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Thread: Jvc rx-9v reciever

  1. #1
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    Jvc rx-9v reciever

    Hi again: The receiver was working fine and sounded better in A-B comparisons that just about any I've heard. It sat in my living room for about a year then when I tried it the left channel was low in volume and distorted. I've just begun to work an this and I have the service manual but it is hard to decipher and I don't know how to upload it. With a little help I hope this to be an easy fix.

  2. #2
    Senior Member Enzo's Avatar
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    On most receivers, check the switches, and clean their contacts. Many switches can get electrically dirty, the source selector switch, the tone switches and tone defeat switches, the speaker select switches. A lot of receivers have preamp out and power amp in jacks in back. Some require a jumper plug across them, others defeat those jacks with a switch. Put that on your list. Any tape monitor or recording monitor switches could also be involved.

    If flicking any switch up and down or back and forth makes the left one come back up, even for a moment, that points at the switch being dirty.

    VOlume controls are often dual units, and the balance control could also be involved, so rotate those around to see if they seem dirty.

    Of course it could be a real electrical problem, but my experience is that these dirty contact situations are quite common.
    Education is what you're left with after you have forgotten what you have learned.

  3. #3
    Old Timer olddawg's Avatar
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    I was an authorized JVC tech for over 20 years. What Enzo said. Also check all inputs individually first . This unit is from 1986. It may have a dirty tape monitor switch. It's a very common problem on old receivers if that function is never used. However... the info on this unit says it's "Computer Controled" which meant something entirely different in 1986. If a u is doing all of the switching things won't be so simple. Try testing the preamp out or tape monitor out to see if both channels are clean. If they aren't the problem is in the preamp. Then plug a signal source into the preamp in or tape monitor input. If there is still a channel out I would suspect a power amp problem. A little freeze spray might be your friend. It isn't unusual for signal path capacitors to fail in units of this age. It's helpful to have a scope or a signal tracer.

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    I still need a little help with this and think I have tracked down the problem to some of the low voltages missing on the amp? board. There's lots of boards in this unit.

    It appears all the switching and even the balance and volume controls are done via IC's, there are no pots to be found.

    I've attempted to upload a .PDF service manual without any luck. Can someone explain how to do this?

  5. #5
    Supporting Member The Dude's Avatar
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    1) Click reply.
    2) Click advanced.
    3) Click the little paper clip picture.
    4) Click add files.
    5) Click choose file and select your file.
    6) Click upload.
    7) Click insert inline.
    8) Click done.

    Edit: Ignore the attachment. I was attaching a file as I wrote this just to make sure I had it right.
    Attached Files Attached Files
    “Yeah, well, you know, that’s just, like, your opinion, man.”

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    Dude: I tried uploading but the file never seems to appear in the uploaded file list. Is there a size restriction, would zipping it help?

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    Supporting Member Jazz P Bass's Avatar
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    What size is the file?

    To upload files I simply click on the third icon from the right: "Insert Image".

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    The file is 30.6 Mb. Tried zipping it and still same size. It's a .PDF

    Tried the "insert image" and after spooling awhile it fails to load, post, or enter into the upload library.

    I even tried to find the same file, or any service manual for this unit online, but no luck.

  9. #9
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    The file is 30.6 Mb
    I tried the insert image with no luck
    Looked online too and still no luck

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    img_0405b.jpg
    img_0406b.jpg
    img_0407b.jpg
    I took pictures of the relevant part of the service manual. 1st and 3rd are the same but different shots. Hopefully you guys will be able to make them out. Where I have a problem is in the 1st/3rd drawing, lower left corner, board ENG004 at the connecter.
    The +/- 64 volts is there but none of the others.

    I have carefully checked the other voltages on various connecters and they all seem to be present.

    The problem is 2/3 of the display is not lit and left channel is distorted.

    LMK if I can supply any additional details to sort this all out.

    Thank you!

  11. #11
    Supporting Member Jazz P Bass's Avatar
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    If the file is not locked, you can use "Cute PDF Writer" to 'print' (it sets up as a printer) separate pages or groups of pages, to a pdf file.

