LG 50PC3D-UD power issue

[nswizdum]

I recently picked up a LG 50PC3D-UD to repair. When I power the TV on, I hear the relays click, the green led on the front blinks 3 times and then goes back to red. I tried searching around a bit and found that these units have issues with the 10v 3300uf caps on the power board. All the caps look fine to me, no obvious bulging or leaking, but I replaced them anyway. The TV still wont power on fully. I found some LEDs that look like they may be error codes, and I included a picture of them. I also noticed a green and red LED under the shield on the tuner. I also tested all the pins on the p801,802, and 803 connectors. All the voltages were fine, except for the 3.3v pins, there was never any power on those pins.

Not sure if its a problem or not, but the two green thermistors next to the 2 black relays on the power board are closed at room temperature. This means that they are shorting the two load pins on one of the relays which seems like odd behavior to me, but it may serve a purpose I am not aware of.

I found what appears to be a service manual, but I am not sure how to follow it to diagnose these problems.
http://www.scribd.com/doc/7580885/LG...raining-Manual

Has anyone here worked on these sets before? I'm new to the world of plasmas and I don't really know where to proceed from here.

The pictures are too big to upload here, so I put them on google Picasa:
http://picasaweb.google.com/joshuabu...eat=directlink

Thanks in advance,

[PlainBill]

Re: LG 50PC3D-UD power issue

The 3300uF, 10V cap problem is for Philips plasmas and otehrs using a Samsung panel. LG electronics makes their own panels, so that bit of wisdom doesn't apply here.

I'm drawing a blank on a service manual for this TV. Perhaps you can find a cross reference here.

Either use software to reduce the size of the pictures or reduce the resolution of your camera. Remember, use 'Manage Attachments (below the text entry area), do not post pictures inline.

Because of past problems, I refuse to load pictures stored offsite.

On the back of the plasma panel there should be a white label that starts with PDP50. What is the full model number of that panel.

PlainBill

[cadiman]

Re: LG 50PC3D-UD power issue

It looks like these use ipms. You may have a bad y drive board and that would shut down the power supply. I am not sure about about this model but most of the one`s I have worked on you can unplug the y or z board and power up the tv and see if the power supply stays up and runs. Try and search old posts you might find the info you are looking for.

[nswizdum]

Re: LG 50PC3D-UD power issue

Thanks for the replies. I understand the problem with off-site pictures, I figured Google would be fairly trustworthy. I'll try to find a way to shrink them down.

I did hear about unplugging the y or z board, and I just tried it after posting this. I still had the same problem when unplugging all 3 cables, and when unplugging each one separately.

The full model number is PDP50X30010.DDDRBAB

I will edit this post and add in the attached pictures (if that is permitted on this forum) or I will post them in a few minutes.

[nswizdum]

Re: LG 50PC3D-UD power issue

Here's the pictures. I included some of the surrounding boards too. Where do I find the Chassis number on the panel? I get no service manuals for PDP50X30010.

[PlainBill]

Re: LG 50PC3D-UD power issue

Here's the pictures. I included some of the surrounding boards too. Where do I find the Chassis number on the panel? I get no service manuals for PDP50X30010.

I envy you. The LG 50PC3D chassis uses the same panel as the LG 50PC1D chassis. I believe this file was obtained from Scribd; Elektrotanya's server is down this morning.

What you want is 16077007-LG-50PC1DRTroubleshootingManual-2007-VG-Training.pdf

This manual goes into exquisite detail on troubleshooting the entire chassis, including the panel, power supply, sustain and main control cards. It also contains information on the hard drive.

Incidentally, I prefer to see an over-all shot of the back of the TV as one of the pictures. That puts the rest of them in perspective.

PlainBill

[nswizdum]

Re: LG 50PC3D-UD power issue

That service manual looks like its going to be immensely useful, although my TV doesn't have a hard drive in it.

Here's a shot of the back panel.

[nswizdum]

Re: LG 50PC3D-UD power issue

Ok, I just double checked all the pins for the 800,802, and 803 connectors. All the voltages except 3.3v are still fine, and I do have 5v standby when the tv is plugged in. I'm going to wait for any residual charge to dissipate then check the mosfets in the "HS6" section of the power supply board.

[PlainBill]

Re: LG 50PC3D-UD power issue

Ok, I just double checked all the pins for the 800,802, and 803 connectors. All the voltages except 3.3v are still fine, and I do have 5v standby when the tv is plugged in. I'm going to wait for any residual charge to dissipate then check the mosfets in the "HS6" section of the power supply board.

Yah, no 3.3V would cause problems.

PlainBill

[nswizdum]

Re: LG 50PC3D-UD power issue

Scratch that, I can measure 3.3v when all cables are plugged in, it must come from one of the attached boards. Any ideas on where to proceed from here?

I should also specify that when I said all the voltages on the pins were good, I was only referring to the ones that were labled. The VS-ON pin never shows a voltage.

