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Hemilton CRT TV with vertical problem. Model HEM 433

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This is a made in China CRT TV set and was brought to my shop with a vertical deflection problem. Usually a vertical problem is shown on TV screen with a black screen and a line across the screen.
Most of the time, you can turn the TV and you could see the vertical line across the screen but in my case here, the TV was dead. I could not turn it on. The customer told me that a line across the screen came on and then the TV went dead.
I could read the 300 volts on the main capacitor and 124 volts was reaching the horizontal transistor. There was no high tension present and the stand by light was on but the TV was dead. From experience, I have seen it happen so many times that when there is a dead short in the vertical IC itself, it could affect the whole TV and in this case the TV was dead. To confirm my analysis, I checked the 25 volts coming out of the secondary section of the power supply and they were missing. The vertical IC has a dead short in it that it was pulling the 25 voltages down to 1 volts only. How did I know which ACC leg to look for to read the voltages? The only way to know is by checking the specification of the vertical IC online and you will know which leg that is getting the power. In my case, the vertical IC LA78041, leg number two was the power feed to this vertical IC.
The moment I soldered out the vertical IC, power came back to the set and I could see the vertical line across the screen. And I could read the 25 volts on the printed circuit. It is always a good idea to check for bad capacitors around the vertical IC. In my case, I found 6 bad capacitors there. Three capacitors 220uf/35 volts and three capacitors 450uf/16 volts. I replaced all of them.
I replaced the vertical IC and the TV came alive and I could see a picture but there was something wrong with that picture. The blue color was missing in that picture. Usually, there are too things to look for in such a case.
1- The blue color filament in the CRT neck is not working right. Usually there are three light in the neck of the CRT tube. Sometimes you could see them there if you dim the light in the room.
2- The transistor for the blue color in the CRT board is bad.
To my luck, when tested the transistor, it was shorted out. It was BF422. The moment I replaced that transistor, the blue color was restored.
It was lots of work but at the end, I won the challenge and the joy to see that TV come to life was wonderful.

working in the bethlehem area in Palestine. repairing electrical and electronic equipment. for any questions or comments, do not hesitate to drop me a note on wrishmawi@hotmail.com

This article was prepared for you by Waleed Rishmawi, one of our 'Master Authors'.
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Published in our category of CRT Televisions on Sunday September 16, 2012 with the keywords , , , .
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