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Onyo TX VS373

Discussion in 'Troubleshooting and Repair' started by Q Branch, Sep 21, 2012.

  1. Q Branch

    Q Branch

    9
    0
    Sep 21, 2012
    Newbie here.
    I have an Onkyo TX VS373 that keeps burning r543. I have a schematic with the service manual in pdf. r543 is on page 37 and 38 of the schematic and is in the speaker circuit. I replaced r543 with a 330ohm 1/2 watt carbon film resistor and capacitor c509 which was burned also. When I reassembled and tested the unit it burnt again. I am not sure what to check for next.
    It may help to know how the receiver went out to begin with. My son thought he would set one of the speakers outside to listen to as he swam in the pool. He turned all the other speakers off except for the one he sat outside and cranked it up. Well didn't take long and ....silence, system shut down and would not power up.

    I will try and attach the pdf for anyone that may be able to help.
    Well the file is too large to attach. I can send it email to any one that can help.

    I appreciate any help I can get. Things are tight and I don't want to buy a new receiver.

    Thanks.
     
    Last edited: Sep 21, 2012
  2. shrtrnd

    shrtrnd

    3,676
    454
    Jan 15, 2010
    I don't have your schematic. You need to trace whatever semiconductor is feeding your resistor, it's on it's way out, and supplying too much current to your resistor.
    Just trace the circuit from the resistor and find out where that excess current is coming from. You'll need to replace that device as well.
     
  3. Q Branch

    Q Branch

    9
    0
    Sep 21, 2012
    Thanks, I checked the toshiba a1940s, there are 6 of them, two are bad- one shows 0 ohms on one post the other shows 0 ohms for both posts. I think you found it. Now to replace them both. Thanks and I'll let you know how it goes.
     
  4. Q Branch

    Q Branch

    9
    0
    Sep 21, 2012
    Actually one is an A1940 and the other is a C5197. You think radio shack has a comparable replacement?
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,221
    2,695
    Jan 21, 2010
    I'd say they are 2SA1940 and 2SC5197.

    Unless they are extremely generic transistors I wouldn't expect Radio Shack to have a compatible replacement (or if they do, it would just be dumb luck)

    Here is the datasheet for the 2SA1940. Does this look line the particular transistor? This is a PNP transistor used in the output of audio amplifiers, so I guess it matches where you're looking.

    The datasheet also notes that the 2SC5197 is the complementary NPN version. And that matches what you have.

    If both of these are shorted, I would expect that your device would blow fuses (or remain shut down).

    I recommend that you remove the transistors and re-check that they are shorted. If these are shorted, I would also check the transistors which drive them, and if these are damaged, those which drive them. You have had a failure in a part of the circuit which has relatively high voltages and quite high currents available. It is not unlikely that the failure of one part can cascade through a number of other parts, taking them out as well.

    Perhaps we should concentrate on inding the extent of obvious damage before replacing parts. As you see, if a fault still remains it can let the expensive smoke out of things.

    It might also be useful to check the speaker. It may have been damaged just before everything went quiet.

    Presuming the amplifier has multiple channels, you may be able to take resistance readings from both sides and compare them. However, since you have already found a major fault, you may not be able to benefit from this without you havinf significant skills in reading schematics as you will need to mentally determine if the already existing fault will have an impact on readings.
     
  6. Q Branch

    Q Branch

    9
    0
    Sep 21, 2012
    Thanks Steve, I will remove the parts and recheck those and look for other problems. I did locate the parts here local and placed an order. I will post any other findings later. I have checked several other transistors near the area of the burnt resistor, they have checked out OK.....so far.

    Thanks for the help. This is a great forum, Thank You.

    Oh yeah, they are parts numbers 2sa1940 and 2sc5197.
    AND I listed the wrong model, it's an Onkyo TX-SV373.
     
    Last edited: Sep 22, 2012
  7. Q Branch

    Q Branch

    9
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    Sep 21, 2012
    Help again, Got it all back together and the good news is that it is no longer burning the resistor.
    Bad news is that when you turn it on, it correctly shows power on in standby mode, hit the standby button to power on and it starts up and then clicks a relay off on the main power board.
    I'm at a loss.
    What should I check next?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,221
    2,695
    Jan 21, 2010
    See if you can determine what the relay is there for.

    I suggest it may be part of a speaker protection circuit that senses an output DC offset and disconnects the speakers.

    You will almost certainly have to go through a procedure to set up the bias current and DC offset. It is also possible that there are other damaged components causing this problem.
     
  9. Q Branch

    Q Branch

    9
    0
    Sep 21, 2012
    The relay is M903 on the power board. I would think this controls power to everything. It is before the transformer. I checked the wires from the transformer that run to the main pc board and all (red, black and brown) have continuity with the frame....? Is this right? I will lookup how to check the transformer.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    OK, it's almost certainly not speaker protection then.
     
  11. Q Branch

    Q Branch

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    0
    Sep 21, 2012
    The leads into the transformer show no continuity, but all the leads out show continuity with the frame. I read:

    " Simple Tests
    Unplug the amp and drain the capacitors before you start. Do not remove the transformer from the amplifier before you start. Remove the output and rectifier tubes.

    Identify which wires are which by circuit connection. The primary will have two (single ended), three (push pull, or very rarely single ended with ultra linear tap), or five (push pull with ultralinear taps) leads. Noting which leads connect to the B+ line, measure the resistance from the B+ lead to each plate of the output tube(s). Write the resistance reading down. Measure the other side if it's puah pull. Plate windings are almost always in the tens to a few hundred ohms of resistance. A reading much over 1K is pretty sure sign that the winding is burned open. If it's open, the transformer is dead. [There are ways to fix "slightly-dead" transformers, but this is extremely risky, and probably doomed to failure. I'm not going to write down how. Don't waste your time.]

    While you're at it, measure the resistance of every lead to the chassis. This reading should be very high, hundreds of K or preferably megohms. A low reading here indicates a short to the transformer core - again, dead transformer.

    Do a similar test on the secondaries - look for open windings, or shorts to the core. Finally, test for the resistance from primary to secondary. A low value, under a few K indicates an internal short, and a dead transformer.

    If the transformer fails any of the simple test, it's dead. Replace it. If it passes all of the simple tests, it may still have an internal short Sometimes a primary will have enough resistance that the transformer does not burn up or burn the wires in two , but will just bog down, have low power and sound bad. If you suspect that is the case and you don't have the skills to do the advanced tests, take it to a competent tech. "

    Now I am not sure about what the B+ line and all that is but I am showing continuity on the out side of the transformer with the frame...

    Bad transformer?
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,221
    2,695
    Jan 21, 2010
    Where did you get those instructions from? What is this device? Does it have valves too?

    Were you able to find a place to upload your manual to?
     
  13. Q Branch

    Q Branch

    9
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    Sep 21, 2012
    Latest info; I have disassembled the main again and found six driver transistors that have gone bad. I placed an order for and will repost as soon as I get those in. I dont think it is the transformer.
     
    Last edited: Sep 29, 2012
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,221
    2,695
    Jan 21, 2010
    Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

    The above text is a placeholder for a question the Q Branch would have ignored anyway.
     
  15. Q Branch

    Q Branch

    9
    0
    Sep 21, 2012
    Whats up with your last post Steve?;

    "This page is available, however, but because occasionally circumstances occur in which toil and pain can procure him some great. To take a trivial example, which of us ever undertakes laborious physical exercise, except to obtain some advantage from it. Or desires to obtain pain in the bullet train to find fault with in the pleasure of pain that produces no resultant good to flee. These cases are perfectly account of the system, the fault of those who are in the original text: this is to sink."
     
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