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Missing Resistor Value on LCD with Microcontroller

Discussion in 'Troubleshooting and Repair' started by csmith, Jul 13, 2013.

  1. csmith

    csmith

    4
    0
    Jul 13, 2013
    Hi All,

    I'm having trouble repiaring a PCB which contains an LCD temperature display board. It looks like there is a resistor missing from the board.

    The device is a generic non-branded device (vaporizer). I tried to find the make / model by matching it up on google images, but no luck.

    The part number on the LCD unit itself is ZYH-E30561-IF

    The part number on the MC is EM78P259NS018J

    I can't find a good datasheet for it.

    I was hoping to find a whole new LCD / MC assembly, but I'm having trouble with just the standalone components.

    The resistor on pin 16 is missing (R5). I can't think of when it could have come off, but there is solder on the board suggesting that something was in-fact there.

    I thought of hooking up a potentiometer and using trial and error, but I wouldn't know what to test for.

    Any ideas?

    Obviously I should just buy a new vaporizer at this point, but this is more of a learning exercise for me.
     

    Attached Files:

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,690
    Jan 21, 2010
    If the three leads connected to the three resistors are for a similar purpose (driving LEDs perhaps) and the two resistors that are there have the same value, then that value would be my first try.
     
  3. csmith

    csmith

    4
    0
    Jul 13, 2013
    Thanks so much Steve, for your advice on both of my posts.

    I guess there is no way to know it's function without a datasheet of the LCD. Here is something interesting though...

    It looks like it may not go anywhere. I'm assuming there was a resistor there because there is solder globbed on the board. But when I trace it through the system, it ends up at a diode that was never mounted. So it doesn't look like it would go anywhere.

    Do you know of anything in the manufacturing process that would result in solder globbed onto a board with no component?

    I attached a pick of R5 in my original post. I've attached to this post, a picture of where it ends up. R5 connects pin 16 on the MC, to the anode of D2, which was obviously never mounted. So maybe I don't need R5 after all?
     

    Attached Files:

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