Problem with the 5v to 3.3v regulator



  • I'm having a problem with my duet wifi, it just started right after upgrading to 1.19beta, not sure if it's just an coincidence. When I turn on the board(even with nothing connected), the 3.3v green light turns off after a few seconds. After some investigation, I found the problem is with the TC2117-3.3VDBTR 5v to 3.3v regulator, it gets really hot in a few seconds and stops working. If I place a block of metal on top of the chip to cool it, it would work as long as metal is cool. Before I try to replace the chip I just want to know if the problem is caused by the chip itself, or some load(I have nothing connected, could there be a short somewhere) on the 3.3v that overloads the chip. Any idea?



  • After some more investigation, I found the resistance between the +5 and ground is only 10 ohms. So I guess the TC2117-3.3VDBTR shorted internally that's why it gets so hot? I'm surprised it still works with cooling.


  • administrators

    That does sound like a very odd failure mode.



  • Looks like the problem is indeed caused by the TC2117-3.3VDBTR chip. I removed it and the resistance on the chip between 5V and ground still measures 10 ohms. With a external 3.3v source connected to the duet wifi board, everything works fine without generating any excessive heat. Now I just hope I won't make too big of a mess soldering on a new one.


  • administrators

    If you've removed the old regulator without damaging the PCB traces, you've done the difficult bit.


 

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