Faulty NAD 4100 Tuner - help & suggestions needed
I purchased this tuner for next to nothing in a faulty condition as a repair project, for something to tinker with, and maybe to learn a little while I'm at it. The price paid was extremely low, so I can't justify spending much on it. The AM section is fine, but FM is not so good. It will seek and find stations with little more than a short wire attached to the aerial terminals, which suggests to me that the front end is OK. However it will only go into stereo on very strong signals, even when fed from my rooftop aerial. Mono reception is clear but very faint, but when it does go into stereo you get a what I can best describe as a 'Dalek' effect on human voice.
Inside I can see a LA3401 stereo demodulator IC, which, in view of the above symtoms, is the obvious thing to replace. I see from the datasheet that this device remains in circuit for AM reception, and since this part of the unit still works I guess the 3401 can't be totally dead. Before I adopt the highly un-scientific approach of just changing the IC, can anyone suggest a few basic checks I could do, to prove the health or otherwise of this device? I have a DMM, and can borrow an oscilloscope if that would help to make a diagnosis.