How To: Repair a Devo 7 That Won't Turn Off

Discussion in 'Walkera Devention Radios' started by Sazabi, May 6, 2017.

  1. Sazabi
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    Sazabi New Member

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    Had just the same problem with customers TX few days ago. Resistors were ok. There're 2 on input: 1W and 1/2W. 1W is ok, 1/2W had slight color deviation, but measured just as normal one. Tracing pcb leaded me to MOSFET just before power regulator. It's IRLML6402 (according to SMD marking 01AH). It is triggered by few pnp and npn transistors (one of those is controlled by power switch). Burning it makes it pass power all the time just like a short circuit. No further components can be affected, because after this mosfet is 78D05 regulator, which is way more powerful and can handle much more power.
    I've replaced it and TX works as it should.
    Also, if you don't have such tiny part, you can just solder a wire between regulator input and switch ON terminal. There're few pads to solder to. On the attached picture, faulty part is in red circle, and arrows denotes wire soldering. You won't see Power Off sign with such wiring, but it will turn off TX. I'm pretty sure such power off method won't affect IC, because it works this way in hundreds of electronics. Oh, and dont forget to remove faulty part.

     

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  2. beesontoast
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    beesontoast New Member

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    That's useful, thanks. I have a Devo 8 with the same fault. Were there any other symptoms? I ask as my unit appears to be dead apart from the ever-on red LED.
     
  3. porlock
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    porlock New Member

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    Doesn't help in my case, mine was not shortened that is between G and S, but i replaced it anyway, and not surprised it does nothing, my devo7 still does not trurn off.
     

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  4. bjr981s
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    bjr981s Moderator Staff Member

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    Did you use a power adapter to charge the batteries in the Devo 7?
     
  5. porlock
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    porlock New Member

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    Dont remember, not now after replacing component, do i did it few years back, who knows.
     
  6. bjr981s
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    bjr981s Moderator Staff Member

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    The specs on the radio require the current to be limited to 25ma by the DC adapter. Anything over this will fry something in the radio charge circuit. A few have been fixed, but it's unclear as to what the damage actually entails. If you track down the charging circuit you should be able to find the damaged parts.

    All are reported as unable to be switched off after charging.

    Good luck
     

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