Power Issue

edited November 2016 in Troubleshooting
My LXR stopped working a few weeks ago after a storm, lightning took out one of our modems and I guess maybe also my LXR...? Either way, it seems like a power surge occurred. I've been scratching my head as to what happened. All the test points seem fine. Finally I decided to check the mainboard. The voltage regulator and main chip get really really hot when it's turned on. I removed the mainboard just to see what would happen, and the LXR as far as I can tell goes back to normal, working as it should obviously without the capabilities that the mainboard provides.

Before I go and order a replacement mainboard though, does anyone know what else the problem may be? Is it possible that there is a short somewhere that's causing the mainboard to get hot like that, and stop the unit from functioning altogether when it's attached..? 


  • No idea if this is relevant or not but the mainboard has continuity between the gnd and the 3.3v. I don't know a damn thing really so I don't trust my own thinking, but intuitively this feels like it's wrong. Correct..?
  • The voltage regulator is being fed 4.36 volts (power drops from 4.99volts down to 4.40 on the +5v In when the mainboard is plugged in) and only outputting .86.... is it possible that the LF33CV is the reason it's not working...? Why would this also cause the 7805 to overheat? There's stuff happening here that I am clueless about, but I'm interested in knowing what's happening. Also interested in solving the problem! I hope it's as easy as replacing the LF33CV.
  • Desolder the LF33CV and check if there is still a short between 3.3V and GND. If yes, then the mainboard has an other problem.
    It is normal that the 7805 gets very hot when the LF33CV pulls to much current from it.
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