KilgoreCemetery
- Apr 12, 2017
- 258
- Joined
- Apr 12, 2017
- Messages
- 258
Everything on this receiver works great except for one little thing. The FM Muting cuts out to the beat of the music or when commercials get too loud. It's not dependent on the actual decibel rating coming out of the speakers, just the incoming FM signal. Like, if it's a quiet song or a mono signal, I can crank the volume knob up as high as I want and it never cuts out. It only does it with a strong FM Stereo signal.
My understanding is that the FM Muting sensor is supposed to filter out the audio and sample the signal strength somehow. From the way its acting, I would say the audio is not getting filtered out. I can't find any more information than that about how it's supposed to work, so please correct me if I'm wrong.
I pulled up a schematic for this model and found that the FM Muting adjustment is right next to an IC (NEC C1167C2), but I can't find a datasheet for it. I did learn that if I touch or wiggle the coil (L102), the signal cuts out completely.
I tried adjusting the Muting with VR101, but it didn't help, so I put it back to where it was.
I checked voltages on the IC. The only pins that were way out of spec are:
15: fluctuates between 1.2V - 2.8V quickly
13: 3.5V
12: -290mV
I don't quite know where to go from here. Is it probable that the IC has a short? Does the IC do the audio filtering? Is there some place I can read up on how FM Muting is supposed to work?
My understanding is that the FM Muting sensor is supposed to filter out the audio and sample the signal strength somehow. From the way its acting, I would say the audio is not getting filtered out. I can't find any more information than that about how it's supposed to work, so please correct me if I'm wrong.
I pulled up a schematic for this model and found that the FM Muting adjustment is right next to an IC (NEC C1167C2), but I can't find a datasheet for it. I did learn that if I touch or wiggle the coil (L102), the signal cuts out completely.
I tried adjusting the Muting with VR101, but it didn't help, so I put it back to where it was.
I checked voltages on the IC. The only pins that were way out of spec are:
15: fluctuates between 1.2V - 2.8V quickly
13: 3.5V
12: -290mV
I don't quite know where to go from here. Is it probable that the IC has a short? Does the IC do the audio filtering? Is there some place I can read up on how FM Muting is supposed to work?