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JVC LT40C540 BLUE LIGHT

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kennyc:
Hi Bruce and Turnip,got new power supply board tried it in one of the TVS and it worked . Turned it off at the wall and back to the blue light again . Found if I discharged all the caps on the new power supply and turned it on at the wall then I can use the remote to turn it on and off . Its only when you turn it off at the wall it wont come back on again but if I discaharge the caps and turn it on it will come on .  When its on the voltage going to the LEDs is 69V so not much diff from when its in stand by . Thought maybe the LEDs were faulty . Took screen apart . Be careful if you do because they glue the top part of the screen to the casing. Checked LEDs all OK . There are 4 strips of 6 and 4 in a row so there are 40 LEDs. So am back where I started ,dont know if I have a faulty new board or a duff main board. Tried new power supply in other TV and still got blue light on that one suspect the  main board . Totally wasted Sat afternoon when I could have been watching the golf and not a penny made either . Dont know if you have any other ideas,  thanks

Turnip:
Hi Kennyc,

Out of interest, how are the backlight strings connected so that 69 volts fires them up ? Also when in S/by when 69 v is still present, are the backlights alight ?

Guess 40 Leds at 3 volts and a bit could equal 69v if wired in series parallel.

At least you had 'something for the weekend' - Chris.

downunder:

I find the LED-strip tester will give you a clue if all of each strip is in series or series-parallel. So a series strip of 10 LEDs will give a volts reading of around 30V, but I'm coming across more sets where the strip has say 2 by 5 LEDs in series and this pair is paralleled. The reading will now be 15V. Also 6V LEDs have hit the market to confuse us even more. - Bruce

kennyc:
Hi gents,there are 2 wires going into the 4 strips . One strip is of 6 lights on the left then a plug and a space of an inch then a strip of 4 . The second strip is the same but the strip of 4 if first then the one with 6 on it. It seems to be the one wire feeds the 2 strips at the top and the other wire goes into the bottom 2 so each feeds 20 LEDs. Hope that makes sense . The problem comes when you try to take the screen apart ,normally you just take the screws off and gently lift it up but with this one the screen is glued at the top so you have to release the cables at the bottom and lift the screen and have to get a knife and cut the glue to get into the screen . The screen is not lit when there is only 60V there . When it was working there was 58V in stand by and 69 when the screen was lit. Only diff I found in the voltages apart from the LED voltage was when the TV was working there seem to be 4 points to measure voltages at the plug at the bottom . They are 5V ,12V and 15v thats when faulty . The only diff when working is the 15V goes to down 12.5V . Can only assume its the main board

kennyc:
An update to an update .Have now got TV working . If I turn it off with the remote and have the red stand by light on it I can unplug it from the wall and plug it back in  it comes on with the red stand by light and I push button on remote and it works. Problem is if I unplug it while the TV is working it only comes back on with the blue light and will not work without fiddling around with it again . Will just have to explain to customer not to unplug TV from wall and use remote to turn on and off

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