LG 42LB1DR No Video or Sound

**tom66** · 03-04-2012, 02:57 PM

Re: LG 42LB1DR No Video or Sound

Do you have a multimeter? Check the output voltages on the power supply.

**IRShifty** · 03-04-2012, 03:41 PM

Re: LG 42LB1DR No Video or Sound

Your fast, was just documenting those. Added two images to the OP. One has another picture of the PSU, the dots on the connectors are the key for the image with the chart of voltages on it. The top line on the each table in the chart represents the marks on the board and the second row is the voltages i received while testing. The top two connectors read the same, each one goes to one of the back light inverter boards (if that's the correct term).

**tom66** · 03-04-2012, 04:55 PM

Re: LG 42LB1DR No Video or Sound

3.4V seems to be your problem if it's around 1.5-1.8V. *Especially if it is rising while you take the measurements.*

But... I note this TV has a HDD and that some LG TVs with HDDs have problems powering up with a bad disk drive. (I know, stupid design, given HDDs have a fairly high failure rate.) Try unplugging the HDD power and SATA cable and seeing if it powers up properly.

Can you remove the power supply and take a picture of the underside? I will try and figure out how the 3.4V is generated. On most LG TVs it is generated using a secondary DC-DC converter and it's possible this could go bad (but I've only ever seen bad caps on those types of converters, and only once on an LG LCD.)

**budm** · 03-04-2012, 06:49 PM

Re: LG 42LB1DR No Video or Sound

"The back lights come on and stay on but there is no picture on the screen." That is the keyed words, if the backlights come on and stay on but you see no pictures, then the problem can be the main board or the T-CON board (this board is mounted on the to center of the screen). The purpose of the backlights is to give the light source for the screen and that is, newer TV uses LEDs for light source instead of CCFL. Please post the pictures of the whole chassis so we can see how all the boards are connected together.
Please read my basic guide in the PDF attached.

Attached Files

Basic LCD TV and Monitor trouble shooting guide by BM.pdf (572.0 KB, 141 views)

**IRShifty** · 03-04-2012, 07:30 PM

Re: LG 42LB1DR No Video or Sound

Originally posted by tom66

3.4V seems to be your problem if it's around 1.5-1.8V. *Especially if it is rising while you take the measurements.*

But... I note this TV has a HDD and that some LG TVs with HDDs have problems powering up with a bad disk drive. (I know, stupid design, given HDDs have a fairly high failure rate.) Try unplugging the HDD power and SATA cable and seeing if it powers up properly.

Can you remove the power supply and take a picture of the underside? I will try and figure out how the 3.4V is generated. On most LG TVs it is generated using a secondary DC-DC converter and it's possible this could go bad (but I've only ever seen bad caps on those types of converters, and only once on an LG LCD.)

I also read that the hard drive can cause issues. With the HDD unplugged it still does not power on properly. I have attached a picture of the underside and a scan of it. The scan is missing a tad on the edges so use the picture to see the edges if needed. Note the notch in the corner of the board where the HDD mounting screw is located for direction.Thank you.

Originally posted by budm

"The back lights come on and stay on but there is no picture on the screen." That is the keyed words, if the backlights come on and stay on but you see no pictures, then the problem can be the main board or the T-CON board (this board is mounted on the to center of the screen). The purpose of the backlights is to give the light source for the screen and that is, newer TV uses LEDs for light source instead of CCFL. Please post the pictures of the whole chassis so we can see how all the boards are connected together.
Please read my basic guide in the PDF attached.

That's exactly what i was thinking and that is why i was surprised when there was so much web chatter about it being bad caps on the PSU. I have attached a picture of the entire chassis. There are 3 additional boards under the chassis which are the CCFL inverter boards and the LCD inverter board. Thank you.

Attached Files

**budm** · 03-04-2012, 07:59 PM

Re: LG 42LB1DR No Video or Sound

See the PDF, the T-CON is under the main chassis and it is also covered by another metal shield, very bad chassis design.
Sine I have never work on one of these TV with Hardrive, not sure if you will see anything on the screen if the drive is bad. Do you see anything using flashlights?