[nswizdum]

Re: LG 50PC3D-UD power issue

Scratch that, I can measure 3.3v when all cables are plugged in, it must come from one of the attached boards. Any ideas on where to proceed from here?

I should also specify that when I said all the voltages on the pins were good, I was only referring to the ones that were labled. The VS-ON pin never shows a voltage.

Looking at the service manual, I realized that VS-ON comes from the digital board, so it would read 0v with the cable disconnected. I re-attached all the cables and tested the VA and VS pins (I am going through the "power sequence" listed in the manual to try to find where it is stopping, since I can hear the relays click, and can read 3.3V, 5V, 6V, 12V, and 19V, I know it is making it to step 3). I read 0v on VS, and VA gets to 5v before the tv turns off.

[PlainBill]

Re: LG 50PC3D-UD power issue

Looking at the service manual, I realized that VS-ON comes from the digital board, so it would read 0v with the cable disconnected. I re-attached all the cables and tested the VA and VS pins (I am going through the "power sequence" listed in the manual to try to find where it is stopping, since I can hear the relays click, and can read 3.3V, 5V, 6V, 12V, and 19V, I know it is making it to step 3). I read 0v on VS, and VA gets to 5v before the tv turns off.

That goes back to cadiman's comments. On some LG plasma TVs you can troubleshooting by disconnecting Y and Z sustain boards. On others you will still get a failure when you disconnect the Y-Sustain board - it detects the disconnected cable as an error.

As I recall, the training manual has information on troubleshooting the IPMs.

PlainBill

[nswizdum]

Re: LG 50PC3D-UD power issue

The VS and VA voltages are generated on the power board though, correct? So wouldn't the problem still be located there, and not in the IPM module? Or could the IPM module be causing the failure once it starts receiving power from the VA source(the 5v it gets up to before the tv shuts back off)?

[PlainBill]

Re: LG 50PC3D-UD power issue

The VS and VA voltages are generated on the power board though, correct? So wouldn't the problem still be located there, and not in the IPM module? Or could the IPM module be causing the failure once it starts receiving power from the VA source(the 5v it gets up to before the tv shuts back off)?

Correct. The blown IPM overloads the power supply, which shuts down to protect itself.

PlainBill

[nswizdum]

Re: LG 50PC3D-UD power issue

I pulled the YSUS board and tested the IPMs as it was described in the manual, I think. I put my meter in diode test mode and tested all the pins in the order listed, there was a decent amount of resistance between all of them, no open or shorted circuits. I also checked over the caps and mosfets for any obvious signs, didn't find anything. I'm going to look around a bit more then move on to the ZSUS board.

[nswizdum]

Re: LG 50PC3D-UD power issue

Also, page 59 of the troubleshooting manual states that when the YSUS board is disconnected from the power board, there will be "no display". Would that mean that the power supply should still function with that cable disconnected?

Sorry for the multiple posts, I keep missing the window for editing.

[PlainBill]

Re: LG 50PC3D-UD power issue

Also, page 59 of the troubleshooting manual states that when the YSUS board is disconnected from the power board, there will be "no display". Would that mean that the power supply should still function with that cable disconnected?

Sorry for the multiple posts, I keep missing the window for editing.

Yes, it does. The training manual for an earlier series of LG Plasma TVs was very clear that testing the Y-Sus by disconnecting the power cable from the Y-sus was not possible. This would be treated as a failure and cause the power supply to shut down. This sounds like they have updated the design.

PlainBill

[nswizdum]

Re: LG 50PC3D-UD power issue

Yes, it does. The training manual for an earlier series of LG Plasma TVs was very clear that testing the Y-Sus by disconnecting the power cable from the Y-sus was not possible. This would be treated as a failure and cause the power supply to shut down. This sounds like they have updated the design.

PlainBill

So now the question is, which design do I have? This is getting interesting.

[PlainBill]

Re: LG 50PC3D-UD power issue

So now the question is, which design do I have? This is getting interesting.

Well, given that your training manual DOES mention disconnecting the power to the Y-sus, I'd believe the tests indicate your problem is not with the Y-sustain. Other than the exception mentioned above, the power supply outputs should be good if all sustain boards are disconnected.

PlainBill

[nswizdum]

Re: LG 50PC3D-UD power issue

I took another look at the power board and found a component that may be the problem. It looks like a large voltage regulator or mosfet, it's labeled Q855 on the schematic (it connects directly to the transformer that generates the VS voltage). It shows less than 15ohms resistance between each pin, in both directions, which is different from the other similarly labeled components. Theres also a box capacitor next to it that is caved in on the sides.

The part is labeled "SD20N60" and "GAV602" on the front. I'm going to head over to my local parts supplier tomorrow and see if he can find a replacement. The store sells mostly NTE parts, for future reference, are NTE caps generally of good quality?