed online or downloaded.