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The FT-840 uses a die-cast RF power amp
with thermally switched fan to ensure full power output (up to 100
watts). The digitally synthesized local signals ensure clean, low-noise
transmitter output on all HF amateur band. There might be no AC line interference. it has strong Rf output. any AC line intersect does not affect its radio performance. Check and adjust RF power so to maintain proper output. some times more RF power generated at the output may cause interference. adjust Rf power..Even some unfiltered Noise getting the other end of the end may calso cause interference. Check for any Ripple voltages present at the output. Contact authorised service station for further Rectification. thank you shanth
You have to ADD a PL Tone board. There should be a front panel switch that says TS that is the on/off power to the connector. There is a connector inside for +12VDC, switched ground and Encoder input. Look online for the schematic, or contact CommSpecialists for the sheet that lists the colors of the wires on the connector and where you connect them when you add a CTCSS Tone board.73's
I experienced very similar or the same problem with FT-840. When power is inceased over about 50 W, an AM on RF signal arises. Even when TCVR is supplied from accu and connected to dummy load. Period of interferencing signal is about 7.5 ms (130 Hz), so it cannot be hum from mains. I have not opened the PA block yet but i guess, it could be caused by damaged capacitor(s). Jiri