Never Expect Just One Component Is Defective
The complaint of this 32 Inch Philips LCD TV was no power. The model number for this TV is 32PFL3406S/98. As usual, one needs to remove the cover to access to the boards. I saw the power/inverter board and also the mainboard -see the photo below. The power/inverter board is also called as I/P board.
The first thing I did was to check on the main fuse and it was found to be good. The next step I checked on the output voltage by measuring the voltages at the output connectors-see the photo below.
There were totally no voltage at all and this means the power supply board it self is the cause of the problem. If there are good output voltages, I have to check on the mainboard.
For your information the Big main filter capacitor have the DC volt and the secondary diodes were checked to be good. Now it left only the components in the primary side that need to be checked. After spending some time, I could not locate any bad components in the power primary side. There was only one component that I have not checked it yet and that component was the power IC. For your information if you want to know how to test/check electronic components like a professional you can go to Jestine’s website here.
As mentioned above the only component left that was unchecked was the power IC.
The part number is LD7591GS. Take a look at this IC datasheet and you can click on the photo below to access the pdf file.
I soldered out the power IC and replaced with a new one and powered it on the TV. Guess what? The TV came back to life as seen from the photo below:
Conclusion- There was DC supply to the power IC and I suspect it does not have the output waveform. Due to this, the power FET can’t be switched and the transformer’s primary winding can’t be energized. If it can’t energized, then there will be no power transferred and thus no power at the secondary side. In electronics repair some times you can find lots of defective components but in the above repair case, there was only one bad component. So before you repair, please do not conclude that there must be lots of bad components in the circuit board. If you want to be good in switch mode power supplies repair , you can check out Jestine’s ebook here.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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August 9, 2018 at 10:23 am
A very good professional solution! Well done!
Albert van Bemmelen
August 9, 2018 at 3:19 pm
Very good repair and article with datasheet. I keep wondering about the many different power ICs that already do exist. They all do the same thing and there is no real standard or uniformity. Some ICs are even called Green energy controllers. And this LD7591 apparently was designed for LED applications only.
August 9, 2018 at 8:42 pm
Thank for the logical and detailed repair steps. Very well done. Thank you for taking the time to document this repair and share with others on the forum.
August 10, 2018 at 1:12 am
Hi you make repairs sound so easy thanks for the interesting topics
Robert Calk Jr.
August 10, 2018 at 3:10 am
Good job Suranga, and nice photos.
August 10, 2018 at 10:02 pm
Hi Suranga, great repair and good quality images.
August 11, 2018 at 3:31 am
Thanks Suranga, it's really interesting your approach.
August 13, 2018 at 5:17 pm
THANK'S FOR SHARING YOUR KNOWLEDGE.MAY YOU BE VICTORIOUS
August 13, 2018 at 8:08 pm
I enjoy the schematic diagram, thanks Suranga great work keep it up.These articles have so much teaching impact.
Amir Mukhtar Ashrafi
August 15, 2018 at 5:00 pm
Thank you for Sharing Nice Expertise Repairing.
Also, Credits goes to Sir Jestine Yong for Lovely Knowledgeable Websiite.
Thank you Sir Jestine.
A Student of Sir Jestine
Amir Mukhtar Ashrafi