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More tinkering with sick LCD

Discussion in 'Electronic Repair' started by JM, Oct 30, 2005.

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  1. JM

    JM Guest

    I've been playing with a broken LG 566 LM LCD screen I got my hands on. I
    posted about it about a week ago, and I've since replaced all of the caps on
    the main board with no change in the symptoms.
    I started poking around on the board checking voltages as best I could by
    following traces from the power input lines, and I noticed that there are a
    few caps near the two ribbon connectors that run to the actual LCD panel
    that have voltages written next to them in the silkscreen. The voltages
    written are 9.2, 3.3, 18, and -6 volts. The caps themselves are rated well
    above these values.

    Measuring between the positive side of these caps and ground with the unit
    powered on, I get nothing above 4.5 volts -- does that seem odd, or is there
    something about the way I'm measuring that would give me false readings?
    I do have good voltages at the input from the power supply, 2x5v and a
    single 12v, but since the one visibly bad cap that I replaced in the power
    supply was on the 12v line, I'm wondering if there is some component on the
    12v line of the main board that shorted or went open and is causing
    problems.

    If anyone knew where I might be able to find a schematic for this unit that
    might help me out, I'm by no means a professional tech but I like to learn
    what I can by tinkering with broken gear... especially when there's nothing
    to lose, as in this case! All I have is a DMM and some spare time once in a
    while, but I'm hoping I might get lucky and find one bad part that is the
    culprit.

    Thanks in advance for any help!
     
  2. JM

    JM Guest

    Just wanted to follow up on my post about the LG 566LM lcd screen I asked
    about a few weeks ago. Long story short, it suddenly started working on me
    one day after a few hour long visits to the freezer, but would gradually
    degrade as it was left powered up.

    I bought some freeze spray and was able to narrow the location of the
    temperature sensitive part to one region of the board. By freezing the end
    of a Q-tip and probing in that area, found a single SMD cap that, when
    frozen, brought back a nice clean picture. The cap was between pin 5 on an
    AIC1341 chip and ground, so I removed it and installed a regular old cap of
    the same value directly between that pin and a nearby ground. Works great
    now!
     
  3. Cool fault searching trick (excuse the pun).
    Must remember that.

    Bart Bervoets
     
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