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Thread: Can't find transistor

  1. #21
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    Damn it !
    Now I can't remember how to post a photo.

    Ok here's that connector.
    Last edited by loopyloo; 09-06-18 at 11:56 PM.



  • #22
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    So kay. I got it now.
    They do just lift

  • #23
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    Very interesting ! Not sure I'll need those transistors at all.
    Multimeter testing shows all of the 10 2SC3623a's on the surround board are good. Haven't checked the 2 on the main board.
    When it was looked at way back in time, it had channel problems but I couldn't remember exactly what it was, I thought I remembered 2 or 3 of them not working. Well it's only the center speaker giving trouble. The other channels work fine.
    This unit is capable of giving out a test tone of white noise for checking and adjusting volumes etc. The test button is on the remote. The test sound is sent to the speakers in a circulating pattern.
    What I found goes like this :
    The unit can play to 5 speakers (channels), L+R front, L+R rear and Center.
    There are 4 speaker modes, Phantom, 3Ch logic, Normal and Wide. The center channel relay is on with 3Ch logic, Normal and Wide but not Phantom so I'll leave Phantom out out of this discussion.

    Left and Right refer to front speakers.
    "3Ch logic" pattern is : Left, Center, Right. While Center is engaged, the sound comes from both front speakers at lower volume.
    "Normal" pattern is : Left, Center, Right, Rear. While Center is engaged, the sound comes from both front speakers at lower volume.
    "Wide" pattern is : Left, Center, Right, Rear. While Center is engaged, there is no sound at all.

    So what do you think ?
    Faulty IC300 maybe ?
    Last edited by loopyloo; 10-06-18 at 07:30 PM.

  • #24
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    Quote Originally Posted by loopyloo View Post
    Very interesting ! Not sure I'll need those transistors at all.
    Multimeter testing shows all of the 10 2SC3623a's on the surround board are good. Haven't checked the 2 on the main board.

    So what do you think ?
    Faulty IC300 maybe ?
    That is not the way how you test these things !

    What voltages and signals do you have on Q307 when the center is activated?

    You need to point your CRO to the emitter of Q307 to see if there is an audio signal. If not look at pin 34 of IC301.

    I do not see IC300 processing the center signal.
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  • #25
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    Q307 has voltages that match the schematic. E 0, C 0, B -12.
    And yes Q307 emitter has a signal at the right time.

    Something else I thought was a little strange.
    It's been in the "Wide" mode during tests, so every time the unit is turned on it will be "Wide" unless I change it.
    Wide mode tone test circulates : Left, Center, Right, Rear. It stays on each for about 2 seconds.
    When it was first turned on, the right didn't work. So it was Left working, no Center, no Right, Rear working.
    I turned it off and on again to restart it and got no Left, no Center, Right working, Rear working.
    I tried restarting it about 8 times and got different setups. During this, the Center never worked.
    Weird ! It's doing some sort of random switching that it shouldn't.
    When I looked at it the other day, I turned it on and off many times while fiddling with the speaker wires and other things and only played music. During that time the center never worked but the other channels never failed.
    There must be a clue in there somewhere.
    Last edited by loopyloo; 12-06-18 at 01:11 AM.

  • #26
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    I traced an audio signal at pin9 into the volume board and pin3 out.
    Signal is also at IC601 pin 1 (input) but no signal at pin2 (output).
    STK350-130 is around $14 + post.

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