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Red tint on Dell 19" M992 Monitor

Discussion in 'Electronic Repair' started by Captain Napalm, Dec 27, 2005.

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  1. I bought this monitor recetly at a boxing day sale at a great price ($10). I
    fired it up and noticed a slight red tint immediatley. Blue and green seem
    to work fine. The on screen controls won't let me get into the rgb
    adjustements (cant find any info on service mode either), and the computer's
    video card is too crummy to allow me to adjust the RGB levels there. The
    previous monitor that was connected to it, a 15" daewoo, had no color
    balance problems.

    I opened up the monitor and removed all the shielding. The only pots present
    are labeled YH YV YV-s and YH-c (or something like that) and they appear to
    be related to the deflection circuits so i left them as is. The VGA cable
    goes directly to the board at the back of the yoke, I searched for bad
    solder joints, resolderd anything that looked suspicious and it made no
    difference. This monitor is 3 years old, it seems a little early for it to
    be worn out.

    This problem doesnt change as the monitor warms up. I can live with it but
    does anyone have an idea of what i should do??
     
  2. Dave D

    Dave D Guest


    A very wise decision!
    Modern monitors tend to use digital alignment software to adjust settings,
    internal 'pots' have been superceded where possible. There's only two ways I
    know of that you can adjust engineering settings these days on this type of
    monitor.

    The first one is obvious, obtain the correct software and interface and use
    your PC to align the monitor. This is extremely expensive and not practical
    for a one-off!

    The second one is a bit of a hack. In very basic terms, to control
    engineering settings, your monitor uses a micro and a digital to analogue
    converter. The output from the d-a converter is an analogue voltage level
    between 0V and 5V. This is used to control the circuit in question. In your
    case we are interested in the red level. Somewhere on the crt base PCB there
    will be a way of controlling the red background/drive level and this control
    voltage will be present.

    What you need to do ideally is to find this d-a output which controls the
    red level and cut the pcb track. This will mean the D-A converter now has no
    control over the circuit in question. Fit a small pot with the wiper going
    to the the track which leads to video circuits, left leg going to ground and
    the right to the regulated 5V line. Adjusting this pot will theoretically
    give you full manual control over the circuit in question.

    The problem is that without a schematic and a bit of experience you will
    have to be very determined to find the correct control line- there are many!
    It might be as simple as looking up the datasheet of the video IC on the crt
    base and seeing if it has control inputs for RGB levels.

    If you don't have any experience with monitor or TV repair then I strongly
    advise you not to attempt this yourself. It's easy to make a mistake when
    making modifications of this nature, and it's possible to destroy the
    monitor or yourself in the process!

    The red tint could be down to an ageing crt or a failed\out of tolerance
    component. Making adjustments for an ageing crt is fine and perfectly
    acceptable, but doing so for faults is not. The root cause of the problem
    must be diagnosed before making adjustments.

    Dave
     
  3. That hack sounds interesting. I am wondering though, can I not put the put
    inline with the red output that comes in through the SVGA cable? With
    componsite, a lower voltage will present will a darker picture, and since
    the red output is labeled on the board and easy to get to, perhaps I can
    just desolder the SVGA red before it gets to the board and place a pot
    there?

    Not a big problem for me, I have a lot of training in electronics including
    TV repair as it may be required by my employer.


    True, I will test various resisters and diodes next time I am in there. I
    read this one message posted by a tech that picture tint in dell monitors is
    notoriously caused by a particular IC (i cant remember which one, or if this
    monitor has it), but I'm not going to go through the trouble of aquiring a
    replacement if i can hack it to work. Its only on a second computer anyways.
     
  4. Dave D

    Dave D Guest

    It might help, but if the picture has an overall red tint then that
    indicates the black level has too much red, which won't be helped by
    reducing the red input level.

    Also, adding a resistor will upset the 75Ohm impedance match between the
    video card and the monitor, which may give undesirable results.

    Dave
     
  5. Your right I never thought of it like that. Upon closer examination, it
    looks like even parts of the screen that are illuminated but not actually
    drawn by the video card are still tinted red, so my version of the hack wont
    be effective. I think I might just have to start at the red gun and trace
    back every component that I'm able to test back to the cable. It shouldn't
    take long as the board is small and there arent very many components on it.
    Failing to find anything wrong, its ICMaster.com to start looking up
    pinouts.
     
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