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Discussion in 'Troubleshooting and Repair' started by mrmodify, Mar 1, 2010.

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  1. Mar 1, 2010 #1
    mrmodify

    mrmodify

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    Feb 13, 2010
    Working on power supply for a marantz 4300. Have replaced bad parts by checking with power removed. Powered up and got some strange readings (to me). I have the amplifier boards removed (waiting on parts) Got the AM section working FM is still dead. The plug on top right is outputs, The voltages do not change if connected to reciever or not. DC output pins #3 & #5 don't understand.(top right) I have written down voltages on different areas of pwr supply. Have attached schematic. Sorry for the quality. THe schematic I have here is a little clearer if you have any questions. Thanks John
     

    Attached Files:

  2. Apr 21, 2010 #2
    jerryg50

    jerryg50

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    Apr 18, 2010
    I don't exactly understand what your question is. This power supply is a complex type analog type supply using current and DC sensing.

    For example, if the output stage has a fault condition this supply will go to protect. If something in the unit is pulling too much current the power supply will go in to protect.

    There is also a very stable type feedback circuit for the DC reference. If something is not exactly correct with this area the output voltages will be out of spec.

    Jerry G.
     
  3. Apr 21, 2010 #3
    mrmodify

    mrmodify

    157
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    Feb 13, 2010
    Thanks for reply Jerry G. Read your reply. My biggest problem is I don't really understand schematic. I am trying to learn. Is it possible that I am getting strange voltages because power supply is not sensing a load since outputs are out of circuit. The voltages I am concerned with are the base of H802 and collector of H803 voltage should be 36.5V I am getting 14V. Also with collector voltages on H806 & H807 I get 51V schematics says .7V.
    Thanks again John
     
  4. Apr 22, 2010 #4
    Resqueline

    Resqueline

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    Jul 31, 2009
    What are the voltages on base & emitter of H803? Collector voltage will be a consequence of this.
    The b-e voltages are crucial to wether the transistor should be conducting or not.
    H807 is clearly shot, having 11V on its base. Anything substantially over 0.7V tells you it's broken.
     
  5. Apr 23, 2010 #5
    mrmodify

    mrmodify

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    Feb 13, 2010
    Hello Resqueline, H803 base = 7.8v. The emitter = 7.2v. I have tested all transistors in the power supply with transistor checker in and out of circuit. I will check or just fo ahead and replace H807. H806 base = 4.8v collector = 50v emiter = 11v. I am going to ask stupid question. How did you get H807 is shot. Thanks greatly for you reply. John
     
  6. Apr 23, 2010 #6
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
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    Jan 21, 2010
    The connection between the base and emitter -- in one direction (forward) -- should never be above (around) 0.7 volts.

    The emitter has a little arrow on the symbol. The arrow points from +ve to -ve when the Base-emitter junction is biased forward.

    In this case, you measured voltages of 11V and 0V for B and E respectively. Note that the Base (E) is 11 volts more positive than the Emitter. Referring to the circuit diagram, you can see the arrow on the emitter points away from the base -- the voltage at the base is 10.3 volts higher than it should ever be.

    Note that there is an alternative explanation. It may be that the connection to the emitter of H807 is broken (sue to a poor solder joint perhaps). It may be an idea to look at this, and re-solder it (it should require no more than a brief touch of a soldering iron) if it looks dodgy. Then re-measure the voltage and see if anything has changed.

    Another possible problem is H806. It shows the Emitter as 6.2 volts more positive than the base. This is the reverse direction (note that the arrow points to the emitter and that end is more positive). In the reverse direction, one should not see more than a few volts as the Base-Emitter junction can be damaged if this exceeds a very small voltage (around 6 volts is common). This junction is almost certainly in "breakdown". It does not mean the transistor is being damaged (if the current is low), but it's not a happy state for the transistor.

    The base of H806 should be around 0.7V more positive than the emitter, or around 1.4V above ground. Lower values are OK as it means these transistors are turned off.

    If it is relatively cheap to do, I would consider replacing both transistors. If the second turns out to be faulty, another visit to the store will cost you far more than the cost of the transistor.

    It looks like the collector of H805 is connected to the base of H806. The odd thing is that you show 2 different voltages for them.

    What is more odd is that you show 0V on the base of H805 when the base seems to be biased by a couple of resistors from a point measured at 25V. On that point. The connection "2" measured at 25V seems to be a control input that enables or disables the output on connection "3" (alternatively it may regulate it)
     
  7. Apr 23, 2010 #7
    mrmodify

    mrmodify

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    Feb 13, 2010
    Thanks Steve, I will sit down tomorrow and study schematic to follow what you are saying. Replacing H806 & H807 is not a problem. Will resolder joint on Emitter of H807. I will make sure of differences in voltage for H805 & H806. Sorry about schematic but voltage on connection "2" is 2.5 volts not 25 volts and connection "3" is at 50 volts. Again thanks Steve, John
     
  8. Apr 23, 2010 #8
    Resqueline

    Resqueline

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    Jul 31, 2009
    H803 seems to be doing its job as good as can be expected. Check C807 for being shorted (or measure R805, -6, & -7 voltages).
     
  9. Apr 23, 2010 #9
    mrmodify

    mrmodify

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    Feb 13, 2010
    Hello Resqueline, Electrolytic Cap. C807 was removed and checked when I found rectifier H811 open. It checked fine with capacitor checker. Voltages on R 805, 6, 7 need to be checked from resistor to ground ? What do you think they should be.
     
  10. Apr 23, 2010 #10
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
    2,820
    Jan 21, 2010
    I can't even see where the diode H811 is, and many of the resistor values are almost impossible to read.

    I take my hat off to Resqueline who was able to read C807 :)
     
  11. Apr 23, 2010 #11
    mrmodify

    mrmodify

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    Feb 13, 2010
    Schematic I have is pretty poor. I rescanned page of schematic. See if this helps any. drawings around schmatic are voltage readings I have taken.
     

    Attached Files:

  12. Apr 24, 2010 #12
    Resqueline

    Resqueline

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    Jul 31, 2009
    Googling the relevant keywords brings up only 7 results, two of which are in German describing a restoration process of the amp & psu (with pictures). Help yourself.
    The search also brought about better partial schematics which can be found here, here, & here.
    Check the PCB tracks for hairline cracks.
     
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