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Denon Receiver Acting Strange

Discussion in 'Troubleshooting and Repair' started by Stoopalini, Nov 30, 2011.

  1. Stoopalini

    Stoopalini

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    0
    Nov 30, 2011
    I have a Denon AVR-987 receiver, which has been great for the past 4 years, but has recently started giving me problems.

    At 1st, I would hear a 'click', and the sound would go out. This is with the speakers connected to the internal amps (via binding posts). I would turn the unit off, then back on, and the sound would return.

    Then, the same thing happened, but in addition the HDMI video stopped being passed as well. A reset by powering on/off did not fix it either. I tried the CPU reset (holding buttons while cycling power), and it didn't help. All other functions seem to work (display, input select, etc ...). Even when I selected the 'Tuner' input I still received no sound. Also, interestingly, during this troubleshooting, I noticed the volume knob no longer changed the dB readout on the display.

    So I removed the unit from my entertainment center, and about a week later, looked inside and found nothing obvious. I hooked it up in my office to test it out and it started working fine again.

    So I reinstalled it in my entertainment center, but used external amps with the pre-outs thinking maybe the internal amps were causing too much heat. This worked for about 2 weeks, but now the original problems have resurfaced (Audio 1st, then both audio & video), even with no speakers connected to the binding posts.

    I am decent with a soldering iron, and have the tools, but no idea where to start. I called a repair facility, but they charge $69 just to diagnose and stated it will probably be no less than $200 to repair.

    Is there a way to permanently disable the internal amps? Can I just remove the speaker protect fuses to do this, or will that also disable the pre-out circuitry as well?

    Any common issues with this type of receiver I can check for?

    Thanks for any assistance!
    Thomas.
     
  2. davenn

    davenn Moderator

    13,342
    1,773
    Sep 5, 2009
    ok a service manual with a circuit diagram will probably be essential to answer tose questions.
    Do a search on google for the make and model and see what you come up with. There are several manual repositries online you may be lucky :)

    withoout a cct diag. we would just be guessing

    Dave
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    9,394
    1,918
    Nov 17, 2011
    Well, i don't know that particular receiver, but let me offer a guess anyway: Since cycling the power helps and also using external amps (which reduces internal power consumption), the problem could possibly be blamed on some faulty capacitors in the power supply. Another sign could be audible hum - have you noticed some?
    This will not be obvious through visual inspection. You may
    1) de-solder the power caps in the supply and check their capacity with a capmeter or
    2) solde some comparable capacitors in parallel to the existing caps in the power supply, then check function.

    Regards,
    Harald
     
  4. Stoopalini

    Stoopalini

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    Nov 30, 2011
    Thanks guys. I have the service manual in PDF format, but cannot upload it to this site due to the file size (18MB). Is there a repository you can recommend for me to post it so you can access?

    I haven't noticed any audible hum, either from the speakers (when they were hooked up) or from the unit's electronics. I was thinking a heat related issue due to the elapsed time it takes for the problem to present itself, but it's just a guess on my part :confused:

    Thanks for your help,
    Thomas.
     
  5. davenn

    davenn Moderator

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    Sep 5, 2009
    ok on having the service manual.

    do screen prints of the circuit diag and just post those in gif or jpg
    reduce them in pghysical size to ~ 604 x 480 pixels

    cheers
    Dave
     
    Last edited: Dec 1, 2011
  6. Stoopalini

    Stoopalini

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    Nov 30, 2011
    The service manual has a ton of diagrams, and I'm not sure which ones to post. I will try to upload it to Google Docs and post the link

    Thanks,
    Thomas.
     
    Last edited: Dec 1, 2011
  7. davenn

    davenn Moderator

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    Sep 5, 2009
    Hey Thomas

    that makes it a bit easier to ponder the workings.

    OK its unlikely that a fault in any of the power amps would be stopping all power amps from working and also stopping all the preamp outputs from working.

    One thought is that the muting circuitry is just cutting in randomly for some unknown reason.
    Do you have an oscilloscope ? it would be really useful to trace an audio path whilst the unit is in fault condition and see where the audio stops. Then you would have an idea of what part of the system is at fault.

    Dave
     
  8. Consultant

    Consultant

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    Dec 2, 2011
    Hi Thomas,

    Whenever I was trying to repair things, a good list of "symptoms" like you posted really helps any service engineer. So thank you for that!

    OK, next stage is to rule out as much as possible and hope your supositions are correct...

    To take your points in order then.

    The click is most probably the collapse of the output, a "de-thump" circuit (if present) is not stopping this, so it most likely is a unexpected catastrophic failure, not an orderly attentuation such as current or voltage foldback by the amp or PSU. Basically the machine is most likely not "expecting" this fault.

    After four years, it's well out of "infant mortality", so is likely age-related.

    Cycling power at first cleared it.

    The HDMI video stopped - That could be due to DRM cutting in, if it is suspecting the electronics have been "modified". This could not be cleared by cycling the power.

