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Denon AVR-3300 - intermittent audio out

Discussion in 'Electronic Repair' started by Ken123, Sep 21, 2007.

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  1. Ken123

    Ken123 Guest

    Hi, Y'all...

    I got a good deal on this off eBay. The seller indicated problems, but they
    seemed to involve only digital sound inputs. I mainly planned to use it for
    analog sound, so I figured that would be no problem.

    It worked great for a few days until sound output to the speakers started
    disappearing when I switched input sources, including tuner.

    While troubleshooting, I discovered if I flexed the top of the Audio/DSP
    card the sound would return, and the receiver would start working
    normally...for a while. The speaker relays can be heard switching when it is
    operating normally, but not when it isn't.

    Then again a little later, no sound after switching sources. Again I flexed
    the card and the sound returned. So, brilliantly, I figured keeping the card
    flexed with a small cable tie would solve my problem! It did - for a few
    days. Then the problem returned.

    I removed the card and inspected it carefully, and could not spot any
    obvious smoking gun. All solder joints, traces, connectors look normal. No
    bulging caps.

    With these meager clues, is there a Denon AVR expert out there who could
    suggest what I should look for? Thanks.

    Ken
     
  2. The problem with bad solder joints and cracked traces is that they are often
    difficult-to-impossible to see.

    We recently had a similar problem that was traced (joke intended) to a
    cracked trace under an IC.

    I would start systematically unsoldering and resoldering every joint on the
    board. It's not enough to melt the solder and push it around. You need to
    suck or wick it off, then apply fresh solder, preferably eutectic (63/37).
     
  3. Arfa Daily

    Arfa Daily Guest

    How does your company make a living dealing with such dry joint problems by
    sucking or wicking every joint before resoldering ? Just interested, as I
    sure wouldn't be able to spare the time to approach it like that, and still
    keep it financially viable. For sure I agree that just reflowing the joints
    is not really enough, but I don't think that I know anyone else in the trade
    who deals with bad joints in any way other than just reflowing with a touch
    of new solder added, whether they are reworking an obvious bad joint, or
    carrying out a 'blanket solder-up' job of an area that has an invisible bad
    joint.

    I do sometimes clean old solder right off, but only when there are obvious
    signs that the chemical composition of the joint has deteriorated beyond
    recovery - for instance where a joint has gone crystalline as a result of
    being subjected to continuous heat-stress from the component that it is
    connecting.

    To the OP. I have had a number of problems with bad connectors on Denon AV
    amps. Just because the connectors 'look' good, I wouldn't immediately
    dismiss them as being blameless. It would be worth squirting some switch
    cleaner in, and then 'working' the connector in and out a few times. Also,
    if you have the facilities / expertise, its worth reworking the joints on
    the surface mount DSP ICs

    Arfa
     
  4. How does your company make a living dealing with such dry-joint
    It doesn't. I'm an individual who's been repairing electronic equipment, on
    and off, for almost 50 years.

    I learned a long time ago that there are two ways to repair something --
    find out exactly what's wrong, or do whatever's needed to get the damn thing
    working again. Neither is the "best" approach -- it depends on the problem.

    In this case, it looks as if there's a bad solder joint -- or perhaps a
    cracked trace. It's less trouble to systematically resolder the joints than
    try to find the "bad" one. Note that two recent posters to this group have
    had good luck doing basically that.

    The problem with just adding a bit of fresh solder is that there's no
    guarantee you're really getting the solder into its "liquidus" state. It's
    better to remove the solder altogether, so you can see what you're doing. If
    you have a SoldaPult, or a similar tool, it's not much trouble to quickly
    remove the solder from a dozen or so joints.
     
  5. Ken123

    Ken123 Guest

    I would start systematically unsoldering and resoldering every joint on
    I appreciate the suggestions. There are about 70 pins connecting the
    Audio/DSP board, but I think I'll go ahead and re-solder each of them.
    However I had to remove about 100 screws to disassemble this thing, and I'll
    have to pretty much reassemble it to test whether the resoldering worked.
    But what the hell, I'm retired!

    Ken
     
  6. Smitty Two

    Smitty Two Guest

    No, but it's enough to add a drop of liquid flux to each joint and
    reflow it. Solder isn't spackle that you spread around. Wicking off all
    the old stuff just to put on new stuff will take about thirty times
    longer than adding some fresh flux, which is what you're *really* doing
    when you put on fresh solder.
     
  7. Arfa Daily

    Arfa Daily Guest

    Agreed.

    As far as the practicalities of removing old solder go, I have a proper
    vacuum rework station which removes solder from a joint almost as quickly as
    just resoldering it, but I still wouldn't, under 'normal' circumstances, use
    it to remove the solder from every joint on a board before resoldering. I
    think that it's probably down to a degree of how much time you have on your
    hands and personal preference, if you are an experienced solderer. I only
    questioned your original post because you said in it "we recently had a
    similar problem ..." I (obviously wrongly, sorry !) assumed that "we"
    referred to a repair shop. I don't have a problem with you using this total
    removal technique if that's what works for you.

    I agree that sometimes a joint which appears to flow when an iron is
    applied, may not have reached a correct liquidus state throughout, but as an
    experienced solderer yourself, I'm sure that you would agree that when this
    happens, it is pretty obvious to the 'knowing eye', and that's the time I
    reach for the vacuum iron.

    I would however, question the technique from a professional point of view,
    for finding *most* bad joints. There are very good techniques for finding
    the rogue ones - a can of freezer spray for instance - and a 'blanket'
    resolder of an area is always a last resort for me, if all other methods
    have failed. Particularly on a densely packed board, a 'blanket job' opens
    the way for creating further problems with unintentional ( and unspotted !)
    whiskers across joints. With the best will in the world, I think we would
    all agree, it happens ...

    Interesting to hear how other people go about jobs, and how the juggling act
    of practicality versus profitability is looked at and resolved by
    individuals.

    Of course, there's lead-free bad joints to contend with now, and as we all
    know, they defy *all* the proper techniques that we know and love ...

    Again, to the OP. As you surmise, you will probably want to screw it back
    together before retesting - particularly any screws which pass through the
    back panel into phono ( RCA ) socket blocks which have a built in grounding
    strap at the screw hole. Some of these AV amps are super-critical of rear
    panel grounding, and can cause you no end of problems with the protect
    circuit cutting in with the slightest disturbance, as ground connections
    come and go ...

    Arfa
     
  8. In my experience this is a matter of resoldering the flat-pack IC's on the
    DSP board. Your average doit-yourself-er is unlikely to have the necessary
    soldering skills or equipment to deal with the fine pitch of the IC leads
    involved.

    Mark Z.
     
  9. jango2

    jango2 Guest

    Hi,
    I just fixed a Denon AVR-1905. I'm probably one of the 2 recent
    posters that William refers to. I'm not familiar with the AVR-3300 but
    i just wanted to point out that the problem might not lie in the DSP
    board. When you flex the pcd you might be subjecting the cpu board to
    stress causing a pin of the cpu to make /break contact, as it is the
    main board and other pcbs dock onto it. I think you should reflow the
    cpu. I finally resolved my case with the use of a scope, service
    manual and magnifying glass. Observe and trace waveforms like data and
    clock all the way to the pins of the cpu. Like William said, my break
    was under the flat pack.
    Jango.
     
  10. Ken123

    Ken123 Guest

    I'll check that out. Thanks.

    Ken
     
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