Kenwood TS-930S/AT maintenance

Mode switch failure

In July 2017 a terrible mishap put my TS-930S out of operation. I usually work in CW, and use the mode switch to alternate between the CW and the TUNE settings. On that particular day in july, I attempted to use the TS-930S for SSTV operation, and had it hooked up to the sound card of a personal computer.

To put the TS-930S into FSK mode, the mode switch needs to be turned to the rightmost end of the scale. I noticed some mechanical resistance, but turned the switch anyway, when all of a sudden the rig showed failure symptoms: RX sounded strange, and it would no longer transmit, nor tune.

Since I was at the same time playing with my Yaesu FT-950 on 6m, I first thought that my 6m transmission had killed the receiver. I first looked for help on eham, where my hypothesis of receiver overload was quickly ruled out. I then opened to 930S for inspection, and discovered (to my dismay) that the mode switch on the front panel actuates the actual mode switch via a mechanical pull.

Disassembly of the push/pull mechanism revealed that the perforated metal band inside the plastic guide was torn apart, and repair impossible.

I then had a look at the schematics to see if a workaround was possible. I really only need to toggle between CW and TUNE mode, so maybe a clever relay mechanism would allow me to do just that. The schematics show that that's indeed possible - the mode switch is a four layer switch with 6 positions, but only S10-1 changes between CW and TUNE, as can be seen upon clicking on the image below.

While I was studying the mechanical possibilities to perform this modification, a band switch mechanism for the 930 showed up on ebay, and I secured the deal and arranged for pick-up on my next trip to the States (shipping and duty exceeding the value of the switch). I would be curious to know if fellow hams have found a solution to repair this failure.