    The other digital functions seemed to work even during the fault condition - Good, this sounds like it could rule out almost all the digital side and PSU I suspect?

    That means that we have it down to somewhere from the audio demutiplexer (audio switching) to the speaker. Basically the analog stuff.

    It cannot be the input of the demultipler, or switching inputs would create some sort of sound - I take it, it was completely silent, no hiss or hum?

    The volume knob no longer changed the dB readout. Would it "stick" at the last volume it was set to, or at the same dB everytime?

    You did everything right! Using external amps was excelent diagnostics as the original problem returned, clearing the power amps of blame. Now it could just be one speaker going open circuit and causing both power amps to go into self-protect mode. Did you use different speakers with the external power amp, or the same ones?

    The external power amps worked for about two weeks again. A true catastropic failure of a component would mean it would never work, so it is an intermittant fault we are looking for then..

    'Scoping everywhere during fault conditions would help, but my suspicions say dry joint,crack in track somewhere from the output of the audio switching, to the output of the preamp. If you cannot find any, then desolder and check/replace any capacitors around there - Especially electrolytics. You could try checking any resistors around there for any cracks in them, or possibly out-of-tolerance.

    If you cannot find anything, then you need a hot soldering iron, a hair dryer and some electronics freezing spray. Freeze things area by area until the fault disappears. Use the hair dryer if necessary to make it appear again if necessary to narrow down the area where the fault is. If you still cannot get it, freeze it again so it goes away and hold the hot soldering iron near each component in the area you have narrowed it down to, until you can prove which one is intermittant. It just might be the pre-amp semiconductor, but I suspect it will be a discrete component or just as likely PCB-related like an intermittant dry joint has developed.

    Good luck!
     
    Last edited: Dec 2, 2011
  9. davelectronic

    davelectronic

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    Dec 13, 2010
    Thats certainly going to keep you busy, i suspect it will be found fairly easily, davenn's approach seems the way to go, i am no expert on amps recievers etc, but there is some thing in all the posts so far more than worth a look. Good luck in your fault finding, always interesting to see a positive out come, watching on the side lines, good luck with the fix.
     
  10. Stoopalini

    Stoopalini

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    0
    Nov 30, 2011
    I don't have an oscilloscope, but I can probably get my hands on one if needed.

    I don't think it's the muting circuitry, as both video and audio stop being passed. Switching inputs once the problem manifests does not create any sort of noise out of the speakers (running off separate amps from the pre-outs). The volume dB readout would 'stick' on the last value when the input was changed, so a problem in the audio demutiplexer sounds probable.

    Can you tell from the service manual which board this is? If would definitely help me narrow down my search.

    Also, it's interesting to note I've found several others who have this same problem with this receiver. If you read post 3947 in this thread, you'll see what I mean.

    Thanks again, I appreciate the help.
     
  11. davenn

    davenn Moderator

    13,342
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    Sep 5, 2009
    using a scope is really the easiest way to trace the signals.

    you basically just need to start at one of the inputs ( with an input signal connected) and work your way into the system till you loose the signal.

    Of course taking not that you have input selector switches switched appropriately etc

    Dave
     
  12. Consultant

    Consultant

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    0
    Dec 2, 2011
    Thank you very much Stoopalini for your answers.

    One of your clarifications seems very significant to me? The volume control sticking at the last setting and not some pre-set value drags my interest away from the multiplexer and right at the volume control itself.

    Typical problems around there can be incorrect voltage, incorrect clock signal, corrupted or corrupting audio data, corrupted or corrupting the I2C data and lock-up from the remote control sensor going out of tolerance.

    Remembering that cycling the power does not clear it, but leaving the power off for some time will, that is making me suspect a heat problem - Overheating semiconductor, discret component, or dry joint. If there was some error condition occuring and it was the stored charge in the capacitors that what was preventing the error from clearing, then cycling the power would not have cleared it at first. It did, but does not any more, that suggests the fault is worsening over time.

    My next step would be to see if we can rule some more out. When the unit is displaying the fault, can you still change the audio inputs WITH THE REMOTE, not the front panel? If so, is there any sound at all, even a crackle?

    My thinking was that if there is there some problem with the sound, the system may be detecting "tampering" and the digital rights management was blanking the video section? However some other problem, like corrupted data on the I2C bus, or incorrect voltages might be causing the video problems in the electronics, not programing.
     
    Last edited: Dec 5, 2011
  13. Stoopalini

    Stoopalini

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    Nov 30, 2011
    I did a bit more looking into this today, and found some interesting results.

    I reconnected the receiver up, and the problem was present. No sound/video, volume does change dB readout. Changing the input causes the dB readout to lock at the present setting. This is after sitting for several days. I then did a factory reset procedure, and it started working normally again.

    I have it setup with a stereo input signal going into the CD input, and the front L & R pre-outs hooked to a set of powered studio monitors.

