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stereo capacitors

Discussion in 'Troubleshooting and Repair' started by mountaindew, Sep 3, 2014.

  1. mountaindew

    mountaindew

    29
    1
    Sep 2, 2014
    can someone tell me if these capacitors are bad.I have no power to my receiver.I have power to the board but thats it SDC11109.JPG SDC11111.JPG
     
    Last edited by a moderator: Sep 3, 2014
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Hi there and welcome to Electronics Point :)

    Are you worried about the two big electrolytics with the brown goop around them? It's probably just a kind of glue they use to hold it to the board.

    It looks like there may be some discoloration on the underside of the board but it's hard to tell with the pictures so out-of-focus. Can you upload some clearer photos of both sides?

    The electrolytic that's a bit smaller than the two main ones looks like it may have a problem. A clear photo would help here too.

    Are there any fuses on the board? If so, check them visually, or with a multimeter on continuity or resistance range.

    What test equipment do you have?

    Edit: Also, what make and model is your receiver?
     
  3. mountaindew

    mountaindew

    29
    1
    Sep 2, 2014
    There are no fuses.The brown goop is what I was looking at.I dont have much in the way of test equip.The stereo is a Kenwood KC-993.I hope these pics are better
     

    Attached Files:

  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    I've found a sevice manual, but you're going to need at least a multimeter to diagnose it. You can pick one up for under $20. Actually you can get one for under $10 on eBay. They won't be very good quality but they're adequate.
     
  5. mountaindew

    mountaindew

    29
    1
    Sep 2, 2014
    I can get a multimeter from my buddy.Not sure how to use it but I can try
     
  6. mountaindew

    mountaindew

    29
    1
    Sep 2, 2014
    Kris,like I said I checked the power were the 110 comes into the board.I stuck a current tester on the 2 solder spots on the bottom of the board and I was getting power
     
  7. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Be careful with your designations.

    Current = Amps and will tell you how many Amps pass through the meter. This is only reliable if you interrupt the normal path of electricity and cause it to pass through the meter.
    Testing voltage on the other hand can be done without needing to modify the device or circuit to redirect electricity through the meter. You just do as you did in the above post and the meter will tell you how much voltage exists across the two probes. Usually the black probe is connected and left on the ground or negative connection on the circuit as the red probe is moved around to probe the circuit.
    This can be helpful for testing fuses... You can alternatively put the red probe on each side. If there is a voltage on one side, and the voltage on the other side is 0 or different, it could be a good indication of a fault.
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    OK, but the rest of the unit is dead? It could be the thermal fuse, which is shoved inside the transformer. If the transformer gets too hot, the fuse opens and stays open, and you have to replace it.

    Unplug the unit from the AC mains, and measure the resistance across the two pins of the mains plug, using the multimeter set on ohms (Ω) range. If there are several ohms ranges, use the 2kΩ range. If the meter shows "1. " or something like that, the same as it shows when the probes aren't connected to anything, then it's very likely the thermal fuse.
     
  9. mountaindew

    mountaindew

    29
    1
    Sep 2, 2014
    Thank you.I will have to try that tomorrow.Does it show a fuse in the transformer
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Yes. It's not a normal cylindrical glass fuse. It's a thermal fuse. It is marked with its rated temperature, 135 °C.

    KC-993 transformer board.png

    It may or may not be replaceable. Once you've confirmed that it's open circuit, you can start unwinding the tape off the transformer to see whether you can find the wires that go to it. Sometimes they're just jammed in between the plastic bobbin and the laminated metal core. If you can pull it out, we may be able to match it with a replacement.
     
  11. mountaindew

    mountaindew

    29
    1
    Sep 2, 2014
    I tested the 2 pins from the main.With the meter not touching anything I get a 1.When I touch the 2 pins I get 0.00 thats with the meter set on 2000k
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    OK, that sounds like the fuse is OK. You can try measuring again on the 2k range. You should get a low number - something greater than 0.00.

    If that's OK we need to check the voltages coming out of the transformer. Find C92 and C96 - they are the big electrolytic capacitors near where the cable from the transformer connects to the board, and measure the DC voltage across them with the unit powered up. This voltage should be at least 20V so if the meter shows overload ("1." on the display), use a higher voltage range - the 200V range should give you a reading.
     
  13. mountaindew

    mountaindew

    29
    1
    Sep 2, 2014
    Thank you very much for your help so far.I will have to check it later tonight or tomorrow.I will keep you posted
     
  14. mountaindew

    mountaindew

    29
    1
    Sep 2, 2014
    what should I have the meter set on
     
  15. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    If in doubt, you can always start high then move the setting down until you get a nice reading.
     
  16. mountaindew

    mountaindew

    29
    1
    Sep 2, 2014
    what I mean is on the meter there are different settings.What should I have the dial on
     
  17. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    If you are attempting to check for a value for the transformer while the unit is off like you had before. Kris had recommended the 2K range for resistance.
    If you are wanting to measure those capacitors, set your meter to Voltage (DC) in the 200V range.
    If either reading is 0, or a very small number, you can set it lower and try again... ie, from 2K on resistance to 200 and see of the value is something easy to read. or from the 200V to 20V on voltage for the capacitors.
     
    KrisBlueNZ likes this.
  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,191
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    Jan 21, 2010
    Just getting back to the brown stuff between the caps...

    I can't actually view the images at a large enough size to tell by looking, but a general rule is to poke it with a screwdriver or a millimeter probe. If it feels rubbery and resilient, it's probably glue. If it is crumbly or wet or oozing then it probably shouldn't be there.
     
  19. mountaindew

    mountaindew

    29
    1
    Sep 2, 2014
    Thanks for the reply's.For the reply on #17 I am checking the 2 caps as mentioned on reply #12 with the power on.I am not too familiar with the meter so I just need to know what the dial should be set on when testing with the power on
     
  20. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Your questions are already answered on this thread; that's why I didn't reply to post #19.

    1. Regarding the resistance of the primary of the mains transformer.

    In post #11 you said you measured 0.00 with the meter set on 2000k. That's the wrong range; in post #12 I said that you should use the 2k range. That could be marked 2000 or 2k or 2kΩ, but not 2000k.

    2. Regarding the voltages across the electrolytic capacitors.

    In post #12 I said to measure the "DC voltage" across the capacitors. Therefore you set your multimeter to a DC voltage range, in a section that's probably marked "DCV" on the selector switch. Also in post #12 I said that the 200V range should give you a reading. In post #15 and post #17 Gryd3 explained that if the meter shows a reading of 0.00 or a small number, you should choose a lower range.

    For example, when the meter showed 0.00 on the 2000k range, you should use a lower range. That would be the 200k range. If the number is still zero or small, use the next range down, which would be 20k, and so on. If you go too far, the display will show "1 ." or something similar, which tells you that the range you've chosen is too low. So you go up one range. This will give the most accurate reading.

    This applies with all ranges, not just resistance.

    The multimeter will not be damaged by overvoltage though. So just set it to any range on the appropriate section ("Ω", "DCV", "ACV", whatever) and go from there. If the display is zero or a low number, go downwards in ranges. If it's "1 .", go upwards in ranges.

    Current ranges are a bit different. We haven't needed to use those yet, but we may do in future. If you upload a photo of your meter, I can give you details of how to use it to measure current.
     
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