Replacing one of the KX3’s encoders

While operating on DM/BW-852 I encountered an issue with the Keyer/Mic- encoder of my KX3. A detailed description can be found here: Link

Elecraft support confirmed the encoder being the root cause :

„We […] do know that extreme temperature changes, more typically found with the KX2 and KX3, may cause shorter life spans for them.
The most common failure mode we see with the encoders is that the viscous damping material used in the shafts will leak out onto the encoder itself, which in turn, causes them to fail or skip as the encoder is turned.

Just one week after my first email to Elecraft support, the spare encoders arrived.
As they are not expensive ($ 2.08 each), the initial plan was to replace all four encoders at once.

Before I actually started,  I prepared my work space with an anti-static mat and wristband. It helps avoiding damage to the semiconductor devices due to electrostatic discharge.

Then I started disassembling the KX3:

Step 1: Remove the four Thumb Screws, separate the KX3 top and bottom covers and unplug the battery cable and the flex cable on the CP board (that’s the one where the display is).
Step 2: Disconnect the speaker [J7 – white] and remove the MIC connector from the side panel. Next, remove the battery retainer (2 screws). The top cover should look as shown above.
Step 3: Turn over the top cover. Remove all five knobs and the hex nut with lock washer from the VFO A encoder. Next remove the bezel (5 screws). The CP board should come loose now.
Step 4: Remove the left side panel (2 screws).
Step 5: The CP board can now be removed from the top cover. Put it carefully on an anti-static mat.
Step 6: Turn the CP board over and remove the VFO A- encoder PCB, sitting piggyback on the CP board [J6]. Now, locate the defective encoder on the CP board (in my case [Z4]).
Step7: Carefully cut all accessible pins of the defective device. This will make desoldering easier. Desolder the remaining pins and remove the defective encoder. Finally, clean all holes where pins have been desoldered. Repeat Step 7 or start assembling the new device(s).
Old and new encoder are looking exactly the same. I had doubts whether the new device could have the seam weakness as its predecessor and the issue could occur again. But according to Elecraft support the encoders have been improved during the years, resulting in improved reliability.

Be sure not to overheat the encoder while soldering. According to the experts extreme temperature changes are supposed to be the  reason why the viscous damping material will leak out onto the encoder.
Once soldering is complete, use pressurised air to remove residues from soldering.

For assembly just follow the steps in the opposite direction. When putting the knobs on the four encoders, make sure to support the PCB from below. The applied force may cause damage to the PCB or components soldered to it.

Despite my initial plan to replace all four encoders at once, I did only the defective one. Desoldering was tricky and would have been really difficult for at least one of the remaining encoders. So I decided to wait until the next encoder fails – hopefully not on a summit 😉

Edit: Scott, N9AA, suggested to use Chip Quik (which I haven’t heard of before) for desoldering the encoders. It reduces the melting point of the solder significantly and is usually used for desoldering large IC’s. There are some videos on YouTube. I haven’t tried it so far but I’ll post it here once I tried it.

3 Gedanken zu “Replacing one of the KX3’s encoders

  1. chaplinhugo 7. Dezember 2019 / 04:56

    Do you have exact part number (Bourn pec12rXXXXXX)?


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