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Need to figure a resistor size

Discussion in 'General Electronics Discussion' started by david3264, Jun 8, 2013.

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  1. david3264

    david3264

    14
    0
    Apr 6, 2013
    When it comes to electronics, I'm basically in the First grade so was wondering if someone could help me with this. I'm installing an LCD screen in a car instrument cluster and the quality of the display on the screen doesn't look right. The contrast is off. The manufacturer of the replacement screen says contrast can be adjusted by changing the voltages coming out of 5 capacitors on the circuit board behind the screen.

    The voltages should be (Manufacture Specifications)

    V1 3.6v
    V2 2.2v
    V3 -4.5v
    V4 -5.8v
    V5 -7.2v

    I measured the voltages and this is what I go

    V1 3.5v
    V2 1.95v
    V3 -4.83
    V4 -6.32v
    V5 -7.69v

    I'd like to add resistors to v2, v3, v4 and v5 to bring them closer to the the "spec" voltages but not sure which value of resistors to add in order to bring the voltages more in line. V1 seems to be OK but the others are probably the ones giving me problems. Anybody know the resistor values needed or an elementary way for me to figure them out ??

    Thanks in advance
     
  2. Externet

    Externet

    754
    164
    Aug 24, 2009
    Do not do any installation of resistors. The observed readings are within reason.
    Just select another jumper or solder bridge to a nearby value, up or down. Exact voltages are not necessary.
    The selections change slightly the optimal contrast angle for a given view position.
     
  3. david3264

    david3264

    14
    0
    Apr 6, 2013
    Just select another jumper or solder bridge to a nearby value, up or down.

    Ok, remember, I'm a first grader. :) There is nothing else to adjust or select that I can see. I'm following the instructions of the LCD screens manufacturer but they never gave a way to calculate what value was needed. I understand they don't have to be exact but apparently, according to the maker, they need to be closer.

    Currently the display looks absolute crap regardless of viewing angle

    Thanks for the reply.
     
  4. Externet

    Externet

    754
    164
    Aug 24, 2009
    V1 to V5 are likely points to select by one jumper or solder bridge; look closely how one of them is functional and the others not.
    If the display image is bad; you may not be able to correct the viewing angle, the problem can be of other nature.
    V1 to V5 are usually to select the viewing angle, no other image quality improvement; but I may be misled. Any chance for attaching a picture of those capacitors area on the board ?
     
  5. david3264

    david3264

    14
    0
    Apr 6, 2013
    Sorry, had a small family crisis pop up.

    I hope this works. If it does there is a pic here and the V1 through V5 are located right in the center with V1 the lowest one. I guess they should have been called C1, C2, C3 and so on since they're capacitors but I was just going by what the LCD manufacturer was calling them. As you can see these caps are connected to the clip that holds the end of the LCD screen. You can just see it along the bottom edge of the screen.

    I really appreciate you guys helping with this.


    [​IMG]
     
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