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DELL 17inch LCD repair

Discussion in 'Troubleshooting and Repair' started by golemmaster, Jul 1, 2009.

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  1. golemmaster

    golemmaster

    15
    0
    Jan 15, 2009
    I have two Dell 17 inch LCD screens that are not working.
    They have similar power supplys in them. Typical BenQ innards.

    One has an open fuse and four bad transistors that I'm about to replace. Power LED stays stead on. Hopefully that's it for that one.

    The other one has a good fuse and transistors. The power LED flashes. I can hear ticking from the high power section. The LED flashes in time with the ticking. Voltage in the low power section pulses with the ticking.

    I'll post a pic when I find my camera.


    What to check.....
    I have a decent multi-meter. I don't have an ESR meter. Love to have one.


    Thanks
     
  2. golemmaster

    golemmaster

    15
    0
    Jan 15, 2009
    Dell E172PFb and E173PFb

    Dell E172PFb and E173PFb
    See attachments.

    I've removed the Q743 and Q751 D10PFT06 on one model, FU9024N on the other. Best I can tell they may all be bad.
    The Q739, Q740 and Q759, Q760 C5707 seem to be good on one monitor and bad on the other. The fuse is bad on one monitor. I've checked R765 and C765 that control the frequency of the oscillator circuit in IC751. Best I can tell they are within tolerances.

    Waiting for parts and time and knowledge.
     

    Attached Files:

    Last edited: Jul 20, 2009
  3. golemmaster

    golemmaster

    15
    0
    Jan 15, 2009
    Dell E172PFb and E173PFb

    I replaced the C5707 and ST D10PF06 MOSFETS and fuse.
    Backlights work but no video. No "No Signal" box that would normally be displayed. The monitor doesn't go to sleep. I know I've read about this symptom somewhere but can't remember where and of what to suspect and test next.

    Although the fuse on one of the monitors tests good on the DMM, it seems to die when I turn the monitor on. Measuring directly off the legs of the fuse:
    Voltage ahead of the fuse 18.5VDC. 19.5+VDC behind the fuse. (strange)
    When I push the button: ahead remains 18.5VDC, behind the fuse quickly dives to about 4VDC. Voltage returns to 19.5VDC behind the fuse when I shut the monitor off. This results in a flicker of light from the backlights. I temporarily shorted the fuse leads together and the back lights turn on. Didn't check video function on that one yet.
     
  4. golemmaster

    golemmaster

    15
    0
    Jan 15, 2009
    Dell E172PFb and E173PFb

    I spoke too soon. One of the screens works fine. FIXED!

    The other with the weird fuse.... that works but does that odd thing previously mentioned. I shorted the fuse and that monitor is working too. I need to fix that and I'll be all done. Shweet

    I'm also working on a BEFSR41 router.... but that's another thread.
    ...And my AMP/Receiver. Too complicated for me but I'm poking around in it anyway.
     
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