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Dead Panasonic TC-21FX21C3 CRT CTV Repaired
This CRT TV was brought to me with a complaint that the TV was getting on only after several minutes, then it started making crackling noises, and now it has become dead.
After opening the cover and doing a thorough cleaning inside, discharging the anode, removing the board, and wiping clean the CRT, inside of front and rear cabinets, I brought the TV to my workshop (one of my bedrooms converted as workshop!) I usually keep TVs on the car porch in front of my house and do all cleaning there, so that all the dirt and dust do not get collected inside my house!
On inspection of the board, I noticed that there were several dry solders in the SMPS area, secondary supply area, LOT area, CRT Board and especially on the Microcontroller IC. So, did a cleaning of the board and retouched all these points, which took almost about two hours of sitting. See how the board looks after retouching and cleaning. The second picture is that of the Microcontroller IC. Unfortunately, I forgot to take pictures of the dry solders on this IC, which were very prominent!
Noticed that the anode wire was not in good shape and the anode cap had got hardened and developed cracks. When I tried to move the anode wire out of its cap, the cap cracked like brittle plastic:
Then I cleaned the anode wire and the cap fitting area on the CRT. While doing this, I noticed that the connector at the end is shaking. So, I opened it. See the dry solder in the picture below! The other pictures will show the cap fitting area before and after. The area had undergone a general cleaning before because of which it is in this condition. Otherwise it was very badly darkened. Also look at the anode wire after cleaning.
Then, applied a thin layer of spark guard around the anode cap area on the CRT, and wiped it clean. Cut the anode wire at the end, inserted a heat-shrink-sleeve on the anode wire, and used heat blower of my SMD rework station to fix it firmly, and fit a new cap. The sleeve was used to prevent any leakage from the wire. Leakage to air from this wire due to aging and wearing out is a common cause for loss of high voltage power and arcing.
Then checked the SMPS transformer and LOT (Line Output Transformer or Flyback Transformer – FBT) using the Ring Tester assembled by me long back for this purpose:
Found both in perfectly OK condition. Used ESR Meter and checked capacitors in SMPS as well as secondary power supply, CRT Board, and around FBT area, and other capacitors at random. Did not find anything wrong and not even a single component needed a replacement, in spite of 9 years of life of this TV! I also noticed that this is the first time; the back cover was being opened!
So, removed the jumper wire that goes to the primary winding of the FBT, connected a 100W bulb and checked. The Bulb lit and the voltage read was 140 V, which is correct for this CRT TV. So, I knew that there is nothing wrong with the power supply. Replaced the jumper wire and connected the board back to the CRT, rechecked all connections, especially the earth wire to the CRT board (If we do not provide a good ground to the backside of the CRT, when high voltage is generated in the anode, it is likely to damage the CRT and other components in the FBT area!) Connected the TV to mains and switched on. It came on without any problem and the raster was also good. So, connected a video input and checked. The Picture was good. Ran the TV for several hours. Put back the cover, as the TV was stable. See the quality of pictures in spite of the age of the CRT TV:
The pictures are taken from a running VIDEO, and might, therefore look hazy. So, another job done satisfactorily.
This article was prepared for you by Parasuraman Subramanian from India. He is 66 years old and has more than 30 years’ experience in handling antiques equipment Valve Radio, Amps, Reel Tape Recorders and currently studying latest techs classes conduct by Kerala State Electronics Technicians’ Association. He was a BBA graduate, retired as MD of a USA company.
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