Denon 3313CI Distorted Audio FL+FR

[ajvpb]

Hi all,
Hobbyist repairman here so I've reached the end of my troubleshooting abilities. The audio out of the FL+FR speakers is very distorted and almost unintelligible. BUT! That only applies to digital audio; Analog plays through just fine. The distortion carries to headphones if those are plugged in with audio from a digital source. All other speaker channels play fine regardless of digital or analog.

Previous experience with similar distorted audio has been bad resistors on the amp output - Could bad smd resistors on the hdmi board cause the same problem? My understanding of digital is that it either works or it doesn't - so I'm currently out of my element.

I have an oscilloscope (but no experience using it) if anyone can point me in a direction to start.

Thanks!


https://www.manualslib.com/manual/16...-Avr-3312.html

[petehall347]

Re: Denon 3313CI Distorted Audio FL+FR

could be as simple as a poor connection on a connector .

[budwich]

Re: Denon 3313CI Distorted Audio FL+FR

Hi all,
Hobbyist repairman here so I've reached the end of my troubleshooting abilities. The audio out of the FL+FR speakers is very distorted and almost unintelligible. BUT! That only applies to digital audio; Analog plays through just fine. The distortion carries to headphones if those are plugged in with audio from a digital source. All other speaker channels play fine regardless of digital or analog.

Previous experience with similar distorted audio has been bad resistors on the amp output - Could bad smd resistors on the hdmi board cause the same problem? My understanding of digital is that it either works or it doesn't - so I'm currently out of my element.

I have an oscilloscope (but no experience using it) if anyone can point me in a direction to start.

Thanks!


https://www.manualslib.com/manual/16...-Avr-3312.html

when you say analog works ok... are you referring the "EXT" inputs or things like cd r/l, etc? It would appear that the "thing" of interest is ic471... maybe. Although it could be earlier in the signal path. The DAC, ic441 could be having an issue.

[ajvpb]

Re: Denon 3313CI Distorted Audio FL+FR

I have considered poor connections and resoldered all of the pins where connectors are used to join boards together. Doesn't mean its not elsewhere though.

For analog, I used the "CD" input RCA connectors.

I just tested it a few more times and am now getting consistent results - When I power on the receiver and the main amp powers up/relay closes I get static through both speakers for ~15 seconds, then it abruptly stops. Additionally, in that short time I can feel the heatsink on the transistors getting warm to the touch. Far too quickly for a few 15 second test runs. Maybe that is a clue there?

[Ruptor]

Re: Denon 3313CI Distorted Audio FL+FR

I just tested it a few more times and am now getting consistent results - When I power on the receiver and the main amp powers up/relay closes I get static through both speakers for ~15 seconds, then it abruptly stops. Additionally, in that short time I can feel the heatsink on the transistors getting warm to the touch. Far too quickly for a few 15 second test runs. Maybe that is a clue there?

Noise on the amp input will be amplified like any signal and probably make the outputs work hard hence heat. The amp must be working if the analogue signal gives good output. You need to find where the amp is switched between digital and analogue sources and follow the digital path backwards. When things warm up dodgy solder joints can connect and start working.

[Devil_rider]

Re: Denon 3313CI Distorted Audio FL+FR

Does it do it on all the digital inputs? If yes you need to follow path ic406-ic408-ic441. If it is only digital video inputs look mostly at ic101/111/121 depending which input is . Short to ground dafl and dafr signals with 1-10uF capacitor before audio switch to separate the 15 second issue that you noticed. An oscillation in the preamps or dac would overheat the transistors.

[alfatv]

Re: Denon 3313CI Distorted Audio FL+FR

If you have a scope, you check how distorted signal looks and follow through the signal chain.

[ajvpb]

Re: Denon 3313CI Distorted Audio FL+FR

Thanks for everyone's help and suggestions. I've been busy so not able to spend the time I'd like. I played a 1 khz audio test tone and used the oscilloscope to check the connector where the signal leaves the main digital audio/hdmi board. Putting it in multi channel direct, I get no signal on FL and FR and a nice sine wave on the center channel. Which pretty much confirms what we already knew - the problem lies in the digital audio block. It at least eliminates the possibility of a faulty connection further down the line.

Unfortunately some of the IC pins needing testing are on the bottom of the board. I ran out of time to run test leads from the pins in question and power it up, but that will have to wait for another day. I wish the service manual had more detailed schematics of the digital audio path so I could at least go about testing individual resistors and capacitors to see if anything stands out. Oh well, the search will continue another day. Thanks again and I'll report back when I stump myself!