RX-900/U service manual

Discussion in 'Yamaha' started by rcs16, Aug 5, 2018.

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  1. rcs16

    rcs16 Super Member

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    Baldwin, Ontario, Canada
    Hello,

    I have a RX-900/U with some problems with the tuner. The service manuals I found online have the tuner pcb component layout info missing. I am wondering if anyone has this missing information to share . I believe it is pages 25,26.
    One of the power amp channels were blown to bits. I managed to rebuild the amp channel and get it going again. I have the parts list of replacement components which I can share if anyone is interested.

    Thanks
    Rick
     

     

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  2. rcs16

    rcs16 Super Member

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    Disregard the search for the tuner section comp layout, it's up and running again. the layout is fairly easy to follow.
    Funny as to what havoc a o/p bjt case to ground short will cause. Most would throw it in the junk pile and not invest the hours to track down the faults. To hot outside today, hide in the basement and play with my toys, wife is out of town too :)
    If you are interested, refer the schematic, it was Q502,511,515,530, IC503(NJM4558S) I am lucky I did not fry more or it would be all parts, esp if the controllers were fried.
    The detector opamp, ic503 had its o/p pin 8 at 0VDC, it should be the same as the NVCC reference(~4VDC) at the -ve i/p. I swapped in the same part from the ic519 position, power up, check the bias, correct and the magic music happened. Couple of ksa945cy and ksa733cy and a 4558S opamp. I can now roll in a new opamp since I used a socket.
    It is not a T-85 tuner but I'd say it is better than most receivers except for some high end ones. It is sensitive and the narrow IF bandwidth helps with rejecting adjacent carrier splatter. A cheap 3 gang tuner module using a jfet and bjt mixer.
    The amp design is quite good, it uses a cascoded VAS except they cost reduced and used one set of low power (100W) o/p bjts, Toshiba 2sc1382/2sa1265. Swapping in NJW3281/NJW1302 (200W) will help with 4 ohm loads. two pairs of NJW3281/NJW1302 (200W) would even be better but the transformer and filter caps are pretty small for power.
    All in all, not too hard to service this model. Few mechanical switches in the signal path.

    the dogs are barking as my fav radio station is playing Pink Floyd Animals as a reward to me. Another great tune, Tom Cochrane's Lunatic fringe, we have great tunes here. have a nice weekend long one for us canucks.
    Cheers
    Rick
     
    Last edited: Aug 6, 2018
  3. avionic

    avionic " Black Knights " Subscriber

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  4. rcs16

    rcs16 Super Member

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    Location:
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    Thanks but it is the same pdf as the hifiengine copy. Not sure if I want to invest in a proper manual, good for now.
    Even the RX-1100 is very similar and that manual copy has the same issue with no tuner pcb layout drawing. those fold out pages tend to get forgotten.
     

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