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Missing Resistor Value on LCD with Microcontroller

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

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  1. csmith


    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

    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


    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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