After Connecting Cable, Analog Inputs Died on Receiver

Discussion in 'Home Theater & Video' started by dastinger, Jul 5, 2018.

  1. dastinger

    dastinger New Member

    Messages:
    17
    Hey guys,

    I own a Denon AVR-3803 surround receiver for 15 years and it has served me well.

    Two days ago, as many times before, I turned it on and, when plugging a RCA -> 3.5mm Jack cable to my computer to listen to some music, there was a loud crackle and the receiver fried. I'm pretty sure I even saw a tiny sparkle between my Macbook (aluminum chassis) and the 3.5mm jack.

    The right channel works but the volume is really low and the left channel only reproduces pops and crackles.

    Speakers and headphones -> same result;
    Digital (toslink) inputs work perfectly fine;
    All analog inputs are toast.

    I know this is a pretty old receiver, but it was more than enough for my needs and I use(d) it regularly. Given its age, I know its value isn't much hence why I'd prefer trying to fix it myself instead of spending its value on a fix.

    Maybe it's only a fuse or something and it would be easy and inexpensive to solve, but I have no clue about where to start. Could anyone provide some guidance? Given the symptoms/cause, what do you think happened? What should I look for?

    Thanks a lot!
     

     

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  2. awillia6

    awillia6 Super Member

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    You say digital inputs work but analogs don't? That doesn't make sense as digitals are first converted to analog before amplification.

    Does the receiver power up normally or does it go into protection mode? Have you reset the unit's microprocessor?
     
  3. imral3

    imral3 Super Member

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    1,634
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    First things first... no more cable plugging while the unit is powered on, right? ;)
     
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  4. awillia6

    awillia6 Super Member

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    1,173
    Possibly a reasonable precaution for vintage and, um, "exotic" audiophile gear. Never had a problem with live connections to mass market consumer rigs including any and all Denon receivers I've worked on over the last 20 years.
     
  5. dastinger

    dastinger New Member

    Messages:
    17
    No protect mode, it powers on normally. I reseted the micro processor and nothing has changed. I made a quick video to show you exactly what's happening. Video was done after I reseted the microprocessor.



    And, yes, I feel ashamed about that one. I usually don't do that ever. Oh well...

    Any ideas?
     
  6. imral3

    imral3 Super Member

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    Have you connected a pair of headphones directly to the macbook to see if the headphone out is what was actually damaged?
     

     

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  7. imral3

    imral3 Super Member

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    Or the 3.5 to stereo RCA cord itself?
     
  8. dastinger

    dastinger New Member

    Messages:
    17
    Nothing but the receiver is damaged. I state at the end of the video that the cord is fine because I've been using it with my old Marantz receiver and the headphone output on the Macbook is fine as well. I tested with the Macbook because of the possibility of showing it working with an optical and analog input with the same source, but the same happens when I connect, for instance, my phone.
     
  9. Markoneswift

    Markoneswift Quartz locked n ready to rock

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    Have you tried any 'direct' or 'straight' modes your receiver might have ? Maybe the DSP got toasted. I had a Kenwood unit that ran fine in line straight mode but went nuts in any of the surround modes.
     
  10. imral3

    imral3 Super Member

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    1,634
    Location:
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    Try another analog input on the receiver.
     
  11. dastinger

    dastinger New Member

    Messages:
    17
    I always listen to music on Pure Direct mode. I know it was on Stereo mode when I recorded the video, but that's because I had just reseted the micro processor. Anyway, that doesn't make any difference. Audio processing on or off, result is still what you hear in the video, unfortunately.

    As stated in the video, I connected it to V. Aux. because it was a random choice. Any other analog input has the same issue. I immediately tried listening to a record after this happened and the same thing was happening on the phono input. And I didn't even have the cable connected to V. Aux when it happened, so it's not a matter of a single input being fried. All of them are.
     

     

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  12. awillia6

    awillia6 Super Member

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    Thanks for the video. Try sending analog audio into EXT IN inputs (FL and FR will be fine so you don't have to change your speaker wiring). Also run the tuner (radio) and see what you get. If it's OK, apply some DSP to the signal (e.g. 5/7 ch stereo) and report back. Also, run a digital signal in (like you did with MacBook) and apply DSP.
     
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  13. dastinger

    dastinger New Member

    Messages:
    17
    Thanks a lot for all your help so far!

