Audio Systems: Nakamichi Receiver Tuner Section No Output, amplifier output, rca connector

Question
In my home I have a Nakamichi TA-4A receiver, circa 1990, which has been working beautifully until yesterday, when the tuner section abruptly stopped working, along with the tuner's front LCD display (which shows channel, FM/AM, signal strength, stereo lock... Those things related only to the tuner section's function). All other switches outside the tuner's LCD display illuminate as normal and all other input and output functions of the receiver in general seem to be working correctly. The display is not entirely dead. If I push the FM or AM selector buttons there is a brief flash of the appropriate signal type, either "FM" or AM" and the abbreviation for megahertz (MHz). If I push the FM or AM selector button, channel selection buttons, or up/down scan buttons, I hear the switch's electronic "click", for lack of a better term, as a slight feedback through the speakers, indicating to me that there is amplifier output available on the tuner power board. But something is keeping the tuner from switching fully on and the display from fully operating. There's only one thing I can think of that might have caused this problem. I believe that a self-powered, accessory FM receiver may inadvertently have been plugged into the output ("Record") side RCA connector of the Nakamichi's tape monitor #1, by a confused family member, while the FM tuner of the Nakamichi was switched on, immediately before this failure took place. That's the only clue I have as to anything that might have caused the problem. I pulled the cover off of the receiver and checked all fuses. None have failed. Can you give me any idea what may have happened, or anything that I might do to help diagnose the problem(s)? I have the factory schematic and parts breakdown at hand, as well as a VOM if needed. I love the receiver, plan to keep it and have it repaired as necessary. But I'd like to not go into the repair process without some idea of the nature of the problem. Any assistance you can provide will be sincerely appreciated. Thanks.

Answer
Difficult to say without some hands-on examination.

My first guess would be the voltage regulator in the main power supply that feeds the tuner section has failed.  Could be a transistor, diode, zener, shorted electrolytic capacitor, etc.

I think you should have an audio shop take a look at it.  Chances are it is not an expensive repair.  If you have a vom or voltmeter and know how to take basic voltage tests you may be able to identify the failure point but unless you have some electronic skill better leave it to the professionals.  

This kind of repair is one step above the home DIY project level.