Jvc lt-50c750 2 Seconds To Black

[Ukdigger]

JVC LT-50C750. Power board Vestel 17IPS71

TV shows the JVC logo for a couple of seconds and then no picture. I thought it would be the same fault I had with a JVC LT-50C550 where 3 LEDs had failed but the strips seem to test ok individually, 4 lots of 7 LEDs, middle strip has 8 LEDs and 3 connectors, half of them light up with 2 connectors 14.6v and the other half light up with different 2 connectors 14.6v. When I test the LED strips with a tester they read 90.2v and 68v. If I plug them back in and start the TV it works perfect all day until it is switched off for a period of time and then it won't work until I repeat the LED testing again. I would appreciate any help you could give me.

LED Strip voltages
1 19.1v
2 19.1v
3 19.1v
4 14.6v
4 14.6v
5 19.1v
6 19.3v
7 19.3v

[Diah]

Re: Jvc lt-50c750 2 Seconds To Black

at time it work perfectly as you described the way... turn down the LED BL less than 30% and see if next start are fine.. if yes rework BL sockets and test LED each one with DMM diode mode

[Ukdigger]

Re: Jvc lt-50c750 2 Seconds To Black

Before I took it apart I set the back lights at 50% and the voltages at the power board LED output were: black wire 1 79.4v black 2 12.6v and red wire 13.1v
With the screen disconnected, the tv comes on for 2 seconds goes off and then if I start it with the remote, it comes on for 2 seconds goes off and then after 5 seconds it comes back on and stays on.

[R_J]

Re: Jvc lt-50c750 2 Seconds To Black

You have a bad led strip, you already proved it with your tester, You have the same amount of led's (25) on each half but a different voltage. If your tester supplied more current you would likely see which led is failing

It looks like the second picture, the row of four are not lighting as bright as the rest.

[Ukdigger]

I managed to crack the screen on the TV so it was scrap and I left it thinking I would sell the boards on Ebay. I bought an Hitachi 50HYT62U for £15, it was totally dead but the seller said the screen was good so I thought I would risk it knowing I could sell the parts for a profit If I couldn't fix it. Three of the diodes tested short so I cut the legs out of circuit and found that just the middle one was short. With them all out of circuit the fet under the heat sink tested short as well. I noticed that the power board on the JVC was exactly the same model and part number so I tried it in the Hitachi and it came to life again with (no signal) on the screen. I couldn't get any menus working so I compared the two TVs and found that they are identical apart from the main board and T-con board, the screens have matching numbers and even the bezels are interchangeable. I put the JVC main board and T-con board in the Hitachi and used JVC bezel and stand. I now have a working JVC TV.