    CutePDF :: Product :: CutePDF Writer

  12. #12
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    The file is locked but I was able to use PDF Element leaving a watermark
    AMP SCHEMATIC.pdf
    My question is in the lower right corner on board ENG-004 there is a 12 pin connecter with pins 1-5 labeled 0.0 volts
    Pin 6 is labeled -2.35. this voltage is missing
    Pin 7 is labeled 2.37. this voltage is missing
    Pin 8 is labeled -64.4 this voltage is present
    Pin 9 is labeled 64.3. this voltage is present
    Pin 10 labeled 2.37. this voltage is missing
    Pin 11 labeled -2.35 I think. this voltage is missing
    Pin 12 labeled 0 volts

    So where are these missing voltages coming from and how do I get them back?

    BTW the heavy black line supposedly shows the signal path.
    There are more pages I can provide if needed but this is the schematic

  13. #13
    Supporting Member Jazz P Bass's Avatar
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    The missing voltages are 'derived' from the transistors (Q707/ 709) & (Q712/ 710) being good & properly biased.
    It will take a good bit of detective work to find why the voltages are missing.
    Fortunately the expected transistor voltages are well marked.

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    base emitter collector
    Q707 64.3 64.2 54.1
    Q709 60.9 53.8 0
    Q710 60.9 53.3 0
    Q712 -63.2 -64 0

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    Supporting Member Jazz P Bass's Avatar
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    Q712 is not working.

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    I have the "daughter board" unsoldered so I could work on it. Soldered necessary voltage wires +/- 64 volts, & ground out to it.
    Now when I check the +/- 2.35 volt terminals (pins 11,10 & 6,7) they are all +63 volts. Not even having the right polarity. 11 & 6 should be -

    Here's a pic of the daughter boardimg_0418b.jpg

    Yes the board shows heat discoloring but I have yet to find any bad components.

  17. #17
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    Pretty much stuck not knowing what to check next. Can anyone explain why the +/- 2.35 voltages are 63 volts?

  18. #18
    Supporting Member Jazz P Bass's Avatar
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    That board that you disconnected is the "driver" board for the output section .
    You cannot disconnect it & expect the voltages to be proper.

  19. #19
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    OK, but if I put it back in its inaccessible. When it was in I could only get to the 12 terminals and though the +/- 64 volts were present, the +/- 2.35 were not.
    What about if I have all 12 terminals connected with wire? Say 12" or so?

    I have put the "driver board" back in and now 1/2 of the 2.35 volts are there. But pins 7&6 are +0.9 volts.
    Last edited by bigdrums925; 11-06-2017 at 05:48 AM.

  20. #20
    Supporting Member Jazz P Bass's Avatar
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    Then concentrate on that.

    There should not be any positive voltage on that circuit.
    It is the negative driver.

    Go with the schematic & find where the + voltage appears.

    All of this assumes that you know how to test an in circuit transistor.

  21. #21
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    Looking closely at the 12 pins on the schematic there are voltages listed for some of them. I assume you saw them?

    PINS:

    12 - 0
    11 - -2.35
    10 - +2.37
    9 - +64.3
    8 - -64.4
    7 - +2.37
    6 - -2.35
    5 - 0
    4 - 0
    3 - 0
    2 - 0
    1 - 0

    So I don't know what you mean there should be not be any positive voltage on that circuit.?

  22. #22
    Supporting Member Jazz P Bass's Avatar
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    Thought it was obvious that I meant Pin #6.

    Relist the voltages that you do have now.

    Q707 & 709

    Q708 & 710

    That is where the 2.3 + and - voltages are derived.

  23. #23
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    I took me awhile to remove the driver board again this time feeding all 12 terminals back to the amp board in order to measure the voltages requested
    Q707 Q709 Q708 Q710
    base 63.9 61.4 64.1 61.1
    collector 53.6 0 53.6 0
    emitter 64.0 53.8 63.9 53.5


    Having trouble making the chart readable, it is when I type it but once posted it jams all together

  24. #24
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    I got the voltages back to normal by resoldering the driver board, but seems every time I turn it on they change
    Even the +/- 64 sometimes are at 46?

  25. #25
    g1
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    What ground are you connecting your meter probe to?
    Any chance you have a bad ground connection somewhere?
    Certified Dotard

  26. #26
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    Well after much frustration I was able to get the proper voltages and it works! another dead unit brought back to life with the fantastic help here.
    Thank you all once again!

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