12 August 2016

Kenwood TS-440 keyboard repair.

I'm using the Kenwood TS-440 as my MF station. The reception is excellent on MF and what's more the noise blanker seemed to behave superb on the MF frequency. But the TS-440 has it shortcomings in a mechanical way. The front keypad was not designed for over 30 years intensive use. The copper clickers inside will wear out. In my case some buttons didn't react anymore. But because using the memory facility it was not imminent.
But on certain moment it becomes annoying. asking for a solution. In the past I did already several clean actions based internet information like this Kenwood- ts-440s-keypad-bounce-fix
BTW: You can use this link in a How-to disassemble the keypad..

Well being in 2016 there are now cheap switches available which fit into the place of the old copper clickers. On AliExpress I found these Aliexpress-Push-Button-Tactile-Switch-Momentary-Tact-4x4x1-7mm-4pin-SMD
View pricing for 100 pcs (for 4 sets TS-440!) I ordered a pack which arrived within 10 working days.

In case you reading this and the Ali link doesn't work anymore a picture and technical specs.:

Suggested searchkeywords: Push Button Momentary Tact switch 4x4x1.5mm 4pin SMD

4x4mm is the footprint of the switch (almost the same as the TS440) and 1,5mm is the height. Which is to high , see later.

If you don't know how to disassemble the keyboard zie link above! (keybounce fix)

The main effort is to fit the switches on the board. You have to remove some PCB lines and arrange some new "lines". For "removing" I suggest to use the same method Kenwood did, just drill a small hole. Advantage is that you can make connections thru the back with thin wire. (I used wrap wire diam 0,25mm)
You understand already that for each switch you have to look for an solution. If you have experience with electronic DIY projects, you will soon see the algorithm in the circuit.
It's a bit difficult to explain in words here, but believe me, you soon see the "system".

If you look at the photo of the switch, the swithing takes place between the horizontal connections. In some cases you can use this feature to "bridge" connections.

There are 25 switches to do.
Some are easy, some difficult (at least 2 on the left keyboard "6"& "0")
Start with the right keyboard (RIT XIT A/B SPLIT ect) these are rather easy. Best is to commence with the "1MHZ" button.
You can test directly during the assembly with the TS-440 by plugging in the connectors.
Do observe the  "F.LOCK" switch. If engaged some buttons are disabled.
Don't test it everytime, because it will wore out the connector in due time.
A meter with a "buzzer" is also OK for making the check.

You can solder with a "normal small" solder iron. Start to tin one corner. Make sure that the corner is easy accessable for you. Depends if you are left or righthanded. Place the switch on its wanted location, melt the tinned corner and move the switch in such that that is precisely in the middle. The switches I used, the feet were just to the edges, so adjusting was not so difficult. When in place, tin the other 3 corners.

As pointed out above, the switches are too high, but if you remove the pin on the plastic push key it will be just right. I used a "Dremel" tool to remove them. Do check this by the first button. Maybe you have a version which is different.
The whole operation took me 6 hours, inclusive the learning curve and coffee break.


Some more pimping... 

Replace the scalelamps by "clear led". I took 2 in series with a resistor.

Unstable frequency?
The TS-440 8Mhz crystal is just in the airflow of the fan of the PA.
This will result in a dramaticly change in temperature in the unit. WSPR transmission on higher HF bands will show a banana style trace when transmitting and after transmitting the received stations are likely to be off frequency a few Hz. Just cover the crystal with polysterene plastic. This will stabilize the short term temperature change in the unit.