Hello, Yes, I have an idea what it is: one of 2 things---either one channel of the phono "pre-amp" stage is intermittent (possibly bad capacitor or solder joint) OR you have an intermittent /dirty input selector switch (the one that decides the input from tuner,aux/cd/tape/phono,etc) (assuming it is not the turntable) Buy a good quality contact cleaner and open up the unit and spray the switch in question. Check the area around the phono pre-amp stage and input jacks for bad solder joints and / or bad connections. I've been in the electronics service trade (audio in particular) for over 40 yrs. and am sure one of these will remedy the problem. It is NOT "anything" to do with protection whatsoever. Good Luck!---Kurt PS: have you tried swapping phono cables left to right--right to left to see if the problem "stays" with the same channel??

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