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Kenwood TS-680S power switch repair

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Old 08-14-2011, 11:04 AM
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Default Kenwood TS-680S power switch repair


( Repair notes provided by
KB0HAE)

I recently turned on my TS-680S and got very odd results. It had been working normally. But this time I got an odd squeal, and all the display digits were dim and displaying an 8 for all digits including the memory and RIT digits. I shut the radio off right away. I immediately suspected a low voltage condition. I checked the radio controls, and then measured the power supply voltage. The supply is an Astron SS-25, and the voltage was 13.8vdc. I connected my float charged battery to the TS-680S and got the same results. I connected the SS-25 to my TS-430S, and it worked normally. My next thought was to check the power switch in the TS-680S. It is a double pole single throw push on-push off switch. One set of contacts activates a relay that powers on the radio, the other set turns on the meter light bulb.

After taking the covers off of the radio, swinging down the front panel and taking readings at the switch, I found the the front section was bad. While there was no resistance across the switch contacts, there was 13.8vdc coming into the switch, but only 4.5 volts on the other contact. I noticed a watt resister connected between the two top switch sections. This was there to drop the voltage slightly to the meter light. There was a white wire on the top front switch section, and a red wire on the bottom front switch section. The red wire is power coming in, and the white wire goes to the relay mentioned above. At this point I disconnected the power cord from the back of the radio.

As the front section of the switch was bad, I decided to use the back section to turn on both the radio and the meter light. This involved de-soldering the two wires and one end of the resister from the front switch contacts, and the wire to the meter light from the bottom rear contact. I bent the resister away from the switch and soldered the meter bulb wire to its free end, insulating the connection with heatshrink tubing. Then I soldered the white wire to the top rear contact, and the red wire to the bottom rear contact. After inspecting my work carefully, I plugged the power cord back into the radio.

I swung the front panel back into place, and turned on the radio. It now works normally again. I originally had read that the TS-430S sometimes had the same problem, and the same fix. I did decide to order a new power switch. It was listed as available from Pacific Coast Parts. I wanted to get one while they were still available just in case. I guess the switch is not available anymore.

I re-assembled the radio and made some test transmissions into a dummy load. My TS-680S now works as it should again. This not a difficult repair. I wish that I had thought to take before and after pictures.

As with all such modification, perform this repair at your own risk. I will take no responsibility if you damage your radio, or hurt yourself. Please do not work on your radio with the power cord plugged in. Also think carefully about what you are doing and be careful not to hurt yourself.


73
Jeff
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