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Flyback Arcing And Burnt CRT Base PCB Found In 14″ CRT TV
This 14” CRT TV Model No.CTVTN14 was brought to me with the complaint that the customer heard fire works inside the TV when he switched it on, after keeping it idle for a long time. Immediately he switched it off and brought it to me along with another 21” CRT TV, which was also lying in his house, after noticing smoke coming out on switch on. He was not using both these TVS for quite sometime now, as he had bought an LED TV. But that went dead due to lightning and that’s how he happened to switch the 14” CRT TV on. Looked like, it was bad day or time for him and his family (but good time for me!!!).
Now, please do not ask me the brand, as it was given by the Tamil Nadu Government as gift and it does not have any name written on the rear label or front panel. It used a Philips uController. The remote number seems to be that of LG.
As usual, the first duty was thorough cleaning inside and outside, which I did. The TV was having full of dust, dirt and filth inside it. It took almost 30 to 40 minutes for me to do the cleaning. I had disconnected the Main PCB, after discharging the anode for any residual stored high voltage, in the process of my step by step cleaning.
On inspection of the PCB, I noticed a lot of dry solders, the CRT Base PCB was found darkened due to overheating and one Fixed Capacitor was found broken near the LOT (Line Output Transformer – Flyback Transformer – FBT). All was not well with the Board and I started my rectification work one by one. First I checked for any burst capacitors, or strained components and then checked the ESR of a few capacitors in the power supply as well as in the horizontal and vertical sweep sections. Could not find any in the main board, but the CRT PCB was in bad shape as mentioned earlier. After finishing retouching of the entire main board with fresh solder, I removed the transistors from the CRT PCB,
primarily for cleaning up the darkened PCB and checked it up. Found a couple of transistors defective. Replaced these after thorough cleaning of the CRT PCB. Now let’s look at the pictures:
Connected the board, after replacement of the burst capacitors near the LOT, and reworking on the CRT PCB. Saw arcing taking place at the base of the LOT to the nearest ground point, indicating that the LOT was defective. Disconnected, and discharged the anode, and removed the LOT and fetched a replacement and fixed it. Reloaded the PCB and switched on, after keeping the focus and screen controls to the minimum. When the CRT filament was on, slowly turned the screen control for a very light blue background. Since the remote control was not working and its inner linings were found badly.
damaged, I had obtained a replacement. Adjusted the contrast, brightness, sharpness and color to the minimum and ensured the screen was just dark, by adjusting the screen control. Then increased the Brightness and contrast to the required level. Fed a video signal, and adjusted these to the required level. Also adjusted the focus and then used the menu to adjust the sharpness to the required level. Thus picture alignment was completed. Now let us see the pictures:
This is the finished TV with its remote waiting for pick up by customer.
You can see also the parts replaced:
Thus another interesting and rewarding work completed to my utmost satisfaction, allowing the bag to bulge further!
This article was prepared for you by Parasuraman Subramanian from India. He is 69 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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