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Mitsubishi M VR700 no audio output

Discussion in 'Troubleshooting and Repair' started by diode, Feb 2, 2016.

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  1. diode

    diode

    12
    0
    Jan 25, 2016
    I picked up one of these receivers from goodwill and it only has audio when its set to max. It is very faint. Does anyone know where I can start testing to see what might be wrong? I would like to use this receiver.
     
  2. shrtrnd

    shrtrnd

    3,781
    497
    Jan 15, 2010
    First thing I'd check is the power output transistors.
     
  3. diode

    diode

    12
    0
    Jan 25, 2016
    how can i check them? i hear a couple clicks when i turn the unit on. do i have to remove them to test?
     
  4. 73's de Edd

    73's de Edd

    2,986
    1,260
    Aug 21, 2015
    .



    Sir diode . . . . . . . please identify yourself . . .1N4148 or 1N4007

    Well you handled a simple amp repair before . . . . try this one on . . . . for MORE of a challenge . . . .


    Quite hard to get audio svc info on Bit-su-mishi . . . fortunately, I think that ONKYO was being the REAL sugar daddy on this units build.

    Check your unit and confirm the LARGE RED star power transformer presence.
    Then the two large massive BLUE star heat sinks and the YELLOW box marked up power transistors will be mounted to the heat sinks at the bottoms .
    Probably, you will be seeing a conglomeration of 2SC5198 - 2SC4468 - 2SA1941 - 2SA1695 . . . . .mixes.

    Do all of your knobs indicators, bells and whistles and displays work all right with the sole exception of the
    weak audio from the speakers ?

    Plug in a set of headphones and evaluate the volume level and degree of control.



    MITSUBISHI LAYOUT :
    [​IMG]
    ( http://i.imgur.com/IzH7CFW.png )


    73's de Edd

    .
     
  5. diode

    diode

    12
    0
    Jan 25, 2016
    Haha I am more of a blown diode these days, hence more free time to repair electronics. That looks like the unit. All of the q numbers match along with the layout.

    Yes all of the functions seem to work but there is no sound from the speakers. When I plug in headphones I start to get sound at about 50 on the dial until max which is 80 or so.

    What Onkyo unit resembles the Mitsu the most?
     
  6. 73's de Edd

    73's de Edd

    2,986
    1,260
    Aug 21, 2015
    .

    Sir diode . . . . . . .

    Oh . . .tayyyyyy . . . . now, with your getting decent and adjustable headphone volume, looks like your failure is not going do be attributed to any involved and serious transistor meltdown.
    Seems like your headphone audio is acquired directly from the main right and left power amp outputs , but power limted by having been fed in through a series pair of 390 ohm resistors.

    Lets concentrate on initially just analyzing the main right and left power amp circuitry.
    Consulting the accompanying schema snippet at the bottom will reveal an overall simplification of this complex puppy by a full 97 %.

    Schema color coding has RED being assigned to the LEFT channel and GREEN to the RIGHT channel .
    Power Output transistors Q523 and Q525 emitters supply your power audio output for the LEFT channel, while Power Output transistors Q524 and Q526 emitters supply your power audio output for the RIGHT channel, their final output is just pass the sets of ultrasonic filters at L501 and L502.
    Physically locate those two units on the chassis, and there should also be 3 additional ones for the RIGHT and LEFT surround pair of speakers and the CENTER channel.
    They are usually air wound with magnet wire and appear as physical variants of :
    ( Relevant photo at bottom of schema page )
    ( But it is being mounted off 90 degrees on its side and usually with less turns than this unit has shown. )
    The nearby RED RED BLACK . . . 22 ohm . . . resistor set should flag them.
    Now you need a test speaker ending in bare wire leads.
    Locate one of the SEVERAL BLACK star ground buss that I have marked in.
    A very convenient one should be at the other HF filter R/C combo of the series 8.2 ohm resistor and 0.1 ufd capacitor, of which, its far end is going to that same common ground buss.
    Power up the unit and have audio coming through your headphones, and thenm unplug them and have the volume up about 25%.
    One speaker lead goes to any one of the the 6 possible same connections being made at the L502 inductor or shunting 22 ohm resistors.
    Then . . . .AND THEN . . .you FIRMLY brace yourself for frontal acoustical impact, as your other loose speaker wire is connected to ground.
    If you are met with success and after wiping that accompanying big smile from your face , move on to test the other channel at its L501, in the same manner.
    If audio is present on both positions , use the mark-ups to further locate The BLUE references to RELAY 501 coil and its two sets of relay contacts, along with the relay driver transistor Q591.
    Pass on to us, the DC voltage being read between its base and emitter.

    Testee-testee time . . . . .

    SCHEMATIC SNIPPET MARKUP:

    [​IMG]


    ( http://i.imgur.com/w6KcBtc.png )

    73's de Edd

    .
     
    Last edited: Jan 25, 2017
  7. diode

    diode

    12
    0
    Jan 25, 2016
    OK I tried testing that with the speaker and I didn't get any sound, I tried on both coils. I am not sure if I checked the ground in the correct spot but I tried in a few spots where that resistor is. I hear a click on the board when I remove the headphones but thats it.
     
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