Attached Files

LG 42LB1DR chassis redlined.pdf (413.6 KB, 85 views)

**IRShifty** · 03-04-2012, 09:09 PM

Re: LG 42LB1DR No Video or Sound

Originally posted by budm

See the PDF, the T-CON is under the main chassis and it is also covered by another metal shield, very bad chassis design.
Sine I have never work on one of these TV with Hardrive, not sure if you will see anything on the screen if the drive is bad. Do you see anything using flashlights?

Okay, the T-CON board is what I just replaced then. I ordered one from ebay that was pulled from a known working unit. I do not see anything using a flashlight either but it is hard to tell when I cant tell which input it is trying to read from and I do not know where the normal OSD is because I have never seen this model when it is working.

**tom66** · 03-05-2012, 01:21 AM

Re: LG 42LB1DR No Video or Sound

Check these things in the image. I think the 1.8V output from the 3.4V is -really- unusual.

It looks like the 6V is generated the same way using a buck converter, but that is working, so it gives something to compare against.

Attached Files

**IRShifty** · 03-06-2012, 12:35 AM

Re: LG 42LB1DR No Video or Sound

Originally posted by tom66

Check these things in the image. I think the 1.8V output from the 3.4V is -really- unusual.

It looks like the 6V is generated the same way using a buck converter, but that is working, so it gives something to compare against.

Not sure how i should test those spots on the board. The board is reading 1.9v all over that area but it is not being signaled as on. For the PSU to be hooked up to the main board and get the ON signal it has to be mounted on the chassis so I can not test the under side of the board. How should I test for short circuit? After some fiddling and testing everything is hooked up the same as the last test and all 3.4v except the blue 3.4v which is ON/OFF are now reading 1.25v. Super weird. When the Green connector is removed from the PSU there is almost no voltage on the 3.4v lines. This may mean the 1.8v and 1.25v readings are coming from the main board instead of the PSU.

**IRShifty** · 03-07-2012, 11:59 AM

Re: LG 42LB1DR No Video or Sound

Any ideas on what to check next?

**alikhasan1** · 03-09-2012, 09:58 PM

Re: LG 42LB1DR No Video or Sound

Hello guys,
I have a LG 42LB1DR . I have the problem with the tv having no picture/sound.The result of doing this is that I get nothing. When I plug the tv in, I can hear a click and a sound like something is spinning up. There is a red light on, on the front of the tv. I let it sit like this for a few minutes then hit the power button on the remote. The red light will change from red to a bluish white and flash for a few seconds. Then stay on steady. About this time the screen back light will come on but the screen is otherwise blank.
.So far with mor info its look like some off capacitor on the power supply . I bought so the caps, and replaced c201 c202 c219 and c235. However i still have the same problem.I have just a blue screen with no vedio or audio . is the is another capacitor need to bee chang or any thing ells . need help thanks .
Any help?

**tom66** · 03-10-2012, 03:49 AM

Re: LG 42LB1DR No Video or Sound

Originally posted by IRShifty

Any ideas on what to check next?

Check the inductors I highlighted using your ohmmeter - they should read close to zero ohms.

Check the voltages at those points with the board plugged in and powered up, it may be possible to check from the top side.

**tibimakai** · 03-10-2012, 10:42 AM

Re: LG 42LB1DR No Video or Sound

there is no famous U33 regulator or something similar on this main board which provides the 3.3v?

**IRShifty** · 03-10-2012, 04:05 PM

Re: LG 42LB1DR No Video or Sound

Originally posted by tom66

Check the inductors I highlighted using your ohmmeter - they should read close to zero ohms.

Check the voltages at those points with the board plugged in and powered up, it may be possible to check from the top side.

