LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power board?

[KhattOn]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

Can't edit I guess.... I have the same model as OP, I just want to make sure I get the correct resistor.

[KhattOn]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

Sorry to resurrect this thread but I'm having the exact same problem as initially mentioned. Could you link me to a/the 1 ohm resistor you purchased, or will any 1ohm resistor do?

[Cec243]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

Hello, I'm sorry to resurrect this thread. I have a similar issue with an 42lg5010. After reading this thread and testing the fuse on the master inverter board it seemed to be faulty. I attempted to replace it but it was too small so I just bought another inverter board off eBay. Like for like swap. Now when I turn it on the screen comes on for 2 seconds then goes off and I can continue to hear the sound. Before I changed the inverter the screen wouldn't even come on. Now I have the 2 seconds to black problem. Any suggestions on what to try next? Obviously the fuse had gone on the master and now with the new board it's ok but there's something that's making the screen switch off.
Please help I'm tearing my hair out!!!
Thanks in advance

[budm]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

@tramo, please start the new thread with the model number of your LG 32LD320 TV so we will not get confused with this thread which is for 42LG20-UM. Also upload the pictures of the TV, boards. etc.

[tramo]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

Hi Guys, I have similar problem like in this thread, therefore I don't create new thread. Problem is on LG 32LD320 backlight is off, I see that the LCD is working correct(check with light) sound is also woking(assume that mainboard). It seems that the Power is also correct on pins to inverter is correct 24V but on other pins: Error = 2.2V, PWM_DIM = 0V, INV ON/OFF = 3.3V, BRI = 0V
Is the problem truly on backlight inverter? Could you help me to how to proceed?

Thank you.

[tom66]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

The plastic bezel comes off the front to reveal the LCD panel assembly. From then on it's about 20 small screws to take the frame off, then a careful lifting of the LCD panel out of the TV. The panel is incredibly fragile, so make sure you have enough space for it to go and that it won't be damaged. Then you find the diffuser films and eventually the bulbs themselves.

[miles69]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

OK, after carefully rereading this thread it seems like bad ballast caps or CCFL. Now the question is "how to breakdown the TV to access this area". The rear panel is off and circuit boards are removed.

[tom66]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

Plasma = easy. If you get help carrying them up the stairs, that is! I need to make a jig for supporting them while servicing, like Randtek uses. Never done an IPM, but I'm getting a 50" to work on Sunday/Monday, so it'll be fun to see how that works out!

[miles69]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

I am new here so I don't know if I should start a new thread or continue with this one. For now I will continue this thread.

I have a similar problem with the same 42LG20-UM manufactured in 2009 connected to cable (Charter) and DVD (Sony) through a receiver (Sony) using HDMI.

Symptoms have been present for several months and are:

1. On start up the right side of the screen is blurry with heavy red color; left is normal

2. Clicking on the menu button shows the same problem with the menu screen.

3. White text come through clear and sharp on both sides with a slight out of focus at the far right. What should be yellow text is red on the right side and normal on the left. (Fox News has a yellow text crawl with some white text at the bottom.)

4. The top of the screen has some horizontal black lines that come and go. This is new starting about 2 weeks ago.

5. After about 15 minutes the right side problem goes away but the horizontal line problem remains.

I replaced both inverter boards. Things worked good for about 30 seconds and then the problem returned but the horizontal lines now cover the top 1/3 of the screen and are very faint.

After reading through this thread I found that F1 was open on both the original and replacement master inverter boards. I am guessing that F1 on the replacement board went out after the 30 seconds of good operation. Any ideas on what might cause F1 to blow would be helpful.

[arman960]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

yes tom66 looks knowledgeable in plasma tv. But he said he never worked with any board with IPM Y-SUS.This is my first plasma tv that I am working on. And according to copperville tv repair test it seems like my upper buffer board and Y-SUS is bad. I think palsma tv is too heavy and makes too much heat. I will never buy another plasma tv to repair. First and last one.

[budm]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

I do not repair Plasma TV at all, too heavy to work on it by myself. Tom66 is real good at it.

[arman960]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

budm, have you worked with SANYO DP42746 Plasma tv?

I am trying to repair the Y-SUS on this board.

[budm]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

Thank for posting the result, the half screen brightness make sense due to only the Slave Inverter was trying to drive the lamp without the Master inverter working.

[arman960]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

problem solved. Thanks all of you for helping me.

[arman960]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

budm, problem solved. You are genious. That black fuse was bad. I put one small thin wire to jump the resistor. But it was very difficult , because so small space. But I put extra solder to remove it just like you told me with one 60 watts soldering iron. Now I will have to order the surface mount small fuse from online.

Also I do not have the half darker screen at start-up either. Screen is bright all the way.

budm I thank you and appreciate your help. You are the best. :-)

[vinceroger69]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

I stiil do not know what the lable on the fuse means yet, it has 20 printed on it, on other board I worked on, it has '15' on it, but the silk screen next to it indicates it as 0.75A 75V. What I do is to use DMM and set it to DC Amp, then just put the probes on the two pads and take the current draw reading and add 25% to the number. I think 1A should be fine, I use Littlefuse PICOII axial-lead fuse soldered in place.

thanks for that info budm i am sure it will come in usfull

[budm]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

I stiil do not know what the lable on the fuse means yet, it has 20 printed on it, on other board I worked on, it has '15' on it, but the silk screen next to it indicates it as 0.75A 75V. What I do is to use DMM and set it to DC Amp, then just put the probes on the two pads and take the current draw reading and add 25% to the number. I think 1A should be fine, I use Littlefuse PICOII axial-lead fuse soldered in place.

[vinceroger69]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

budm i did not notice that fuse had no top solder ends like the white one also out of intrest what amp would that fuse be? (not saw selldoor on latley hope hes ok)

[budm]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

There is not much room at the end of the fuse on this black fuse, yes that black fues is BAD. This fuse doe not have top solder ends like the white fuse that you can easily solder on the top of the fuse. You can add more solder to the pads to allow you to solder small wire to it.

[vinceroger69]

Re: LG 42" LCD TV 42LG20-UM No video ONLY sound BAD inverter board or bad power boa

for now you can just jump the fuse with a piece of wire across the top of the old fuse i would probably use a piece of 3 amp? fuse wire this is only just to test you will still need to change the fuse if this works.