LG 50PQ30C-UA No picture - blank PDP

[tom66]

Re: LG 50PQ30C-UA No picture - blank PDP

In standby, you should have 320~340V in 240V countries; 160~170V in 120V countries.

[damiane]

Re: LG 50PQ30C-UA No picture - blank PDP

Seems like ai had attachnment issue also...let's try again in .pdf.

[damiane]

Re: LG 50PQ30C-UA No picture - blank PDP

Been away for a while, but wanted to thank everyone again for their input. After all the troubleshooting and data gathering, I went ahead and ordered replacement buffer (y-drive) boards that should be delivered today. I will perform tests on the new board before installing to compare the results to the existing. This will mean new buffers and Y-SUS so I am keeping my fingures crossed. Will let you know the results.

[damiane]

Re: LG 50PQ30C-UA No picture - blank PDP

RESOLUTION:
I received the new buffers in and installed them with the same results. After SMH for a while I finally called up the folks at tvrepairguy.com where I got the parts from. They were gracious enought and offered to test all my boards, so yes I cheated a bit. I sent them all the boards from my set (except the PS board) and they would install them in the same tv that was on their test stand.
What the found was that the control board worked, main board worked, Z-SUS worked. New buffers worked, but old buffers and both Y-SUS were bad. with the combination, and a NEW Y-SUS they got the tv working perfectly. So what happened in the first place?
We deduced that the buffers went bad and took out the Y-SUS. I diagnosed the Y-SUS to be bad and replaced it, but as the buffers were bad, they took out the new Y-SUS. After replacing the buffers, tv still didnt work because I had 2 bad Y-SUS. There were quite a bit of input from users which were well appreciated. There was one post that stated that they rearly saw buffer failures on the LG...but this was the exception. As a newbie, this being the first tv I ever tried to repair, I think the main lesson I learned is that buffers and Y-SUS should be changed together unless you can without a boubt pin point which is bad...and from what I saw, the tests for the buffers aren't that conclusive.

Thanks All

[pk7tanner]

Re: LG 50PQ30C-UA No picture - blank PDP

HA! I can't believe I was right. LOL Beginners luck

[Bradb2014]

Re: LG 50PQ30C-UA No picture - blank PDP

So I too am going to attempt to replace the boards this gentlemen replaced because my 4 year old lq 50pq30-ua is occassionally losing picture in every input but still has sound. Also occasionally the picture goes to a rainbow effect. I've talked with a tv repair tech intown about it and he seems to think the ysus board however after reading this i'd like to go ahead and give it a "tune" up on the buffer boards. My ? is does the OP have the part numbers for the buffer boards and were there only 2 to replace? Also should i go ahead and purchase any other boards to replace as I do not want to have to do this very often. I've taken the back off and seen numerous smaller boards attached around the edges. How many buffer boards, any other boards, and part numbers would be much obliged.

[tom66]

Re: LG 50PQ30C-UA No picture - blank PDP

An intermittent issue like that is unlikely to be a buffer board issue. Whilst not impossible, it is more likely that it is a main board or control board issue. You can try using a hot air gun / hairdryer to heat up stuff and try and locate intermittent issues.

[Bradb2014]

Re: LG 50PQ30C-UA No picture - blank PDP

well i've did a little searching for this hot air gun technique as i have just purchased a handy hot air gun at a great price to repair my xbox 360...though im not finding any procedures on this. Could you elaborate? Just blow hot air on different boards and see if picture comes back? is there a certain temp it must reach? Thanks for your help tom66, also though i mean this guy had the same problem...sound but no picture and it was determined the buffers/ysus boards were bad, wouldnt it make sense to start with those to fix the issue? Money really isnt a factor because i can pick up both upper/lower drive boards as well as all three buffer boards and ysus board off ebay for around $150 shipped.

[damiane]

Re: LG 50PQ30C-UA No picture - blank PDP

Can you elaborate a bit more on the intermittent failure? Does the picture go away after watching for a certain period? Does it come back after a certain time? Do you have to cycle power or let tv sit for pic to return? Is it repeatitive? Also, when you say you still have audio, do you actually have audio of the program that was on, or just sound (frying) coming from the speakers? The issue you are experiencing is very different from what I had. I went to turn the tv on one day and there was no pic, and I did not have failures prior. So as Tom66 said, it may not or may not be buffer/y-sus. The reason we normally undertake these projects is for personal knowledge or for financial preservation, and you would like to get as close to the potential cause as possible in order to satisfy either motive. Throwing boards at the tv at this point without due diligence of more detailed troubleshooting doesn't seem to be the appropriate thing. Not saying this won't fix the problem, but there is still a big gap in the data gathering process that I would recommend addressing. There are certain drive voltages on these boards you would want to check. For example if you think it's a Y-SUS issue, verify Vs, Vsc and -Vy to determinre if they are in range. A slight tweak of the Potentiometers to adjust the voltage level could yield favorable results...and if not you can at least start to eliminate components.

