42LG50 no backlight

[Dgtech]

Re: 42LG50 no backlight

You should be able to get that fuse online (digikey). Radio Shaft does not carry stuff like that. The fuse should be very cheap in price so buy maybe 5 just in case. Make sure when you order to get exactly what it calls out for on the board. (3A, 63V)

Just to let you know, if you short out a cap and see the little fireworks, usually there are no problems. The negative side of the cap is ground and shorting the cap's positive side to ground is a way of discharging a capacitor - not the best way but it works.

[torpex505]

Re: 42LG50 no backlight

I'll get some on order in the next few days. After I get them installed, I will post back.

Thanks

[torpex505]

Re: 42LG50 no backlight

Ok, so I replaced the two bad fuses I'm not getting any voltage to the lights that lead to the bulbs. I'm not sure what that row of larger chips are, but there is 24v going into two of the four leads, but none out. The bottom two on the main inverter only have 24v going into one on each. Should these be passing current? I'm not sure what else to check.

Thanks

[Dgtech]

Re: 42LG50 no backlight

After replacing the fuse, did it blow again? Check the fuses again and post back. We'll go from there.

[torpex505]

Re: 42LG50 no backlight

Sorry, I should have posted that the fuses were replaced and seem to be working properly. I get 24.6~24.8 on both sides of each. Now I'm lost as to why none of the wires that lead to the bulbs don't have any voltage. I notices that on the main inverter the transformers have voltage going into them, but not out on any. Also, all but two of the transformers have 24.7v going into two of the contacts. The other two transformers only have 24.7v going into one lead.

Thanks

[Dgtech]

Re: 42LG50 no backlight

Also, all but two of the transformers have 24.7v going into two of the contacts. The other two transformers only have 24.7v going into one lead.

Thanks

You might have an open transformer. With power off of the unit, measure the resistance across the primare (input) of the transformer. Post back the result.

[torpex505]

Re: 42LG50 no backlight

Sorry I've been really busy lately... Which transformer should I test? Or should I test all of them individually and post all results?

Thanks

[torpex505]

Re: 42LG50 no backlight

Ok, I checked all transformers, and they all tested ok. I'm not sure where else to go with this one.

[PlainBill]

Re: 42LG50 no backlight

Ok, I checked all transformers, and they all tested ok. I'm not sure where else to go with this one.

I would like high resolution pictures of the top and bottom of the inverters. Knowing the part number of the inverter controller IC would be a good starting point. Depending on your skills, replacing the inverters may be the only practical solution.

Also, please verify the model number of the TV. There appears to be several variations of this TV.

PlainBill

[torpex505]

Re: 42LG50 no backlight

The model on the sticker on the pack panel is 42LG50-UA. There are dual inverters, I took the best pictures that my camera is capable of, hopefully they are good enough. There is nothing on the bottom of the boards, so I didn't attach them. Here are the pictures of the top of the main inverter. I took the pics in sections to get as close and clear as possible. Thanks.

[PlainBill]

Re: 42LG50 no backlight

The model on the sticker on the pack panel is 42LG50-UA. There are dual inverters, I took the best pictures that my camera is capable of, hopefully they are good enough. There is nothing on the bottom of the boards, so I didn't attach them. Here are the pictures of the top of the main inverter. I took the pics in sections to get as close and clear as possible. Thanks.

What is the part number of the 20 pin IC?

PlainBill

[torpex505]

Re: 42LG50 no backlight

I'm assuming thats the chip above the grounded mounting pad in the second pic? if so, it reads:
OZ964GN
T14932.2T
0746C

[crepiduse]

Re: 42LG50 no backlight

Just curious, have you checked all your 0ohm SMD resistors for their links? It sounds like you have one lead of 24v that is not flowing. Trace the leads back to find where they stop at and it will probably be a fuse that you missed or bad cap or similar.

[torpex505]

Re: 42LG50 no backlight

Should I try to trace with the unit on, or test resistance while off?

[crepiduse]

Re: 42LG50 no backlight

I'd check resistance while off first, then voltage flow backwards while on to find where the 24v is dropping off at.

[torpex505]

Re: 42LG50 no backlight

Ok, I checked the resistance of all the resistors that I could find. They all measured ~.51 when measured at 20k. I turned the TV back on to trace the voltage drop, and the drop is gone. I get 24.7 at all 20 points on the transformers.

[crepiduse]

Re: 42LG50 no backlight

Cold solder joint maybe..... is the backlight still not working?

[torpex505]

Re: 42LG50 no backlight

no, it's still not working. I tried looking for cracked solder, but I couldn't find anything suspicious...

[Hobby 1]

Re: 42LG50 no backlight

I worked on an LG, slightly different model, with no backlight, not even a flash on power up. Turned out to be the T-con board. A bad one will prevent the lamps from turning on. Quick test, disconnect the signal cable from the main board to the T-con board. If the lamps light, it's the T-con board.

[torpex505]

Re: 42LG50 no backlight

I worked on an LG, slightly different model, with no backlight, not even a flash on power up. Turned out to be the T-con board. A bad one will prevent the lamps from turning on. Quick test, disconnect the signal cable from the main board to the T-con board. If the lamps light, it's the T-con board.

That's exactly what this one is doing, no flash of light at all, did the LCD still display picture? I have not connected any kind of video source yet, but I can see snow and menu boxes when I put the flashlight to the display. I will try it tonight and post the results.

Thanks