Input selector knob not working (Kenwood KR-5030)

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I recently bought a Kenwood KR-5030 receiver off ebay and shortly after play the input selector knob ceased to change the audio input. The FM indicator remains lit and the sound source does not change even after turning the knob to Phono or Aux. Any guesses as to why this happened and if there are any suggested fixes before I potentially exchange this product.

To give you a bit more of an understanding of my situation, I had a turntable plugged in and was listening out of the headphone jack on the Kenwood unit. Speakers or other devices were not hooked up.
 

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If the switch action is clicking as you rotate it, yet still not changing or at least turning the tuner off, the switch wafer(s) are damaged. If there is no click action either, the shaft and/or knob connection is slipping/damaged. It's a custom made mechanical switch (Sg1) with multi-wafer construction and many different switch sub-sections to simultaneously switch the lamps, inputs, phono preamps, meters etc. for both channels. They are in every old receiver but will be uniquely constructed for the particular model series, so likely irreplaceable.

Early amplifier/receivers had a mass of hand wired switch connections that need to be removed, identified and refitted, making switch replacement a very tedious and expensive job. Still, it may be repairable without removal if you are patient and handy with repairing small mechanical gadgets.

There are also Ic lamp drivers ICg 1-3 etc that also mute and do the actual switching of associated circuits, so this would require more investigation too. As you say the switch worked for a while, perhaps someone has already attempted a fix but didn't do it properly. That could make matters worse but any evidence of this could give you a clue to the location of the problem.
 
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Thank you for the very thorough response, Ian Finch! It does click when turned, but alas the input does not change. Perhaps it is due to damaged switch wafers, as you've said. I'm not very handy in mechanical and electrical tinkering, so I'll see what the seller has to say. Thanks again!
 
Just one dumb question; are you using an input that bypasses the input selector, like using a "Tape Monitor" switch that selects either A or B tape playback input?
This also blocks input from the other sources giving an impression the rotary switch doesn't work but may not be your issue.
 
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