42LG50 no backlight

[torpex505]

Re: 42LG50 no backlight

Well, I ended up just buying an entire power supply card from ebay for $30. When I get it and install, I will post results here.

Let us know how it goes. If the new Power supply card does not work, it looks like you just need to follow Section 1 of the Troubleshooting section of the manual on page 14.

Good luck.

[dietzcj]

Re: 42LG50 no backlight

I do know where P700 location is located.
Is that at tha part where the inverters are plugged in ?

[torpex505]

Re: 42LG50 no backlight

I do know where P700 location is located.
Is that at tha part where the inverters are plugged in ?

Good point, after looking in the service manual, I could't find it either. I'm thinking it may be a typo. I'd check the P1100 Located on the bottom left of Page 27 under PPWER. If I remember right, this is on the top left of the power board, if not, try the other two harnesses on the top right.

[dietzcj]

Re: 42LG50 no backlight

while powered on, the 24V checked out fine on both harnesses. The 5 V checked out Okay in the red harness, but I could not get a reading for the 16V where the logic input card is plugged into. That could be because it is required (to be plugged in) to get the 16 v ?

[dietzcj]

Re: 42LG50 no backlight

Well I got the new / user power supply board and it is doing the same thing. Now I happen to think it is the input board. It makes logical sense though since all I am getting is a flashing light.
I have unplugged both Master and Slave inverters and the T-con board and it is the only thing left plugged in to the power board.
Now I need an input card, if there is someone out there willing to trade a good working power supply board for a working input board let me know.

[dietzcj]

Re: 42LG50 no backlight

It is the main input board. I bought one on Ebay for $90 and it is working.

[cadillacman]

Re: 42LG50 no backlight

atta boy!!!!! good work! Sorry you had to load up the "diagnostic shotgun " not once but twice. glad to hear its alive!

[buzzltyr]

Re: 42LG50 no backlight

I appretiate the troubleshooting hints and am glad you stuck in there and solved the problem. Congrats! Today, i just purchased a 42LG50 at a recycle place. It has no picture. On powerup, get a cycle of about 4 red lites, then steady blue. I did see a slight flash. Tried various video input types, no luck. Next step will open it up and check a few things out. Will post my findings.

[buzzltyr]

Re: 42LG50 no backlight

update: 42LG50-UA no picture, no sound. On power up, get 5 red flashes, then steady blue indication. Tried multiple video sources. Got lucky for a brief time when picture and audio came up nicely, time enough to browse the setup menu. Then picture went pink and got memory dump of some kind. Now, back to no picture, no sound. Would like to know if there is a self test mode.

[dietzcj]

Re: 42LG50 no backlight

@buzzltyr
Not to my knowledge is there a self test mode.
Can you hold up a flash light to the screen and see if there is anything on the screen ?
It sounds like you may have some dry solder some where and as the tv gets warm is it causing a crack or short in the connection.
Try re-soldering the transformers (usually where the heated solder is) on the master and slave inverters and the power board.
If your blue light is on, I would think that your power supply is good and the inverters are probably the issue.
Also try unplugging the T-con board atop the unit and then power it on.
Learn from my previous posts.

[peterbilt]

Re: 42LG50 no backlight

Hoping someone could help me. i have a 42LG50 UA. Tv goes on for 2 to 3 sec than stand by. when i try turning it on again. Red light pluses 2 times than goes on for 2 to 3 sec. and off. Now i noticed the screen on the left side is darker than the right side. But looking at the back of the screen.. i can see the lights lighting up. Now i though maybe if i disconnect the left inverter and see what happens, and theres no change. does this mean
the left inverter is bad?

[torpex505]

Re: 42LG50 no backlight

I am starting to tinker with my 42LG50 again and I believe that the issue is with the transformers. Can anyone please point me in the direction of some sort of chart or guide to cross reference the transformers on the inverter? I tried electronica-usa and digi-key, but cant seem to find a replacement part. The number markedd on the transformers is "4027L 081204 KG1-3". Thanks.

[cadiman]

Re: 42LG50 no backlight

If you have master/slave inverters that is an au-optronics panel. These have inverter issues and will have burned out ccfls. The slave inverters seem to fail the most (shorted mosfets) and are repairable. Failure I think is from bad ccfls.

I use a test inverter to check ccfls on these.



The L/G parts like the power supply hold up pretty well. The L/G inverter used for the L/G panel holds up better than the au-optronics inverters do.

It all depends on what panel you have. The ua after the 42lg50 I think has the cheaper panel (china). The same goes for 42lg30.

Remember the panel (china or L/G) will have supporting boards inverter/s and t-con, also the main board will look the same but are not interchangeable. The only board that can be swapped is the power supply.

[torpex505]

Re: 42LG50 no backlight

Mine is the UA model. I had the entire case apart at one point to rule out the ccfls. They didn't look burnt like they normally do in standard lighting ones. Will these also typacilly get the black rings around the ends also? Or is the only way to tell to somehow test them?

[dietzcj]

Re: 42LG50 no backlight

I have a power supply board still for sale on ebay labeled eay4050520 LPG42-08H EAX40157601/11.

It is only $25, plus 14 for shipping.
This was left over from my posts up above here.

Cheap.


Chris

[torpex505]

Re: 42LG50 no backlight

Thanks for the info, but I don't think I can justify buying anything else for this project.

I also got burned on an ebay deal last year and both ebay and paypal basically told me to screw myself, so I closed my accounts.

I may just start looking into led strips to replace the ccfls. I'm just trying to determine if that would be worthwhile, considering I'd have to have a second powersupply to run the leds that I would have to manually turn on and off with the TV.

[dietzcj]

Re: 42LG50 no backlight

Okay

[equineent]

Re: 42LG50 no backlight

This looks like the same setup as the magnovox inverters I have worked on. in my experience, they either produce no backlight, or maybe a flicker of a backlight before going out.

its almost ALWAYS due to a faulty transformer. you MUST pull all transformers, one at a time, and do a resistance check on all windings. keep a chart. youll find a bad one.

New to forum :I have 42lg50 UA. done all the trouble shooting on this thread. I have 24 volts up to the transformers nothing out of the transformers. Are you saying that one transformer will take the whole board down? There are 10 transformers on each board.
Thanks

[PlainBill]

Re: 42LG50 no backlight

New to forum :I have 42lg50 UA. done all the trouble shooting on this thread. I have 24 volts up to the transformers nothing out of the transformers. Are you saying that one transformer will take the whole board down? There are 10 transformers on each board.
Thanks

Not exactly. A bad transformer (or any other fault) will trip the protect circuitry, causing the inverter to shut down. Replace the bad transformer and it will work perfectly.

PlainBill

[Audioplus]

Re: 42LG50 no backlight

New Post and sounds laike a common issue, 42LG50 UA, red led circles twice around power button, then shuts down. No picture. Took unit to an old CRT repair tech, tested fuses and caps, couldn't find anything. I assume a mainboard (what I would call mainboard with A/V inputs) issue, ordered new and replaced. Now I get the Red LED circling, stays solid and switches to Blue. Have an image (can see via flashight through panel), gets snow, menu, but no backlight. Is this now sounding like a fuse or cap issue on power supply, inverter boards, any ideas? Sounds like I'm 1/2 way there, must have taken a huge power spike?
Thanks to anyone!
Dan C - Audioplus