Leaky Capacitor Caused Onida CRT TV To Become Dead
MAKE AND MODEL: ONIDA CO21SJG350BR CRT TV
COMPLAINT REPORTED: Dead
TROUBLESHOOTING AND RECTIFICATION DONE: Opened and cleaned the set thoroughly. Discharged the anode, disconnected the yoke, CRT Earth Wire, Speakers and Degaussing Coil. Removed the CRT Board from the neck of the CRT by slightly shaking and slowly pulling it out without causing strain to the pins or neck. Some CRT PCBs, if not opened before, might be stuck with some glue to the neck. We have to carefully see and then remove. Otherwise we are likely to damage the CRT neck, especially if we use force. Cleaned the board also thoroughly and brought it to work table for visual examination. Found a lot of dry solders. ESR of caps were out of range in most. Ring testing on the SMPS transformer and FBT (LOT) was ok. Could not find any burnt fuse or other components in the SMPS primary. Disconnected the jumper wire that goes to primary of the FBT to the collector of Horizontal Output Transistor.
Then connected a 100W bulb and powered on the set. Found B+ missing. So, the SMPS was not switching on. Disconnected the power and checked for 300V DC in the tank capacitor. Did not find it. Either there is a quick discharge or the cap itself is bad. The ESR of this cap was already tested to be very poor. So removed it and was not surprised to see that it had leaked underneath though we cannot see anything from the top. So, to begin with, I replaced all the electrolytic capacitors in the power supply section including the B+ 110V line. Then applied power and found that the 110V DV was perfect and the loaded bulb lit indicating that the power supply section was ok. Then reconnected the jumper wire, and connected it to CRT, by putting back all the connectors, before which I applied drop of lubricant cleaning oil in every sockets of connectors, including the CRT Socket. Found that the raster was ok. The picture was not good enough when connected to a Video input. So, once again removed the board after discharging anode and replaced all the electrolytic capacitors on the board and did a thorough dry solder patch up from one end to the other. Cleaned the board thoroughly and allowed it to dry up before connecting it back to the CRT. When the set was powered up, it was found working very well. After allowing it to run for several hours, informed the customer to come and pick it up. Mission accomplished and satisfaction got added!
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This article was prepared for you by Parasuraman Subramanian from India. He is 70 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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