LG 55LS4500 Sound but no picture

[RogueCapacitor]

Hi all,

I have an LG 55LS4500 that has sound from an HDMI source but no video.
The backlight turns on but there's still no picture.

I was wondering if someone could point me in the right direction of what to measure and where?

I did measure the TCON board and I know the fuse is shot. However, when I changed out the fuse for another one it also died... so I think the problem is in the power supply? Ideas where to look and how?

Thanks for all your help in advance.

[addytzu123]

Re: LG 55LS4500 Sound but no picture

Hi,
From your description, I can presume the following:
-backlight on and sound on equals power supply and mainboard most likely ok.
-replacement fuse tripped, means T-CON fault, excessive current draw, a short circuit probably.
I see a voltage convertor (U11 is the controller), wich creates two voltages (because of the two big inductors), and two switching transistors (Q1 and Q2 - six-leg devices - most likely mosfets).
Find their datasheets to identify the terminals and check for shorts. Do the same for the output capacitors (they too can go short)
Check for short also on C1, near the fuse, in ohms mode, T-CON disconnected.
Hope you fill find the culprit

[RogueCapacitor]

Re: LG 55LS4500 Sound but no picture

Hi addytzu123,

I was wondering, even though the mainboard is getting sound, and the power supply board is supplying power properly to the mainboard, isn't it possible that it's not supplying the right amount of power to the tcon and hence why the tcon is shorting out?

I measured the capacitor C1 and it seems to be infinite OHMz....?

I was going to buy another tcon board from here:
http://www.ebay.ca/itm/LG-55LN5200-U...30208#shpCntId

But I'm worried that if I just put it in, the powersupply is the true culprit and will just blow the board again?

[addytzu123]

Re: LG 55LS4500 Sound but no picture

Hi,
The power for the T-CON is comming from the mainboard, via the ribbon cabe.
You can do a short test, to check what voltage is arriving at the T-CON connector:
-remove the small F1 2A/125V fuse from the T-CON.
-connect the ribbon cable into the TCON, and it's screws (to have good GND)
-measure with a multimeter, the DC voltage by putting the COM probe at any point of GND (could be top pad of C1, or the pads of C162-165) and the RED probe on the top pad of the fuse F1 (F1 removed).
If you get 24 V reading, then all is fine with the PS and Mainboard.
If you get more than 24 V (much more - unlikely in my opinion-), then you can turn your attention to the PS.

Now, to clarify, you did replace the F1 2A/125V from TCON, and it tripped by showing infinite ohms when checked, right ?

[RogueCapacitor]

Re: LG 55LS4500 Sound but no picture

Hi,
I have remeasured things,

C1, I seem to get 680ish ohmz

I was wrong about F1 2A/125v tripping, but I get about 4192ohm, which seems rather high for a fuse.....

I haven't had time to try to check the PS voltage like you suggested yet, but i'm going to go ahead and order the TCON in the meantime.
I'm hoping for $30 just putting in the TCON board can fix it!

I'll check back once I check the PS power supply!

[dick_barton]

Re: LG 55LS4500 Sound but no picture

Addytzu123 has suggested that you measure the voltage supplied to the Tcon board to establish whether or not it is excess and has caused your problem. Should that be the case then your replacement Tcon is going to die immediately. It is well work taking the advice given before ordering.

[RogueCapacitor]

Re: LG 55LS4500 Sound but no picture

Hi addytzu123 and dick_barton,

I tried what you suggested by disconnecting the fuse and reading the voltage across, and I get only 12.12 volts. So it's less than 24, but is it too little? Or is this the right amount that's suppose to goto the TCON?

Can I just go ahead and swap in the new TCON and see how it fairs?

Thanks in advance for all your help!

[budm]

Re: LG 55LS4500 Sound but no picture

Typican T-CON runs on 12vdc, so if the fuse is good then you should have 12VDC between each end of the fuse and the chassis GND.

[RogueCapacitor]

Re: LG 55LS4500 Sound but no picture

Omg, thank you everyone so much for your help!!!
The t.v. works again!
I saved the t.v. from the landfill again! Granted it cost me $50 for the t.v. and $30 for the tcon, but still, it was a great learning experience and I proved a lot of nay sayers wrong!

Thanks again everyone!

[Shane711]

Re: LG 55LS4500 Sound but no picture

I have this TV, just got it in a few minutes ago. I suspected the T-Con board because I too have the same problem. I looked on here to confirm my suspicions. I am going to order a T-Con board and the sad thing is I had one and sold it, go figure that.

Does anyone know what goes on these T-Con boards. I am guessing the main IC.

[budm]

Re: LG 55LS4500 Sound but no picture

So the SMD fuse on the T-CON board is good? It has <1 Ohms of resistance?
You also verify using chassis as the GND ref. and your meter shows 12VDC between each end of the fuse with ref to GND?

[Shane711]

Re: LG 55LS4500 Sound but no picture

That is correct, fuse is good. T-Con board is screwed down tight. 12VDC on both ends of the fuse. Used chassis for ground. TV turns on and the screen lights up. I hear sound but no image of any kind. Just a blue screen. I just ordered a T-Con board for $18.00 but I still would like to know what went wrong. I am going to add heat pads to the replacement.

[Shane711]

Re: LG 55LS4500 Sound but no picture

Well, I got the T-Con board. And I also got another whole TV with a cracked screen. So I had a lot of parts to work with and have determined the my screen/panel is bad. The TV with the cracked screen is the same as the one with no picture so I am going to attempt to repair the one using parts from the cracked one. It will have to wait though because it looks like I am getting my own store. This started as a little hobby about 1.5 years ago and now I am moving from a 250 sq ft confined space to about 2,000 sq ft with a store front. After the move I will attempt to fix the panel on this TV.

[hoadle]

Re: LG 55LS4500 Sound but no picture

Thanks I bought T-Con board install The TV is working again
Thanks again