But to attempt to answer your main question; if you are set on a Y-SUS replacement, the recommendation is to replace the Y-SUS along with the buffers. There is an additional $80 or so associated with this, but that's what I found to be appropriate and was also recommended by other posts and tv repair shop. The part #s are listed on the board, and there are only two, upper and lower connected by a series of ribbon cables to the left of the Y-SUS. Again, your problem is a bit different and if you are looking for the cost effective solution, I recommend additional analysis of the failure. I have attached some troubleshooting material that may come in handy if you don't already have.

[Bradb2014]

Re: LG 50PQ30C-UA No picture - blank PDP

Well the problem is off and on with the rainbow effect on the screen, has never really lasted very long. The sound but no picture problem just started literally a few days ago, it is also reoccurring, and happening more and more often now...it has been fixing itself just by sitting there on with no picture for a while...i'll attempt to check the voltages if that is the best way.

[tom66]

Re: LG 50PQ30C-UA No picture - blank PDP

Can we see a picture of the fault?

Basically you want to set your hot air gun to 60~100°C and start heating up stuff -- but you're actually looking for the problem to occur so you can locate the fault, instead of trying to cure it.

[Bradb2014]

Re: LG 50PQ30C-UA No picture - blank PDP

alright well i'll try reading some volts and applying mid heat to some boards to see if the problem occurs and get back to you, i have a day off tomorrow so it'll probably be a day or 2 before I can get some results, but i'll let you know. Again, thx!

[Bradb2014]

Re: LG 50PQ30C-UA No picture - blank PDP

Well actually guys, this is going into the 3rd day and its not done it since my last post...obviously something is starting to go wrong or it wouldnt of started, but I wont be taking this tv apart and tinkering with it until i see the problem happening more frequently. I'll be back when the time comes, thanks for the info on the thread though.

[pposey]

Re: LG 50PQ30C-UA No picture - blank PDP

Im having a similar problem with a LG 50pq30. When i power up the tv with every connector plugged in where it goes, the power light on the bottom of the tv will turn blue then red. But if i unplug the y-sus from the power supply i get audio but still not video and the power light turns blue. Also on a side note, the led on the control board is not on.

Do you think the control board is bad and not the y sus or both?

[damiane]

Re: LG 50PQ30C-UA No picture - blank PDP

PPosey, Sounds like a similar issue, except for on mine the green LED on the control board was flashing indicating it was working. In my case the Y-SUS and Upper and Lower driver board being replaced solved my issue. Have you taken any voltage readings. Record Vsc, Vy and Va...and I guess Vzb while you are at it, with and w/o the Y-SUS connected and see what's in and out of range. Then we can go from there. Use the attached file to help you with your troubleshooting.

[pposey]

Re: LG 50PQ30C-UA No picture - blank PDP

Thank you for the reply. I tested with both sustain boards plugged in and the readings were way low. That is when my tv will not no audio nor video. The VA reading was almost 3v and the VS was 46v. But with just one sustain board plugged in , the audio works and the voltages are where they need to be but no video.

[pposey]

Re: LG 50PQ30C-UA No picture - blank PDP

Also i have a audio source connected to hdmi, i will click the input button but im guessing it stays on the same input because they sound never changes. Im still wondering why my control board led is not working and the audio only works if one one of the 2 sustain boards are connected to power supply.

Does anybody know the size of these fuses? its 4.0a 250v but i really dont know the mm size on them

[tom66]

Re: LG 50PQ30C-UA No picture - blank PDP

Fuses are typically 5x20mm.
Really strange, so set will run with Z-SUS or Y-SUS but not both?

[pposey]

Re: LG 50PQ30C-UA No picture - blank PDP

Fuses are typically 5x20mm.
Really strange, so set will run with Z-SUS or Y-SUS but not both?

Yes that is correct. Main board doesnt even seem to work when both are plugged in.

[pposey]

Re: LG 50PQ30C-UA No picture - blank PDP

Ok i found the problem with only one working at a time. The fuse was blown on the y sustain. Now i can plug both of them in with sound but still no picture. It just really bothers me that my led is not working on the control board. Do you think it is done?