Saturday, August 11, 2012

First KX3 mod

I carried out my first modification to the KX3 - or rather to the KXPD3 paddle. It was the mod to solve the missing dah problem. I hadn't experienced it, but it was one of those issues that would rear its head at the most inconvenient opportunity so I decided to do the mod. This involved disassembling the KXPD3, cutting one track and bridging two pins on the key's circuit board.

The KXPD3 came apart easily, in fact rather too easily as it disintegrated into its component parts before I had a chance to see how it went together. That's the trouble with taking apart something that has a spring in it!

I then cut the track indicated and bridged from one pin to the adjoining track. Why is it so difficult to make a solder bridge when you actually want to.

I reassembled the KXPD3. Before I did I dismantled a couple of 409Shop complimentary ball point pens to see if they would provide an alternative spring for the paddle. They did, but they didn't seem to be weaker than the original (the only way to alter the tension with this key is to change the spring) so I reassembled using the original.

After that I connected the KX3 up to a dummy load to try out the modified key and confirm that I hadn't broken it. The key still worked, and my sending was still as bad as it was before, so all was as expected.

I hade a tune around on 40m and heard one of the special even stationsfor the Olympics, 2O12L. He was loud enough to be an easy contact with the QRP KX3 - but I was getting no transmit output! Eventually I switched to the K3 and worked 2O12L followed in quick succession by the Welsh Olympic special event station 2O12W.
After I had completed the cotacts I switched back to the KX3 to find out why I was getting no SSB output. I found that VOX was working, the rig was switching to transmit, but I was still getting no output.

Eventually aftter much tearing of hair and playing with settings I discovered the reason for the problem. I had turned the power down to 0.0W when I was testing the keyer...

Words fail me.


VE3WDM said...

Good morning Julian, I had a smile on my face as I read your post.....I had come against and done things you had described in our post. Just the other day I had to make a solder bridge. It was for my Qrpometer from the 4stateqrp kits. In the building of my K2 solder bridges seem to be easy to come by.....but could I do one when I had to NO!!! I kept ending up with 2 separate blobs of solder. The only progress that I seem to make was lager blobs of solder. With my K3 I did the mod for adding the P3 with the SVGA card installed. The K3 would shut down on overload but there was a mod for that. I did the mod an then tested the rig. There was no output. My worst dream seemed to come true.....I screwed up my K3!!! After about 45 minutes I realized my rig was in test mode which does not allow the rig to transmit. It was time to shower after having worked up a HUGE sweat.

Eldon R. Brown SR said...


There is a trick (as you know) to obtain the normally desired smooth solder joints, and that is the use of flux.

And, the opposite is ALSO true for making solder bridges. After tinning the pads with a little excess solder, remove the flux and allow the solder to oxidize a bit by melting the solder with a dry iron. Then you can drag the solder where every you want (or not). In other words, use the un-learned techniques of your younger years and your first experiments that typically produced cold solder joints.

It works for me.

Julian it is good to hear and see you working on things !

Eldon - WA0UWH