Where To Check For A Very Bright Display Fault In CRT Monitor/TV
This kind of problem of bright display with flyback lines across screen one has to concentrate on the G2 (screen voltage) and G1 voltage. The G2 voltage has to be within range (typically 250 to 300vdc) and if it set to too high the above symptom will appear.
As for G1 voltage, it should be negative voltage and if you get zero voltage then you can expect the same problem.
In certain designs, a missing dc supply voltage (usually 12 volt) to the video pre amplifier IC also could cause such problem. In rare cases a shorted cathode and the G1 electrode in the picture tube also would cause similar fault. I also have seen a faulty vertical output IC that had caused the above problem.
So there you are, few possibilities of circuits to suspect. Check the circuit one by one and I’m sure you will find where the faulty section/component is.
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Zed
October 5, 2013 at 12:19 pm
great tips sir. thank you.
Zed
Jestine Yong
October 5, 2013 at 8:24 pm
HI Zed,
You are welcome!
Jestine
Waleed Rishmawi
October 5, 2013 at 8:38 pm
i had almost the same problem with a JVC tv set. I could see these lines on the screen but also you can see the actual picture. when hitting the tv on the side, the tv comes back normal for a few minutes then the probem startes again. it has to do with cold soldering joints on the ocilator Ic. resolder all the pins of the ic, fixed the problem.
Jestine Yong
October 5, 2013 at 8:54 pm
HI Waleed,
Thanks for the comment!
Jestine
KIM
July 14, 2024 at 3:42 pm
hello,sir Waleed.
I have LG slim TV(21fu1r-ns of 220 voltage) and It has also the same problem(lines across screen) whenever the screen is completely black.
But It also possible to see the actual picture.
I adjust screen potentiometer on the flyback transformer,But It was impossible to get rid of these lines across screen problem.
The below links is a schematic of MC059C PCB,and It seems that most of crucial components is the same to 21fu1r-ns.
https://i.imgur.com/kkLKfZN.jpeg
Following your tutorial,I want to resolder all pin of ocilator Ic in order to solve this problem(lines across screen),But I cannot locate a component, which is ocilator IC, from MC059C schematic.
I really appreciated if you would let me know which components is real ocilator IC from MC059C schematic.
VenuGopal
October 6, 2013 at 1:51 am
I faced the same issue several times before,generally this is because of bad capacitor (10mf/250v or similar) in the 200 voltage supply line,which gives power for R,G,B output transistors.
Jestine Yong
October 6, 2013 at 8:14 am
Hi VenuGopal,
Thanks for the tip!
Jestine
raymundo saura
October 6, 2013 at 9:42 am
thanks for this kind of articles very informative and it will help me a lot on my coming repairs thanks and GOD bless
Robert
October 9, 2013 at 1:55 am
Thanks for the article, Mr. Yong. I don't anticipate working on a CRT TV, but I still find it fascinating and I enjoy learning about them.
I received my camera yesterday and I'm learning how to use it. I have to learn how to write an article and how to put in the pictures. Is there a good e-book I can buy that teaches how to do that??
Jestine Yong
October 9, 2013 at 10:57 am
Hi Robert,
You are welcome. As for putting the photos into the article.It is simple to do it. Once you have taken the photo then download it to your computer. Open up your free microsoft paint and select the photo you want to edit. resize the photo with the function found in the Paint and save it under jpeg file. Now open up your WORD and choose "insert" on top of the page. select the photo you have resized and you are done. Hope this helps.
Jestine
Robert
October 9, 2013 at 11:52 am
Hello Mr. Yong. I wrote the article and added some pictures and sent the email but I'm not sure it went through. One of them said your name was not recognized or something like that. If it didn't go through I'll have to find out what is going wrong.
Jestine Yong
October 9, 2013 at 12:40 pm
HI Robert,
My email is jestineyong@electronicrepairguide.com. You can try resend.
Jetsine
Robert
October 10, 2013 at 3:28 am
Yeah!!!! I think it went through!! 🙂
Amir Mukhtar
November 10, 2013 at 4:39 am
Thanks you Sir
yours Student
Amir Mukhtar
semmie
March 23, 2014 at 11:53 pm
Mr jestine thak you for everythngmi was repear telefunken wat happend is tht I found low voltage in dc emetetly I reliese tht my power supply not active yet so I chngd power regulator then power up again. Thanks a lot urs student semmie
habtamu
September 17, 2017 at 5:39 pm
I have sony crt tv with dim display problem. How i can solve the problem?
Jestine Yong
September 21, 2017 at 11:10 am
Hi Habtamu,
Dim display can be caused by weak picture tube, low g2 voltage and even low heater voltage.
Jestine
Kim
July 13, 2024 at 4:01 pm
Hello Jestine Yong,
I have LG slim CRT TV(21fu1r-ns of 220 voltage) which was not able to display any screen.So I did IN CIRCUIT Testing all of capacitor with MESR-100 ESR meter. I found a capacitor which has no ESR and capacitance value at all, It was connected to horizontal coil(C420 250v 1uf). So I replaced this capacitor and other capacitor which is located in the vicinty of FBT(C540 250v 4.7uf) and in the vicinty of Vertical Deflection Booster(STV9326)(C307 35V 100uf) which has somewhat higher ESR value,So I also replaced these capacitor,too.
Below picture is MC059C schematic. It seems that most crucial components is the same with 21fu1r-ns PCB which I try to repiar.
https://i.redd.it/m0b68t9i9drc1.jpg
After replacing three capacitor,It finally succeeded to display a screen,But,the screen was very bright and It displayed lines across the screen like your article. Worst of all, IT IS NOT ABLE TO CONTROL BRIGHTNESS with screen adjust potentiometer on the lower FBT...
Besides I heard a weird static sound near CRT anode cap whenever I turn off this 21fu1r-ns CRT TV like below video.(You can hear static sound from 00:52 to 01:05)
https://www.dropbox.com/scl/fi/36xkcljhnoyw9ffnj8ow1/20240531_150631.mp4?rlkey=e7a51f4ak7p2m9gvuikgfjcx2&st=8ttjyzxy&dl=0
I really want to control brightness with screen adjust potentiometer on the lower FBT and get rid of weird static sound.
I really very much appreciate you if there is workaround to repair this problem and if there is any tutorial to measure G1 voltage.
Jestine Yong
August 6, 2024 at 5:30 pm
Hi Kim,
The sound could be come from the internal sparking of the flyback transformer. As for the brightness control, tracing bad components along the brightness control line may be able to locate the fault. It can be an open resistors, circuit track broken and etc. Without hands on assessment on this TV, it would be difficult for me to tell what is the exact problem.
Jestine