    I ran it for a few hours, playing some low level music through the front preouts, with the cover removed, and the thing got very hot. I'm surprised it's getting so hot, especially with no speakers connected to the binding posts and the top cover removed.

    I then connected a speaker to the front channel binding posts and started pulling fuses and powering up to see if I could find one (or two) which would disable the integrated power amps. I didn't find any which did so, but did notice a few strange things about F 13 &14.

    If I pull both 13 and 14 fuses together, the unit exhibits the exact same symptoms as the problem. Power on and no sound, dB readout changes with volume knob. Change inputs, and the dB readout locks. I tried to understand the schematics enough to know what these 2 fuses are doing, but it's over my head.

    Pulling just 13: Everything works fine on initial power up. Audio passes through and the volume knob works as expected. Changing the input to something else, then back to the source causes the audio to drop and not return, but the volume knob continues to change the dB readout. Power off/on, restores the audio.

    Pulling just 14: Everything works normally. Changing inputs works normally, as does the volume knob.

    I then got out my meter and was going to go through the idle current setting in the service manual, but I don't think my cheap meter is up to the task of measuring 6.5mv LOL! at the 200mv setting, the meter fluctuates too much to take accurate readings. I called my brother, who does have an oscilloscope, but he said it's been sitting in his shed for years and hasn't been calibrated in who-knows-how long.

    I then reseated of the cables which interconnect the boards in the unit, and will run it for a few days to see what happens.

    I appreciate the help thus far!
     
  14. Stoopalini

    Stoopalini

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    0
    Nov 30, 2011
    So I left the receiver on over night, set to 7 channel stereo, with a stereo signal feeding it through the Analog CD input. Everything is still working today, with no sign of the issue.

    It's still getting fairly hot, so I'm considering installing a 12v fan inside the case, over the heatsink someplace. I felt above the heatsink, looking for the hottest location, and it's on the left side (in the pic), close to the rear panel.

    I also noticed a small component attached to the heatsink I don't recognize. Any chance this little thing is heat sensitive, and is triggering the unit to go into a protect mode when it heats up too much?

    [​IMG]

    Here's a closer shot:

    [​IMG]

    The markings on it are: "B2", a symbol which looks like an 'M' inside a circle, and the numbers "69". It's soldered onto board 1U-3702-1 "P.SUPPLY UNIT" in the IC608 location.
     

    Attached Files:

  15. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Hi,
    chances are the component labeled "B2" is a thermistor uised for sensing the temperature of the heat sink. In that case it could be used to tirn off the amplifier in case of overheating, as you suspect.
    This wouldn't directly explain why the volume control gets stuck - unless this is a bug in the control software of the receiver (not unlikely).

    But: If the thermistor is the cause of the muted receiver, the it's for a reason. As you noted parts of the receiver become very hot. So I suggest looking for the cause of the power dissipation causing the overheating. Can you locate the heat spot (an overheated transistor, resistor or similar)?

    It is probably not a good idea to tamper with the protection circuitry unless you have ensured that everything else is in good working order.

    Regards,
    Harald
     
  16. Stoopalini

    Stoopalini

    8
    0
    Nov 30, 2011
    Thanks, I figure if it's cutting out due to heat there must be a component failure somewhere. And considering the power amp probably generates the most heat, I was hoping there would be a way to disable them.

    I've looked through the service manual, and tried experimenting with removing various fuses, but can't find a way to do this.

    If someone could take a look through the schematic diagrams and possibly identify a way to disable the amps, I would really appreciate it :)

    Thomas.
     
  17. woodfin

    woodfin

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    Feb 14, 2012
    same issue

    I have the same Denon AVR-987 and it does the exact same thing. Click, then sound cuts out and won't come back, plus the volume control freezes when you switch inputs. Turning off the unit brings back the volume control but not the sound.
     
  18. 7racecar7

    7racecar7

    1
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    Mar 2, 2012
    2807 Same issue

    I have a 2807 with the same problem with the speakers not turning on and the volume control not changing, i had it repaired a year ago through a denon certified place it was about 80.00 but the part was like 1.50.

    I just fixed my TV that had a similar problem with turning on, an issue with the capacitors and not having the correct voltage.

    Anyone think there could be a capacitor issue here? I can unplug the unit for 24hrs and all of a sudden the speakers work for a day. When it doesnt work it clicks with an initial click with the lights coming on only on right side speakers then a delay about 10 sec then a hard sounding click and nothing.

    when it works the initial power click happens then right after about 2 seconds a soft click comes on and then you see all the speaker lights on the left side and the sound works.
     
  19. woodfin

    woodfin

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    0
    Feb 14, 2012
    I just got the receiver back from Denon Service and they said they could find nothing wrong. Haven't hooked it up yet, will let you know what happens. I did find a bad cable on removal but took it in anyways as I already had it all disconnected. I have never had a bad cable take down a whole system but, maybe this unit is more sensitive than others.
     
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