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DENON AVR3300 no FM reception

Discussion in 'Electronic Repair' started by Brasto, Sep 10, 2007.

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  1. Brasto

    Brasto Guest

    I like to restore the FM reception to normal ops. So far I have
    diagnosed that AM reception/tuning is in good condition. In the FM
    mode no IF signal is getting to pin 1 of the IC LA1265 so I belief
    that the little tuner block is at fault. I managed to remove the
    shielding covers to get access to the tuner section which really
    exposed a jungle of SMT devices.
    To find my way around this multigang-ed tuner I hope that some one can
    provide me with a copy of the DENON FM front end or any help to
    troubleshoot the receiver

    Thanks
    Bram
     
  2. JANA

    JANA Guest

    Firstly, verify that there are proper supply voltages getting to the tuner
    unit. If the receiver is digital controlled, check to see if the tuner unit
    is being properly commanded by the uPC. Check to see that the local
    oscillator and RF amp in the tuner is working.

    If you replace any parts in the FM front end or do any kind of soldering,
    you will need the instruments and skills to perform the front end
    calibration if you want peak performance from your receiver.

    You will need a good scope and the full service information to properly
    troubleshoot the front end of your receiver. If you call the parts
    department for Denon, I believe they will sell you ca copy of the service
    manual and any parts you need.

    --

    JANA
    _____


    I like to restore the FM reception to normal ops. So far I have
    diagnosed that AM reception/tuning is in good condition. In the FM
    mode no IF signal is getting to pin 1 of the IC LA1265 so I belief
    that the little tuner block is at fault. I managed to remove the
    shielding covers to get access to the tuner section which really
    exposed a jungle of SMT devices.
    To find my way around this multigang-ed tuner I hope that some one can
    provide me with a copy of the DENON FM front end or any help to
    troubleshoot the receiver

    Thanks
    Bram
     
  3. I have sent a diagram of the tuner section to your gmail address. A quick
    glance suggests that pin 5 is the voltage contolled tuning input;
    transistors TR 505 and 504 appears to be the AM and FM switches.

    Mark Z.
     
  4. Brasto

    Brasto Guest

    Mark,
    That is great info and probably will lead me to the desired
    result......
    In the mean time I took another DENON unit apart which is a working
    straight forward AM/FM tuner. It's front end is from a different
    manufacturer and has a different format/technology, but it also had 8
    pins with the same pitch as in the AVR3300. I decided to swapp both
    tuners and guess what....the suspect works as advertised and the known
    to be good tuner did not function in the AVR3300. So I learned at
    least one thing...my front end is OK. I also learned that the AVR3300
    does NOT provide the B+ and the Tuning Voltage is stuck at B+ value. I
    am still struggling to understand all the *# Note numbers in your
    schematic telling that things are OPEN. Is your schematic covering
    various versions of the AVR3300 ?.
    E.g. top LH corner shows Front End with floating AGC line and
    additional pins 9, 10 and 11 which do not exist in my unit and a bunch
    of akward connected resiustors.R504...R571)
    Am I correct assuming that IC 507 (LC72131 is generating the VCO
    voltage to pin 5 of the front end ? and also switches via pin 10 the B
    + thru TR505 ? I am afraid I might end up with a Buss problem in the
    PLL circuit ?

    Thanks also to JANA who pointed out that the drive signals from the
    Uprocessor might be wrong rather than the tuner itself.....
     
  5. I don't know what the story is on those extra pins - Denon's service manuals
    can be pretty crappy, especially these scans of their older ones.
    I think the PLL IC is probably bad - this is a pretty common failure.

    You can apply an external tuning voltage to the front endm vary it through
    the range and see if the tuner tunes, and also that there is an oscillator
    output, but of course there should be, since you've pretty well found the
    front end to be OK...
    I think so; also bear in mind that the AM/FM switch outputs on pins 10 and
    12 of IC 507 would each be high and low at any given time - that is, they
    should not both be at the same state at the same time. This is another type
    of failure the PLL IC could have.

    Mark Z.
     
  6. Brasto

    Brasto Guest

    ...Oeps..Got myself in deeper trouble..I had this suspect front-end
    swapped into a known to be good tuner TU580RD, it performed OK that
    day. A few days later I reapplied mains to the TU580RD and NO more FM
    reception. I then reinstalled its original front end and gray
    hairs...it did NOT work any longer. Measurements showed that B+ had
    gone. Doing some PCB line tracing ended up to SMD TR23 failed to
    switch +12 VDC when so commanded. Removed the bug from the board and
    patchwired +12 VDC to B+, Life returned to the TU580RD. I now have a
    need to know Type/PN of the SMD switch (No markings left) at PCB
    location TR23. ?? Who can help ??

    So I learned the hardway that my original frontend from the AVR3300
    probably developped a short in the B+ over times. I put the suspect
    frontend back into the AVR3300, disconnected its B+ PCB jumper wire
    and applied an external 12 VDC. No smoke but a full short..Let me tell
    you that probing around in the tiny little front end is a challenge of
    its own. Some engineer must have thought that RF leakage shall be
    minimized by soldering a tripple housing at all the fingerstocks.
    Unfortunately the circuitdiagram Mark so kindly provided to me does
    NOT cover the front end. DENON has classified this part probably as a
    Black Box....Sealed Do Not Open....

    I'll just wait for another FM unit to canibalize its front-end
     
  7. Brasto

    Brasto Guest

    Well, it's an A OK, ordered a new Front end (Mitsubishi) and replaced
    the SMD T105 (RN1205) which failed to switch the 12 V B+ to the front-
    end.
    The old front-end had obviously developed an internal short on the B+
    line with temperature/time. I still donot understand this because
    according to some lay-outs there is always 100 ohms in the internal B+
    circuit. Probably that a short develops underneath one of the SMD
    components and a tiny PCB trace.

    Anyway, again thanks for your help(s), It saved another fine product
    from the trashcan...
     
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