NAD Tuner 4220

[Bob]

I have a NAD tuner that is a little sick & could use some advice.
When I first turn it on, it will not lock on any stations when I use
the seek button. After ~5 minutes, the seek works on very strong
stations and after a little longer time, the seek works as intended.
Any ideas? It appears that Q106 2SC1815Y controls the sensitivity by
adjusting a 10K pot feeding the gate. Thanx!

 

[Mark D. Zacharias]

I have a NAD tuner that is a little sick & could use some advice.
When I first turn it on, it will not lock on any stations when I use
the seek button. After ~5 minutes, the seek works on very strong
stations and after a little longer time, the seek works as intended.
Any ideas? It appears that Q106 2SC1815Y controls the sensitivity by
adjusting a 10K pot feeding the gate. Thanx!

The discriminator needs adjustment. This is a very common problem in digital
tuners as they age.

There are two discriminator adjustments in a typical digital tuner. I can
never remember which is which (primary and secondary, that is). One adjusts
the station centering, which is your problem by the way, the other affects
the audio distortion more. For this reason, the adjustment should be done
according to the service manual.

There is usually a test point consisting of 2 posts, and one adjusts the
appropriate transformer for very close to zero volts DC across the terminals
when tuned to a station near 98 mhz.

In very rare cases an out-of-spec 7.2 mhz crystal could cause this problem
also.


Mark Z.