Burst FBT Found In 21” CRT TV With China Kit
This TV was brought to me with the complaint that smoke came out when switched on. Though the label shows Sharp 21TK21, it contained China kit, which was fit in a very crude way. The front panel was stuck with tape and was found hanging loose. The input board at the rear was fixed awkwardly, with only one screw. As usual the primary responsibility is to clean the inside of the TV. Just have a look at the inside of this TV, which not only had cob webs, dirt and filth, but also rat excretions!
Now look at the inside after cleaning:
The next job was visual inspection of the Board, which brought out defects such as burst capacitor, burnt resistors and dry solders:
As you will notice, the ABL circuit is the one that had got affected, indicating defects in FBT.
So, I removed the FBT and look at what I found:
The PCB was found charred under the burnt resistors and jumpers under the LOT were also badly damaged, probably due to arcing:
I got the replacement for the FBT and fixed it, cleaned the PCB thoroughly and obtained the values of the burnt resistors from my friends in Technical Support Group and replaced the burst capacitor and these two resistors and also replaced the jumper wires. Replaced the PTC as it was found strained. Retouched the board from one end to another end thoroughly and then the CRT PCB. Cleaned the PCBs very well to remove flux. Lubricated the connectors, including the two insertion type sockets on the CRT PCB, for Focus and Screen Voltages.
Fixed the Front panel with two screws. Connected the board to the CRT : (1) Two connectors that come from the front panel to the board (2) Twin pin of degaussing coil (3) twin pin of Mains Cord (4) Speaker Connectors (5) CRT PCB to the CRT pins (6) Yoke connector to its pins on the board. (7) Horizontal Yoke connector to the pin near the FBT, where it was originally connected. China kits have the facility to adjust the width by selecting appropriate pins provided for 14” to 21”. As this is already explained by me in detail in my earlier article on fitting China Kit in CRT, I am not repeating it here. (8) Anode pin with cap to the anode socket on the CRT (9) Most importantly, soldered the earth wire from the earth connection behind the CRT. (10) The input board. (11) Adjusted the screen and focus voltage on the FBT to the minimum (this is essential when we replace the FBT.)
As I had already tested the power supply of the board by disconnecting the input to the FBT and giving a load of 100W Bulb in its place, I was sure of connecting the board to the CRT and see. Powered on the set, waited for the filament to glow, and then adjusted the screen voltage such that the screen is dark when the brightness, contrast, color and sharpness are at minimum. Then readjusted the brightness and contrast, after feeding a video signal and adjusted the focus for a sharp picture and then adjusted the color and sharpness for a pleasing effect. Allowed the set to run for several hours before ringing up the customer to come and collect.
The first picture you see was taken after completing the work.
For those of you who are interested, following was the uController IC in this kit, which is quite old:
Thus a completely satisfying work got added to my ever growing satisfaction 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.
Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.
P.S-If you enjoyed reading this, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!
You may check on his previous repair article below: