NAD 7020 tuner problem

[aviv_zl]

Dear all,

The original problem was that my NAD 7020 tuner could not receive FM stereo (mono is OK). To start with, I went into the alignment procedure of the FM tuner according to the service manual. While trying to align the tuner, I think it was while I turned the detector coil when suddanly the tuning indicator LED's got stuck on the right arrow, centring LED will not illuminate anymore at all and the FM muting is always on. Although the tuning arrows and the centring LED's will not function anymore, I can still tune in radio stations and receive them fairly (mono only).

I took the threaded ferrite core out of the coil (there are two, one internal and one on top of the coil), to make sure it's not broken. A little piece (sub mm) was chipped at the top of the upper ferrite from the screwdriver. I have to admit that I was stupid and used a metal Allen key (virtually not magnetized). Anyway, the two ferrite cores seem to be OK.

I wonder if someone is familiar with this tuner and could advise how to diagnose the problem.

Thanks in advance.

[Techman]

It's a bit late to say it now, but the rule is always the same - if a fault suddenly appears, and if nothing else has been touched, a 'component' has obviously gone faulty, so the last thing you should be doing is to start touching the alignment. What you've done is going to make it difficult, or possibly impossible to find the original fault. However, fingers crossed for you that someone with experience of this tuner will be able to step forward with suggestions.

[stevehertz]

I have had to change a few stereo decoder chips when repairing and restoring 70s and 80s tuners in recent years. I realise it's a stab in the dark approach but they're not expensive as I recall. Best of luck.

[aviv_zl]

Thanks. I already ordered replacement chips to give it a try. However my main suspicion is the detector tunable coil, as during turning it, the tuning LED's stoped functioning correctly.