Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: kennyc on July 21, 2017,06:02:28
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H Guys, have got 2 identical TVs with the same fault . Have attatched pictures of power supply and chassis Both have a blue light at the front but nothing else works . Have checked the voltage points on bottom right of the power supply . Seem to be 5V ,12V and 15V. The voltage is 61V which feeds the LED strips with the 2 plugs either connected or not . Dont know if the fault is the power supply or the main board or the LED strips. Even though they have the same model number one seems to have Tcon board and the other doesnt. Power supply and main board have same serial numbers so the Tcon must be built into the long panel at the bottom of screen Any ideas ,thanks
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Hi Kennyc,
Suspect you have two sets with duff screen Leds. 61v supply for a 40 inch seems a bit low, so suspect inverters have cut - Chris.
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Hi Turnip ,thing is the 61V remains if I disconnect the 2 plugs that go into the screen . There is also no flash of light when turned on for a fraction of a second . Will maybe take the screen apart in the morning . Thanks for your help and ideas
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Hi Kenny,
At the connector on the PSU that comes from the main board, are you getting the BL-ON (INV-ON) signal to activate the backlight LED driver - expect 2.5V/3V.
Bruce
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Hi Bruce ,the only marking on the board is Pon and there is 5.14V on it . It seems to be the same voltage as is on the other leads marked 5V . Hav ordered another power supply but there is a burn on a FET that is next to the Pon pin so fingers crossed . Will let you know the outcome when I get the new power supply . Wont touch the screen till then. Thanks for your help
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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
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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.
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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
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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
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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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Hi Kenny,
Main boards commonly cause your problem. I've had some success with cooking the main boards in these el-cheapo sets. - Bruce
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Hi Downunder ,never "cooked " a board before . Read about doing it so will give it a try . What temp and how long do you do it for ?. Have tried heating it up with a hairdryer but makes no diff
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See post "LG 32LD490 - Suspect BGA issue" on this page. - Bruce
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Hi all
I wonder if you could help. I also have the blue light issue with my 2 year old JVC LT-40C540. When power is on I get steady blue light. Repeated powering on from mains eventually the blue light goes red and I can switch on the button on side of TV.
Sometimes after switching on mains it works as it should going straight to Red/Standby and Im able to switch on using button on side of TV
I've just replaced the power supply board (Ebay purchase) but same issue persists.
Just ordered a main board from Ebay but wondered if anyone has any advice.
(I haven't tried cooking any boards yet)
I have no electronics knowledge other than building radios from kits as a kid. Any advice gratefully received. Martin.
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in answer to my own question - I replaced the main board and it all works fine now. :)
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Not sure if this attachment is related. Found it on the net.
Bruce