    I tried all these:

    • Sending audio through Ext. In works perfectly! With and without DSP.
    • The tuner doesn't work properly. The same symptoms show up. With or without DSP.
    • Digital signal works fine with DSP.
    Did this help or made it more confusing? I really thought we were getting somewhere until the tuner didn't work.
     
  14. awillia6

    awillia6 Super Member

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    1,173
    Sorry, I was out for a bit. Give me a little while to fire up a spare 3803, and I'll get back to you on your problem(s). Not to worry, we'll get the elusive quarry treed sooner or later.
     
  15. awillia6

    awillia6 Super Member

    Messages:
    1,173

    OK, looks like I'll have to change my live connection switching practices. Kudos to "imral3" for calling this one!

    You've blown one (or both) input selector chips, TC9274N-011. These chips select between all the analog audio inputs available and send the selected signal on for A/D conversion so DSP can then be applied. Digital signals are sent directly to DSP since they don't require A/D conversion. After DSP, the digitized, processed signal is then converted back to analog (DAC) and then sent on to the power amp section and out to your speakers (or headphones). The chip is a large 42-pin DIP which is pretty easy to remove and replace with just a soldering iron and a cheap desoldering suction device. Disassembly to get the audio input board out is also very straightforward and, if the unit is disconnected from line power, safe to perform (except for sharp metal edges - watch your fingers!). The chips are readily available on eBay, so if you don't feel like doing the repair yourself, you could always do the disassembly and give the tech both the board and the replacement chip. He should be able to swap it out while-u-wait at minimal cost. Disassembly/reassembly and diagnostic time is what costs with techs. Since you'll have taken care of that yourself, should be a cheap fix.

    Suggest you obtain the service manual for your 3803 so you can see for yourself how the thing is stuck together. The block diagram on manual page 13 shows the different paths for analog (through the switch) and digital signals (bypassing it). The schematic on manual page 84 shows the audio input board circuitry with both selector chips.

    Let me know if I can be of further assistance. Good luck.
     
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  16. dastinger

    dastinger New Member

    Messages:
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    Wow, I wasn't expecting this. It makes total sense and I'll definitely be extra careful with live connections from now on.

    I have a friend who's really comfortable with soldering, so I'll disassemble everything, buy the chips and ask him the favour of doing it.

    Could you, please, confirm that the TC9274CNG-011 would work? That's all I can find on eBay. Even though one listing says TC9274N-011, the pictures show the TC9274CNG-011. If it works fine anyway, I'll go ahead and buy two.

    Thank you so much! Do you have a PayPal account so I can buy you a beer?
     

     

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  17. awillia6

    awillia6 Super Member

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    Yeah, same chip. Suggest you take a close look at the schematic and see if there's a way to determine whether the 2nd chip is good or bad before you waste time and money buying a replacement you may not need. As I recall the 2nd chip is to wrap the selected analog input back to the VCR (tape) OUT.

    P.S. If you really get hung up, I can always swap parts from one of my 3803 to get you up and running while repair of the bad component is pending.
     
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  18. StimpyWan

    StimpyWan AK Subscriber Subscriber

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    I just passed an IPC solder certification course. This included soldering surface mount components and chip sets. So, if your friend is uncomfortable doing the work, send it to me. I could do the work for you. No charge. Just for kicks and grins.
     
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  19. dastinger

    dastinger New Member

    Messages:
    17
    I'd need to verify it asap because all chips I can find on eBay come from either China or Hong Kong so I'm looking at, at least, 20 days, before I get them. So I think i'd prefer to buy two anyway and, if I end up not needing it, I'll send it to you in case you're interested (no charge obviously). I'm looking at a $15 + shipping expense for both of them. It's way less than what I was expecting to spend, so no biggie.

    Thank you a lot for the offer, but I have the Marantz that will do the trick in the meantime. I'm finishing renovations on the room the system is usually in, so all it's doing right now is working as a stereo receiver for music. Good enough for the time being. Again, if you have PayPal let me know, I really want to buy you a beer.

    I'll definitely take up on your offer if he doesn't want to do it. Thank you!!
     
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  20. imral3

    imral3 Super Member

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    Me thinks @StimpyWan is only trying to get a free beer!!:rflmao:
     
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