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NAD tuner repair

blackscorpio

Active Member
Joined
May 16, 2012
Messages
437
Points
43
Location
Hyderabad
Dear members,

I bought a NAD 402 from UK (which I couldn't test there as non availability of other equipment), due to reception issues, I wasn't getting any channels except 106 something. At first I didn't had any idea it was because of bad reception, I guessed it wasn't working, so gave it to a local repair guy & he messed up a little rest I did;).

Now its not picking up anything, I guess I messed with some tuning pots on the PCB inside.

so, where can I get it fixed? Anyone local in Hyderabad will be helpful. I am open to courier it for repair service. Please help me.

Thank you
 
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reubensm

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May 26, 2010
Messages
4,643
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113
Location
Trivandrum, India
Sorry to hear about the tuner. Can you outline what all was done to it, what all was changed? Was it only trimmers, IF transformers and other adjustments only or where there any components changed/replaced or any modifications?
 

blackscorpio

Active Member
Joined
May 16, 2012
Messages
437
Points
43
Location
Hyderabad
just only the trimmers(I guess these are those pots like you tune with a screw driver turning), there were 3 of them, I will post a pic asap. Nothing else was touched.
 

reubensm

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Location
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One has to have equipment like a signal generator, oscilloscope, and other RF test equipment, I believe to handle calibration. In the early days when AM tuners used to be very simple, there dial chords turning a gang (tuning capacitor) and generally 3 silicon transistor stages coupled with 3 adjustable IF transformers. There were a set of Antenna coils and Oscillator coils for each band. These are the types of radios that one could tune up even if one did not have a signal generator. The trick was to tune to a weak station, and carefully adjust the IFTs going from 3 to 1. The oscillator coils and were fine tuned to move the station slightly to the left or right on the dial. The antenna coil and trimmers were calibrated in similar fashion. For MW, the antenna coil would be moved about on the ferrite rod, till the best reception was achieved.

With modern receivers like the NAD, one cannot do this. Indian service centers are generally manned by personnel who work out of experience and are obviously not professionally trained to work on specific branded equipment like NAD. I have noticed this with NAD amplifiers as well. These folk are likely to escalate the issue or create new ones while working on NAD equipment. When choosing a technician for repairing a NAD, the first question should be - do you have experience with NAD and how many have you serviced. If the answer is, never seen this before, stay away :)
 

blackscorpio

Active Member
Joined
May 16, 2012
Messages
437
Points
43
Location
Hyderabad
When choosing a technician for repairing a NAD, the first question should be - do you have experience with NAD and how many have you serviced. If the answer is, never seen this before, stay away :)
Yes I should have not done what I did but I got frustrated. I had it for more than a year now & I tried all I could, bought some dipole antennas but it wasn't working so I concluded it is dead & want to try my luck before giving it to a technician.:)
 
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blackscorpio

Active Member
Joined
May 16, 2012
Messages
437
Points
43
Location
Hyderabad
Yesterday I took out to take some photos, in the process I connected it to my audio system & surprise, it is working. I was able to tune 10 FM stations.

:cool::cool::cool:

Today morning I sent the pics, marked with all trimmers that are messed with, to Omishra. Just it so happens, they are AM related, so only AM is messed up.
 

omishra

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May 31, 2011
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Pune
Sorry for the confusion with AM IFTs which I clarified to the member. Later I checked with the service manual. Those coils where input and output filters of FM stereo detector to cutoff HF harmonics to reduce audio distortion. Nothing audible effect! His problem was poor reception and auto muting in stereo mode. Hopefully it will get resolved with front panel "mono" switch.
 

blackscorpio

Active Member
Joined
May 16, 2012
Messages
437
Points
43
Location
Hyderabad
Sorry for the confusion with AM IFTs which I clarified to the member. Later I checked with the service manual. Those coils where input and output filters of FM stereo detector to cutoff HF harmonics to reduce audio distortion. Nothing audible effect! His problem was poor reception and auto muting in stereo mode. Hopefully it will get resolved with front panel "mono" switch.
Thank you so much for the clarification.

It just so happens, while you were sending this message, I am checking the tuner. I had to put into the rack so I had to run the cables properly. Just now I am back & happy to report that everything is working fine. The channel I reported not getting audio is fine now. Looks like everything FM fine. Still I need to test the AM part.

For the reception, I had to lay down a dipole antenna on the terrace above 5th floor, from there I used old 75ohm DTH cable into my home, I used a 300ohm to 75ohm balun to connect dipole antenna to DTH cable. Reception is very good & FM is very clear.

Now I need to find a good connector to permanently connect the antenna to the tuner. I couldn't find a proper connector(see the connector on the tuner), the middle pole is too narrow. Any ideas would be appreciated.

connector.JPG
 
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