LG 42PJ550 42" Plasma TV - Page 1
Forum section: electronics / repair

author: Mad Professor
author_rank: Regular Contributor
timestamp: January 12, 2018, 07:38:27 pm
content: Hi All.I am hoping for some help and advice with regarding to repairing a LG 42PJ550 42" Plasma TV.When the mains power is turned on the TV just clicks it's relays on and off repeatedly, and will not switch on.I have been trying to find a suitable Schematic for the main power board but I am having no luck, below are the PCB details.PCB: EAX61415301/8PSU P/N: EAY60912401Rev 1.32010So far I have tested that all the fuses and power resistors are good.I have read that is the LG Plasma TV's that is quite conman for the Regulator/Controller and input Diode to fail.In my case that would be a 3BR1565JF and SR104 Diode. I have replaced them as coarse.The TV will not switch on straight away, but if you leave the mains on the relays will continue to click after some time the pattern of clicking will change, then the TV can be switched on.The TV will work as normal for up to 10 minutes then it will turn off again and start clicking.To me this is sounding very much like a failed capacitor. but I would really like to know your thoughts.If anyone could point me in the right direction to a suitable Schematic for the TV or just the power board I would be most grateful.Thanks for your time.Best Regards.

author: james_s
author_rank: Super Contributor
timestamp: January 12, 2018, 09:40:37 pm
content: The first thing I do when working on something with this sort of symptom is check the voltages out of the power supply, then check all of the electrolytic capacitors in the power supply.

author: Mad Professor
author_rank: Regular Contributor
timestamp: January 13, 2018, 08:04:58 pm
content: james_s: Thank you for your reply.I only seem to be getting the 5v standby voltage out of the psu.I have limited testing abilities, but have removed all of the electrolytic capacitors and tested them with my DMM but that can only test up to 100uF, unfortunately I don't own or have access to a ESR or LCR meter.all the caps up to 100uF are within 5%.Do you happen to know if it is possible to find a Schematic for the TV or PSU?Thanks for your time.

author: Armadillo
author_rank: Super Contributor
timestamp: January 13, 2018, 09:18:17 pm
content: http://tomtechtodrepair.blogspot.sg/2015/04/a-reverse-engineered-schematic-and-diy.html

author: james_s
author_rank: Super Contributor
timestamp: January 16, 2018, 08:52:10 pm
content: A DMM is nearly useless for testing capacitors, you need an ESR meter, or just replace any that are at all suspect.

author: Mad Professor
author_rank: Regular Contributor
timestamp: January 20, 2018, 06:50:07 pm
content: Thanks for your replies.Armadillo: Thank you for the link, It's a different board to this one, But it sure will give me a good place to start.I will have a good read over it tomorrow.I would ideally like to fault find the issue instead of just randomly replacing components.As I would not of learnt anything.Here are a few pictures of the board:Here is a list of the main capacitors on this board:As said before sometimes the TV will power on fully and work, So I have been trying to test voltages between working and not working.Also as said before the main relays are clicking on and off repeatedly.After removing the covers I noted that the 2nd relay (RL101) was clicking on before the 1st relay (RL103).I would of thought that the 1st relay (RL103) in line would come on before the 2nd relay (RL101).But from reading the link that Armadillo kindly provided this seems to be normal.Thanks again for your time.

author: zvonex66x
author_rank: Contributor
timestamp: January 20, 2018, 10:48:20 pm
content: In the horizontal board you have IGBT Rjp6065, test it, i'm sure that they are short

author: zvonex66x
author_rank: Contributor
timestamp: January 20, 2018, 10:53:29 pm
content: Do you try disconnect the left(z-sus) board from power supply. If not, try and then see if will be clicking sound?

author: dave_k
author_rank: Frequent Contributor
timestamp: January 20, 2018, 10:59:07 pm
content: If the TV sometimes powers on and works, you might be wasting time testing for failed parts. If some transistor or MOSFET was shorted, then it would not work at all.Under what conditions does the TV begin to work, or not work? Try to learn from these observations. Chances are you're probably looking for a intermittent or "dry" solder joint somewhere. While the TV is in it's "clicking on and off" state, try gently prodding various parts and connectors with a insulated stick.

author: zvonex66x
author_rank: Contributor
timestamp: January 20, 2018, 11:11:05 pm
content: I know why i have say that he need to test IGBT in z-sus board.. working with tv repair 10years.. in this plazma tv you have 3 line of IGBT connected in parallel driven by IC and when one of this IGBT get shorted, the ic will sometimes turn others two line of IGBT and left turned off one shorted, but then after 10-15minutes those two line become overheated and tv go off again.

author: Armadillo
author_rank: Super Contributor
timestamp: January 21, 2018, 06:55:26 am
content: It all begins here.Have you downloaded the schematic from the site?Measure the voltage of the IC pins, the caps etc per attached.Everything begins there.Please wear protective gear, that section is LIVE "HOT" and dangerous.At least even a "DRY" dishwasher glove if you really must do it.****MEASURE OHMS ONLY WHEN POWER UNPLUGGED AND CAPACITORS DISCHARGED*********MEASURE OHMS ONLY WHEN POWER UNPLUGGED AND CAPACITORS DISCHARGED*****

author: james_s
author_rank: Super Contributor
timestamp: January 21, 2018, 09:21:37 pm
content: If you want to diagnose and repair something without just replacing parts based on educated guesses you'll need to have the right tools. In this case an ESR meter is one of those tools. A can of freeze spray (or air duster held upside down) is helpful for thermally sensitive faults.

author: nimor
author_rank: Newbie
timestamp: December 22, 2020, 07:45:10 am
content: I want to ask the owner if he has rectified the defect. I have the same problem with the LG 42pj550. The relay keeps clicking repeatedly.