Burst Capacitor and Vertical Failure In TV After Lightning Strike
This CRT TV was brought to me in dead condition reporting that it became dead after a lightning strike. After going through the routines, which have been explained many times in my earlier articles, I assessed the damages on the board. Found one capacitor 4.7/160V burst and PTC strained, both of which were replaced.
I also replaced the 100/160V and 10/250V capacitors near the FBT and also the 4.7/25V capacitor on the CRT PCB. Retouched all points on the main board where I suspected dry solder. Retouched the entire CRT base Board. When I removed the focus voltage pin from the CRT PCB for lubrication, look at what I chanced to find:
I removed the cut pieces of wire from the CRT Socket (we have to press the holder pin down and remove the strands), and cleaned the portion thoroughly to remove the fungus. Then cut the wire and stripped it to the correct length and applied solder on it for proper bonding. Lubricated all CRT sockets and also the other connectors on the board.
Connected the board and powered on and observed vertical failure. This TV was using IC STV9302A for its vertical output, the pin two of which was the supply voltage. Checked and found that the voltage was present on the pin, indicating failure of this IC.
Disconnected the power, discharged the tank capacitor, looked for any bad components around the IC and replaced the IC from my stock. Powered on the set and found red color spread on the screen. Checked the RGB drive voltages on the CRT PCB and found these to be normal. This can also happen due to failure of PTC, movement of CRT in charged condition and if the set is dropped. One of my friends told me, this can happen due to lightning too.
When I had cleaned the set, I had observed a crack on the bottom of the front side of the cabinet, indicating a fall. Anyhow, I used by External Electric Degaussing instrument and rotated around the four sides of the tube, aiming and keeping it around 10” away from the CRT, quickly bringing the rotation to its inner circles and withdrawing it when it reached the middle portion. I had to repeat it a couple of times to remove the color patch.
You have to connect the degausser to the mains and press the button to activate the electromagnet.
After getting the blue raster, I fed a video signal and found the set to be working perfectly well. It was a lucky set to have survived the lightning strike with very minimum damages.
Here is the set in working condition along with the picture of replaced parts
Thus yet another satisfactory work got collected to my bag!
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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