42" LG no backlights

[cbriggz]

hey guys i am new at this but was looking for some help. I have a 42" LG lcd (model #42LG50-UA) that when i turn it on the power light flashes twice then turns blue just like it did when it was working correctly. I havent ever had any other problems with this unit and this was def. out of the blue. I took apart the back of unit and dont see any visual damage. the screen turns on for about 3 seconds and then shuts off. there is sound so was wondering if anyone can help walk me through this?
Thanks
chris

[budm]

Re: 42" LG no backlights

Post good clear pictures using GO ADVANCED/FILE ATTACHEMENT function.

[cbriggz]

Re: 42" LG no backlights

what should i take pictures of? all the boards? the back of the unit is off already.

[budm]

Re: 42" LG no backlights

The whole back of the TV so we can see how all the boards are connected together, then pictures of each board.

[cbriggz]

Re: 42" LG no backlights

ok will do when i get home from work. thanks

[cbriggz]

Re: 42" LG no backlights

here are some pics

[cbriggz]

Re: 42" LG no backlights

can anyone help?

[gilly1984]

Re: 42" LG no backlights

Have you checked all the voltages? Be careful not to touch any heatsinks with your hands when it is plugged in.

[cbriggz]

Re: 42" LG no backlights

i am new to this so not too sure where to begin checking the voltages. There is power at the main board and i see there is power to the board where you plug the components into(there is a little green light that is on). I have looked at the master and slave inverters and cannot see anything burnt or shorted out.

[gilly1984]

Re: 42" LG no backlights

Is the voltages marked on the board near these wires? (Circled)

If so, switch tv on and test all voltages.

[cbriggz]

Re: 42" LG no backlights

not sure will check when i get home and repost thanks again. If so how do i go about testing the voltage on these?

[gilly1984]

Re: 42" LG no backlights

not sure will check when i get home and repost thanks again. If so how do i go about testing the voltage on these?

Multimeter.

Black probe on chassis then check each pin with red probe. The connectors going to the inverters should be half gnd and half 24v, Should tell you on the board.

[cbriggz]

Re: 42" LG no backlights

ok thanks

[budm]

Re: 42" LG no backlights

Can you check the voltages and fuses as shown, and also good clear pictures of the area I redlined?

[cbriggz]

Re: 42" LG no backlights

i will take some close ups of that area tonight. i was looking for a small black fuse but didnt see one. will post later thanks!!!!

[cbriggz]

Re: 42" LG no backlights

Ok guys sorry it took me so long to repost had a very busy weekend. Had
24v coming off the board to the master and slave inverters. I then tested all the fuses and inspected the boards a little closer. Looks like i found the problem.... check this pic out tell me what you think. One of the little black fuses that was labeled Zero just fell off when i moved the board right were it looks burnt.

[budm]

Re: 42" LG no backlights

Can I see the front side closed up of that section to see what that connections are for?

[cbriggz]

Re: 42" LG no backlights

here is the area that you are looking at on the front side.

[jetadm123]

Re: 42" LG no backlights

Fuses are usually identified with an "F". The component that fell off is identified with "JP", which usually indicates a jumper. The "0" stamped on the component indicates zero ohms, which is the same as having a jumper wire across the two points. What's the resistance reading of the component that fell off?

[budm]

Re: 42" LG no backlights

The jumper that burnt up can be due to shorted load (MOSFET, Transformers, etc) or it has cold solder joints (lots of current flows through these jumpers).