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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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NAD Tuner 4220
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! |
#2
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NAD Tuner 4220
Bob wrote:
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. |
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