Need digital tuner expert

audiomaniac2

Active Member
I'm working on a NAD 7140 that has a defective tuner. Unfortunatly I hav'nt found a schematic with voltages listed on it. The tuner will scan but never pick up a station. Test point 102 voltage never changes as it scans stations. Dual op amp (feeds tp- 102)
ic112 (upc4558) has the following voltages on it's pins.All voltages a positive to chassis ground.
1- 1.31 volts
2-4.99
3-3.07
4-0
5-3.07
6-5
7-1.3
8-34
The big tc9147p chip drives this chip. Any Ideas?
 
Check out this thread on the 7130 that had trouble locking on a station. http://www.audiokarma.org/forums/index.php?threads/nad-7130-tuner-section.798012/ See if it helps. Both SM's on HiFIEngine.com.
Thanks for responding.
Check out this thread on the 7130 that had trouble locking on a station. http://www.audiokarma.org/forums/index.php?threads/nad-7130-tuner-section.798012/ See if it helps. Both SM's on HiFIEngine.com.
Thanks for the info. Unfortunately the tuner in the 7130 and 7140 are different and neither schematic has any voltages on it except for the power supply.
I get no reception at all but the digital display will scan or manually move. on test point 102 the voltage should increase as the stations goes from 88 to 108 mhz (it doe'snt) according to the service manual. Makes me think ic112 may be defective, or ic110. Could be something else . Without having the voltages it makes it way harder.
 
You can often find data sheets for each of the main chips in the tuner (FM-IF, PLL synthesizer, and MPX decoder) that will show what voltages to expect.

You might consider having this thread moved to the Tuners section.
 
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