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Roland xp-50 keyboard problem

Discussion in 'Troubleshooting and Repair' started by Radiator, May 9, 2014.

  1. Radiator

    Radiator

    5
    0
    May 9, 2014
    Hello

    I have a problem with my keyboard. The keyboard randomly turns off, and then I cannot turn it on for a while. Sometimes I can use it for 2 hours and works fine, sometimes just 5 min and it turns off. I have opened it and everything looks fine, nothing is burned. I have also replaced all the capacitors on the power board, no change. The transformer is a bit complicated. It has five outputs. 2x8v, 2x18v and common (name from wiring diagram, I think it means GND). I have measured all outputs and it shows 1x9v, 1x4v, 2x16v. Then I connect the 1x9v and 1x4v together for a second, and the keyboard powers up. The measurements when keyboard works are 2x10v and 2x16v. Does that mean that the transformer is faulty, or just that something on the power board got a little boost and powers up? Please help


    Thank you
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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

    I don't know what you mean by
    When the keyboard is dead, are all three voltages from the transformer present?

    Transformers often have thermal fuses to protect them against overheating, but they're normally one-time fuses; they don't normally reset when it cools down.

    Do you think the problem is due to something overheating? The symptoms sound like it could be.

    You could try running it with the covers off, with a strong fan blowing air at the circuit board, to see whether that stops it from failing. Also you can run it until it fails, then check for components that feel hot or smell hot.

    You can also buy "rapid freeze" spray in an aerosol can, to spray on suspect components to cool them down. This is a good way to identify the component (or at least the area of the board) that is causing it to turn off, assuming it is an overheating problem.

    I would also check for dry joints on the underside of the boards, especially the power supply board. Resolder any suspicious joints. (Google dry joint to find what to look for:
    http://www.google.com/search?q=dry+joint&tbm=isch) At the same time, check for any discoloured areas that would indicate that some component has been getting hot.

    Be careful that nothing shorts out any part of the main board. If there's a backup battery there, you could lose your stored parameters. If you have any way to back up those parameters (e.g. a MIDI dump, or copying them to a removable memory cartridge), do that before you start working on the boards. If you can't back up your stored parameters, you will be working at your own risk. Be extremely careful that nothing metallic contacts the board anywhere except where you intend it to.
     
  3. Radiator

    Radiator

    5
    0
    May 9, 2014
    The transformer has 5 outputs. All voltages are present but different from when it works. I meant that the readings from outputs are 9V, 4V, 16V, and 16V.
    When I short-circuit the 9V and 4V keyboard starts to work and the readings are different (10V, 10V, 16V, 16V).
    When the keyboard doesnt work the voltages from transformer are present but lower than should be (from wiring diagram: 8V, 8V, 18V, 18V) No dry joints, don’t think its heat problem.



    .

    Untitled-1.jpg
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Thanks for uploading that service information so quickly!

    If you're measuring AC voltages on the 12-pin plug coming from the transformer secondaries, with your black meter probe on the circuitry's 0V rail (the shield on the audio connectors, for example), the voltages you should measure are:

    1,2,3: 4VAC
    4,5,6: 4VAC
    7,8: 16VAC
    9,10: 0VAC (these pins are - should be - connected to the circuitry's 0V rail)
    11,12: 16VAC.

    I don't know why you shorted the secondaries together, and I don't think that's a good idea.

    This schematic is for the benefit of others who may read this thread.

    xp50 psu.gif

    I think the logical thing is to measure the DC outputs from the power supply board and see what happens with them, then work backwards. There are three DC output voltages: 5V, 15V positive, and 15V negative. I've marked the multimeter probe points on this diagram.

    xp50 measurements.gif

    Let us know what happens to those voltages when the unit fails.
     
  6. Radiator

    Radiator

    5
    0
    May 9, 2014
    I think I found the problem. A bridge rectifier has no continuity on one side. I have replaced it with a different one, so far it works. :)

    We will see what happens after some usage.

    Thank you very much





    bridge-rectifier.jpg
     
  7. kpatz

    kpatz

    247
    52
    Feb 24, 2014
    Did you measure it both ways? It's made of diodes, a continuity test will only show continuity in one direction. :)

    But, if that was the problem, cool, you fixed it!
     
  8. Radiator

    Radiator

    5
    0
    May 9, 2014
    Yes both ways, and no continuity both ways. I also measured a working one to see the difference.

    Thank you
     
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