Both inductors read zero ohms. The only thing in that voltage area on the top side is a capacitor and I can not test the + on the capacitor with it in the circuit. Would it be a sufficient measurement to remove the capacitor and then power the unit on and test the + on the board? Thanks

BTW all 3.4 are back to reading 1.8

**tom66** · 03-10-2012, 06:38 PM

Re: LG 42LB1DR No Video or Sound

Originally posted by IRShifty

Both inductors read zero ohms. The only thing in that voltage area on the top side is a capacitor and I can not test the + on the capacitor with it in the circuit. Would it be a sufficient measurement to remove the capacitor and then power the unit on and test the + on the board? Thanks

BTW all 3.4 are back to reading 1.8

I wouldn't recommend removing the capacitor, as it may have an important function.

I have just noticed there are these copper fins (probably heatsinks) on the top and that they are connected to certain nodes in the circuit. One of them connects to the input voltage to the buck converter for the 3.4V output. It's likely to be this one, but it could be the one to the right of it. Check the voltage on each of these relative to the metal case or a spare screw hole while the TV is on.

Also what is the part # on U214 (the black 8-legged chip.) It's on the bottom of the board (green side) and near those copper heatsinks.

Attached Files

**IRShifty** · 03-10-2012, 07:26 PM

Re: LG 42LB1DR No Video or Sound

Originally posted by tom66

I wouldn't recommend removing the capacitor, as it may have an important function.

I have just noticed there are these copper fins (probably heatsinks) on the top and that they are connected to certain nodes in the circuit. One of them connects to the input voltage to the buck converter for the 3.4V output. It's likely to be this one, but it could be the one to the right of it. Check the voltage on each of these relative to the metal case or a spare screw hole while the TV is on.

Also what is the part # on U214 (the black 8-legged chip.) It's on the bottom of the board (green side) and near those copper heatsinks.

I receive 1.8v on that copper fin and the one above it. The one to the right reads 5v. part# on U214 is 3037CS. Thanks

**tom66** · 03-11-2012, 04:16 AM

Re: LG 42LB1DR No Video or Sound

I expect that the controller itself is faulty then or the MOSFETs are.

Here's a datasheet for the controller. http://pdf1.alldatasheet.com/datashe...IRU3037CS.html

The 1.8V on that fin is unexpected. However, it may be that your multimeter is averaging out the waveform there (which would make sense as that is how a buck converter sort of works.) The intermittent start-up seems familiar as we have seen that before with faulty controller ICs and voltage regulators.

Just for future reference -

I note they are being sold on eBay: http://www.ebay.co.uk/sch/i.html?_fr...All-Categories

but DigiKey has them for $3.75 http://search.digikey.com/us/en/prod...FCT-ND/2441095 +$2.75 shipping

--

How confident do you feel about taking some voltage measurements on U214 while the TV is plugged in? Do you think you could flip the board and make the measurements?

**IRShifty** · 03-11-2012, 11:37 PM

Re: LG 42LB1DR No Video or Sound

Originally posted by tom66

I expect that the controller itself is faulty then or the MOSFETs are.

Here's a datasheet for the controller. http://pdf1.alldatasheet.com/datashe...IRU3037CS.html

The 1.8V on that fin is unexpected. However, it may be that your multimeter is averaging out the waveform there (which would make sense as that is how a buck converter sort of works.) The intermittent start-up seems familiar as we have seen that before with faulty controller ICs and voltage regulators.

Just for future reference -

I note they are being sold on eBay: http://www.ebay.co.uk/sch/i.html?_fr...All-Categories

but DigiKey has them for $3.75 http://search.digikey.com/us/en/prod...FCT-ND/2441095 +$2.75 shipping

--

How confident do you feel about taking some voltage measurements on U214 while the TV is plugged in? Do you think you could flip the board and make the measurements?

Okay thanks for the info. I really appreciate your assistance. Digikey definitely looks like the way to go on the controller. I should be able to take those measurements. Wont be easy but with some special placement I think it is possible. I will take them in 20hours from the time of this post if I have the time.

**tom66** · 03-12-2012, 01:29 AM

Re: LG 42LB1DR No Video or Sound

Just check the voltage on each pin relative to an exposed screw hole.

LG 42LB1DR No Video or Sound

LG 42LB1DR No Video or Sound

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