My Elecraft K2

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A ham radio friend Art, VE1EP, who had been active in ham radio for many years, built this Elecraft K2 from a kit when he was 87. He used it for three years before health reasons forced him to give up ham radio. In 2006, when he could no longer use the K2, he gave it to me. Click on the photo to see a larger view.

Asymmetric filters

The K2 has two CW modes: Normal CW and Reverse CW. These reflect the use of a positive or a negative offset to produce the sidetone when setting the VCO frequency. Each mode has a set of four variable-bandwidth crystal filters for use in isolating a CW contact from adjacent signals. I noticed that the effect of these filters is not the same between the two modes; the Reverse CW filters seemed to work correctly but the Normal CW filters do not seem to progressively narrow the bandwidth. I subsequently found a reference on the Web that says altering the sidetone frequency, which the K2 software allows, requires the filters to be realigned. Not knowing this, I had changed the sidetone frequency without recording the original setting. Thus I may have caused the problem while having no note of the original sidetone frequency to return to.

Perhaps relevant to this, I found that the band memories that had been set by Art all brought up Reverse CW mode. Thus it’s possible that Art also had this problem and therefore used Reverse CW with its correctly working filters. Since the Reverse CW filters appear to work O.K., I left this problem for later. The manual describes a method of setting the filters and that is what I will do.

Broken headphone jack

After using the K2 for a couple of weeks I had a problem with the headphone jack. One day I plugged in the headphones and got no audio from headphones or speaker. Jiggling the plug brought back the audio but I found that the jack on the K2 was very loose. I assumed that it had come adrift from the printed circuit board. A Google search showed that the K2’s headphone jack frequently fails. One is advised to avoid frequently plugging and unplugging headphones; some articles go so far as to suggest a K2 modification by adding a switch to choose loudspeaker or headphones, leaving the headphones permanently plugged in. One is also advised to use a standard 3.5 mm plug, preferably with a right-angle bend, so as to avoid stressing the jack with the weight of a heavier plug. I had bought a new pair of SONY MDR7509HD headphones which have a combination 3.5 mm and 1/4” plug that is heavier than a regular 3.5 mm plug, so this was probably the cause.

I decided to open the K2 and re-solder the jack. I expected it to be a bit of a hassle to get at the jack but I was surprised and quite impressed with the ease of disassembly. After removing a number of screws that hold the case together, and two screws that secure the control board to the front panel, the K2 disassembled into four main parts, all of which plug into each other. I didn’t have to unsolder a single wire. On the right is a photo of the disassembled K2. Click on the photo to see a larger version.

Having disassembled the K2, I took a look at the headphone jack. As I said, I thought that the jack had become unsoldered from the board but this turned out not to be the case - the solder joints were as good as new. Instead, I found that the plastic case of the jack had broken which allowed the metal parts to become loose and point off to left field. Its difficult to see in the small photo on the left but if you click on the photo you can see a larger version together with details of my fix which involved enclosing the jack in a piece of heat-shrink tubing. The fix worked and the headphone jack is now working O.K.

When giving me the K2, Art gave me the bits he had left over from the kit. It’s interesting that among the leftovers are two spare headphone jacks since Elecraft sent him three jacks with the K2 kit.

No audio combined with full-scale S-meter

After experiencing the broken headphone jack and before fixing it, I encountered another problem: when pressing any of the front-panel buttons the audio would cut out and the S-meter would go full scale. It would stay this way for a while before gradually returning to normal operations over a period of a second or two. Subsequently I discovered that tapping the case caused the same problem; sometimes just touching it was enough. Also, a light tap in a particular direction sometimes restored operation. I assumed that something was loose inside.

When I took off the top of the case in the process of fixing the headphone jack, I was able to probe for loose connections with the radio running. I found that a slight pressure on the control board would invoke the problem. I inspected the solder joints of the connectors on the RF board where the controller board and front panel plug in and re-soldered a couple of solder joints that did not look pristine. However, putting the K2 together again showed that not only was the problem not fixed, it was now a permanent condition!

Searching the Web, I found a couple of references to this problem encountered by people in the process of building their K2’s. It seems that the audio is muted by the mute line unless it supplies the proper signal. Also, the 8R line can also be involved in muting the audio.

Back to the K2, I wondered if removing the two screws that secure the control board to the front panel would let me flex the control board a little more freely to see if that would bring back the audio. So I removed the two screws, turned on the K2 and, without even flexing the control board, found that the problem had gone away. To cut the story short, I found that inserting and tightening the screw that is next to C15 caused the problem to appear. I removed the control board and looked for bad solder joints around the area of the screw. I didn’t find anything significant but noticed that, not far away, the solder on Pin 1 of J1 looked a little scanty. Looking at the circuit diagram I saw that this was the 8R line, one that had been mentioned in the posts! I re-soldered the pin, reassembled the K2 and turned it on. It worked fine. I replaced the two screws holding the control board to the front panel and tightened them. The problem is fixed!


My Elecraft K2

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