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.

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.

Weiterlesen

Advertisements

KX3 encoder issue

While operating on DM/BW-852 I encountered an issue with the Keyer/Mic- encoder of my KX3. For about a minute it wasn’t possible to change the keyer speed. Luckily the speed was set to a reasonable value (20 wpm). Then, maybe by touching the knob differently, it worked again.
A couple days ago, when preparing the activation, I had the same issue while trying to reduce the KX3’s output power. I pushed the button (the display showed 10 W) and turned the knob. The reading went down to 9.8 and stayed there regardless of any further turning. I switched to „keyer speed“ by pushing the knob (which actually worked) and tried to change the keyer speed to no avail. Then I switched back to output power and turned the knob again: the encoder did not work. Even after switching the KX3 off an on, it remained in this state.

Next I opened the KX3, took out the CP- board and did some resistance measurements at the back side of [Z4]. Now the encoder seemed to be working again. After assembling the KX3 everything worked smoothly.

It looks like the encoder has an issue. But before I replace it (or even all four of them) I asked the experts at ELECRAFT for a confirmation. The reply arrived within a few hors (!)

„Hi Roman,
Thanks for the contact.  To your questions on the KX3 encoders, we have received reports of some encoders losing some of the damping fluid that is embedded into the shaft and sleeve.  These are sealed but can leak.  When this happens, some of the fluid will get into the optical encoders and cause the symptoms you are seeing.
Generally, we recommend all 4 be replaced at the same time to save having to do them individually.  We do this with the K3 and K3S encoders in much the same way.
The KX3 encoder is Elecraft part #E640018 at $2.08 each.“

The encoders are already ordered and will be replaced as time permits. Thanks ELECRAFT for the fast support!

KX3 Go Box

Having played with the KX3 for a couple of weeks I wanted to try it outdoor. But Hiking comprises some risk for the rig: rain and snow, shock and vibration and scratches from other things in the rucksack. The first attempt with bubble wrap worked but was not to my full satisfaction. A box was needed!

I searched the web for availalbe solutions (which are quite a few) and found Tom’s great Go Box:  http://www.oe2atn.at/tom/gobox/ – the most professional one I found.

However, I had something different in mind: The box should look understated in order not to attract thieves on a long hike or a stay on a camping site. By accident I tripped over an empty first aid box. Slightly too big for the KX3 but apart from that very nice.

[edit]: From time to time, while turning the dial, I noticed that VFO A seems to get stuck at a certain position. The frequency reading in the display „jumps“ back several 10 Hertz then moves on again and „jumps“ back. This can happen several times. Suddenly the failure disappears and the VFO works as intended.
This video from KC9W describes exactly my situation: https://www.youtube.com/watch?v=COPj2skxWys

One explanation was that the old version of encoder has been used inside my KX3. But taking a close look revealed that it is already the new version. (Link to ELECRAFT’s KX3 VFO Encoder FAQ)
Other possible explanations for this weird behaviour include excessive mechanical stress to the encoder.

When opening the Go Box, I found that the VFO A knob has left a mark in the foam in the lid. Possibly, under such pressure, the foam is no longer able to absorb external shock. Instead, pressure applied to the lid will be transferred directly to the VFO A knob and the encoder.
As a counter measure I removed the foam from the lid (as can be seen in the picture below). Now there is some space between lid and VFO A knob even if the lid is closed. Instead, I put a large piece of foam on top of the bezel. If the lid is closed the foam will be compressed and keeps the KX3 in its place. But it no longer applies any pressure to the VFO A knob. If this temporary solutions works, I’ll have to think about something more professional…

go-box