Bad CCfL Tubes

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  • xtraelectronics
    Member
    • Apr 2009
    • 49

    #1

    Bad CCfL Tubes

    I just recently repaired an ACER1916W. The Caps and circuit all checked out ok. The monitor would be on for the typical 5 seconds, then black. I determined the CCFLs to be bad. Then I discovered the return wire on the top tube was loose. Poor soldering, so I resoldered the lead wire, and shrink tube, just like original. This corrected the problem. -Until everthing was put back together. Took it all apart again. Bottom tube was acting up. Could smell ozone when it was running. So I stripped off all the shrink tube, and resoldered all connections, along with new shrink tube. Put it all back together, and success! The inverter was shutting down due to leakage current @ the tubes' ends. This was very tricky to find, and might have made the monitor appear "unrepairable". It was very frustrating, but worth it.
    I have found several monitors with CCFL issues that were repairable. If the monitor appears to run fine with "test tubes" (I keep a set of tubes on the bench to check the inverters), then perhaps the tubes are "leaking". Signs are a funny smell (ozone), and/or a crackling/buzzing sound coming from the tubes. I am suspicious of the failures of the Benq's being caused by this. Further testing on the bench will yeild more details. (I have several Benq's here to look at).

    Just my my 50 cents.
  • kc8adu
    Super Moderator
    • Nov 2003
    • 8832
    • U.S.A!

    #2
    Re: Bad CCfL Tubes

    yes this happens.
    just fixed a free 27" audiovox lcd tv with a bad joint on a ccfl.would run fine for a while and drop the backlight.tapping it just right would trigger it too.found it by poking around with a plastic tool.poke ccfl return wire and pssst shutdown.

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    • xtraelectronics
      Member
      • Apr 2009
      • 49

      #3
      Re: Bad CCfL Tubes

      Update:

      Tackled one of the Benq's today (FP731). Initially, it would power up, display for a few seconds, (very bad pinkish/red tint to it) then shut down, green light still on. Upon disassembly, found 6 bulged caps on the inverter/ PSU. Replaced them, and resoldered the inverter section. Monitor now runs without shutdown. Still had pink/red tint. CCFL tubes were shot.
      Had another dead monitor, (T705), so I exchanged the entire screen assembly, it now works perfectly! I will likely repair the PSU from the T705 for use later. I have several of these PSU/ inverters with spare parts, such as transformers, etc. if anyone is stuck, contact me. (Most of the 5707 transistors are gone). -Better to use new ones anyway.

      Dan

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