Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: Davy on February 29, 2020,15:12:26
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Hitachi L22DP03U No back light. "Super picture just went off" the man said.
To check the back light I used a off-board 12V inverter they worked, I then powered the TV up with the off-board inverter the picture was perfect... OK, I know the CCFL sense and dimming circuit isn't connected... is it the inverter, the power supply or the main board I ask?
When I connect the CCFLs back to the power supply board (17IPS125-4) and leave one of the connectors out I get the slow blink - no back lights.
Are the CCFL's on the verge of failing? There were no indications that they were, no tinting or flickering, the inverter does produce momentarily at the plugs, I changed the leccy lytics and the 2.2pF disc caps, so whats shutting the inverter down, has anyone any clue's?
Dave
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Hi Davy,
I'm of the opinion that you have faulty backlight LEDs. Your external 12V LED driver will not sense a faulty LED or LEDs, hence will not shut down the backlights as the TV is designed to do. Sometimes just one faulty LED will do it. I'd say 50% of my repairs are caused by faulty backlights. They don't call me "the panelbeater" for nothing. Bruce
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They're CCFL's Bruce.... that's what I was thinking, reason I posted was I was hoping there may be another reason, the CCFL's I guess is the first thing to swap.
I can understand a cracked tube would suddenly go, I've had that where they burned at the end, this one just give up while watching and giving a super picture, no tinting or flicker just went poof', off it went... it's this that created my uncertainty - I always thought there were warning signs.
Thanks for replying, all the best. Dave
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Ah, CCFLs - my apologies. OK, so on the original inverter, compare the resistances of the drive transformers, especially the secondaries.
If one shows a difference to the rest, that may be your problem, Bruce