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Water damage... tips for debug?

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    Water damage... tips for debug?

    Apparently my Magnavox MWD-2206 suffered water damage and will not power on. Right now I have to make an assumption as I don't know what the power on sequence is, but it looks like the power supply is working.

    I seem to have found a PCB track that should be floating, or at least it should rise to +5V, but stuck at 0.628 volts. It's a pull-down line with a 10K pull-up.

    That 0.628 volts is suspicious as it's close to a diode drop. Any ideas on how to debug this?

    I found the pullup resistor, and thinking about pulling it out to see how the circuit reacts (and to measure it...) It's a carbon composite resistor it looks like it's fine and highly doubt it value shifted. The wire must have shorted somewhere else, perhaps to the diode, but pulling that resistor might reveal some clues.

    #2
    Re: Water damage... tips for debug?

    Can we please get more details info as to what we are dealing with especially the PCB Track you are referring to?
    Never stop learning
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      #3
      Re: Water damage... tips for debug?

      What I see is
      +5V ----pullup resistor--------x------x------x------x--------Microcontroller input

      X is where a switch pulls down to GND through a resistor.

      Supposedly when nothing is pulling down on that wire, the microcontroller should read 5 volts... but it's not, it's reading 0.6 volts.

      I checked each of the switches and they don't seem to be shorting/leaking as when I depress them, the line does indeed go down to 0V or at least changes. So I suspect that something is bleeding into this line due to water damage...

      I'm hoping that the microcontroller input didn't end up leaky somehow, that's a possibility too. The microcontroller is SMT, temporarily pulling it is a possibility so that I can test the track, but that seems like a lot of work...


      Just wondering if there's some tips and tricks to debug this line.

      ----

      More data:

      I just found one switch that was leaking at 2.6K open and <1 ohm closed. This is a bad switch and would explain the weird behavior. I think at least this problem is now solved!
      Last edited by eccerr0r; 12-01-2016, 01:45 PM.

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