Technics SU-VX800 Repair Help

Discussion in 'General Electronics Chat' started by BlackSoldier, Feb 17, 2011.

  1. BlackSoldier

    Thread Starter New Member

    Jan 18, 2011
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    Hello all, I am a new member and I have the above mentioned integrated amp that I would like to get some help to repair if possible. It worked great except that it would lose sound until I turn it off and turn it on again. It did that for a while but now I get no sound whatsoever. All the knobs etc. are working because I can select different sources and I can see that it is in fact playing from looking at the EQ attached to my setup. Sometimes I will get a loud static sound but nothing else. whenever I get the sound it will also sometimes go into protection mode.
    It is a great sounding amp(whenever it was playing) and I don't want to get rid of it. Can anyone help me pinpoint the problem? Thanks in advance for all your help.Attached are pictures of the inside. As can be seen in the pix, there is an area that looks burned or something. Could that be the problem??
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    That may or may not be the problem.

    Is the current drive LED active after power up?
    Do u hear static when you crank up the volume without an input?
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    From the manual, the two transistors that look a bit worse for wear are Q652 and Q654.

    hgmjr
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Hmmm.. tht could be the culprit for the static noise.

    They are the Voltage regulators for the servo circuitry. Since this amp is DC coupled, any offset voltage in the pre drive area will be amplified as noise.

    OP's problem could be leaky transistors or the IC651, the so called "servo" amp. which is a low noise high quality opamp.
    It is advisable to replace the regulators with higher wattage transistor pairs or provide a small heat sink to prevent further e PCB charring over time.

    The transistors are same as the ones used in the voltage amp circuitry. A high voltage, a with an Ic of 2Amps. A typical TO-220 plastic type....
     
  6. BlackSoldier

    Thread Starter New Member

    Jan 18, 2011
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    R!f@@, I will hook it up and check for all those things you suggested later tonight when I get home from work. I will keep you posted on what I find out. Thanks again. Thanks again guys for all your help so far, again I will keep you all posted.
     
  7. BlackSoldier

    Thread Starter New Member

    Jan 18, 2011
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    R!f@@, when the unit is powered on the current drive led comes on after a few seconds but when I crank the volume I do not hear any static that I can tell. At one point when it was powered up and I turned the volume knob, I heard a popping sound then it went into protection mode again.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    That manual will give you something to guide troubleshooting. Do you have a meter? That would be a very valuable tool.
     
  9. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Preliminary check says that the amp's Voltage and Current drive LED's light up.
    And u don't hear anything from the speakers when u max the volume.

    Is this correct?

    Here is a test that u can do if the both V & I LED's do light up
    Without an input at max Volume u shud not hear even as much as whispering white noise. Amp should be quite.
    Now rapidly turn the volume up & down, see whether u hear any thing.

    Next keep the volume at a moderate level and switch the input selectors from all the way, left to right and so forth and see whether u hear anything.

    Post back.
     
  10. BlackSoldier

    Thread Starter New Member

    Jan 18, 2011
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    R!f@@ that is correct. I tried both tests that you suggested and I did not hear anything from the speakers in either test.
     
  11. R!f@@

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    Apr 2, 2009
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    Then I think you have a muting issue. U need a DMM and some time to settle down for further tests. U might need to dismantle it more as per service guide for access to solder side of the PCB

    No static from the speakers is a good thing and no white noise tells you that the resistor noise is still within tolerance levels, what ur problem could be minor.
     
  12. BlackSoldier

    Thread Starter New Member

    Jan 18, 2011
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    Ok...thats good news that the problem may be minor. I do have a Digital multi meter, so I will have to try and take it apart so I have access to the solder side of the board. Which board do I need access to? Thanks so far for all your help.
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Go through all the test points as per the manual and let me know.

    U should read the manual thoroughly. Find out the test points and measure the DC voltages at each point and compare them to the schematic.
    Note 'em down and let me know.
     
  14. BlackSoldier

    Thread Starter New Member

    Jan 18, 2011
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    OK R!f@@, I am reading over the manual now so hopefully I will get a chance to work on it this weekend. Thanks.

     
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