No Power In Singer LCD TV Repaired
This Singer LCD TV 32 Inch came in for repair with the complaint of no power. My initial though was probably the main fuse was gone, together with some of the components. Well, the moment I lifted up the TV cover, I saw two separate switch mode power supplies in the power board. On the right side is mainboard.
When you see two separate power supplies in a single board, this means one of the power supply section (usually the smaller one) would be the stand by power supply. The bigger section will be the main power supply. If the stand by power supply does not work, the main power supply also would not be able to work.
So the first thing to do is to check for the DC output of the stand by power supply. Normal TV stand by power supply voltage would be 5 Vdc but this model has an output of only 3.3 Vdc. When I measured the output it was Zero volt! This usually indicated the stand by power supply section have problem.
What I did next was to check on the components in this power supply and all seems to be working fine. I forgot to tell you that the main fuse was Ok too.
It left only the stand by Power IC that I did not check.
The next step was to direct replace the stand by Power IC and retest since I have the stock with me (see the two photos below):
The standby power IC part number was FSQ510 and you can check the datasheet in the below photo:
Click on the above link to access the FSQ510 datasheet
Once the new stand by power IC was replaced and powered On, I checked on the output and it showed 3.29 VDC which is very near to 3.3 volt. As expected, the moment the 3.3 VDC present, the main power supply also work and in one of the DC output line, it showed 23.7 volt in which it was very near to 24 volt. This 24 volt is to power up the inverter circuit. The display appeared too and I was very happy with the result.
Conclusion- If you have been repairing switch mode power supply for certain amount of time already, you will be able to solve this kind of fault fast. If you already have some experiences in electronics repair and not so confident in repairing switch mode power supply, I can suggest that you get Jestine Yong’s SMPS repair ebook as he had truly layout his repair secrets on how to troubleshoot and repair SMPS successfully. As usual, will see you again in the next repair article.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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