No Power In Philips LCD TV Repaired
I received this Philips model: 32PFL3409/chassis TCM3.1 which was dead. From my past experience and bad encountered with cracked LCD panel, I find it worthwhile to put in extra work to check for crack screen before the repair by exposing to sunlight. ( photo 1).
Photo 1 –Checking on the LCD panel for crack.
Under the sun the LCD screen does not show any sign of crack or defect so I proceed with the repair work. The first thing I noticed the fuse has blown on the power supply board. Normally with blown fuse there must be at least more than one parts shorted. Surprisingly, I could not find any shorted components. When I was checking the MOSFET drivers, I noticed that there were two capacitors CW2 and CW4 facing each other side by side with black marks on the surfaces ( Photo 2). When separated, capacitor CW4 showed sign of damages probably due to high voltage breakdown since it is rated at 1KV.
Location of CW2 and CW4 on the schematic
I changed both capacitors CW2 and CW4 to higher voltage rating of 2KV with the same capacitance value. I suspect power surge more than 1KV killed the capacitors. The fuse was temporary replaced by a 100W bulb to test the power supply after repair. When power was switched on, the bulb glowed brightly for 1 to 2 seconds then goes to dim level which was a good sign. The TV sound can be heard but the backlight was not turn on even though the 24V is present and the BL-ON voltage is more than 2V.
I suspected there must be problem with the backlight high voltage inverter circuit .IC10 (OZ9976) is the backlight PWM controller IC. When I measured the input supply voltage on pin 15 the +12V was found to be missing. I de-soldered pin 15 and turn on the power again, the +12V supply line was now back to normal. IC 10 confirmed to have shorted the +12V supply line.
Backlight high voltage inverter IC 10
After replacing IC 10, the backlight turn on and the TV is operating as normal. This is a simple and straight forward repair job. Hope you enjoy reading this article.
This article was prepared for you by SK Wong from Malaysia and he graduated from London with a degree in Electronics and Electrical Engineering. He has more than 40 years of experience in the consumer product manufacturing. With the passion to repair electronic products from young , he has been doing it part time until now.
Currently, he can provide turnkey solutions for consumer products including services from idea or concept to design , prototyping , finished products (including electronic,mechanical and plastic parts) and manufacturing.
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Note: You can check his previous repair articles below:
https://www.jestineyong.com/lg-plasma-tv-unable-to-turn-on-repaired/
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Parasuraman S
June 9, 2016 at 11:52 pm
Excellent, straightforward job! Thanks for sharing!
albert van bemmelen
June 10, 2016 at 3:41 am
Thanks Mr. SK Wong for the good article complete with clear and informative Invertor schematic!
Yogesh Panchal
June 10, 2016 at 1:48 pm
well done! sir.
justice cele
June 10, 2016 at 2:17 pm
Wow very exciting Wong, thanks.
suranga bandara, Suranga Electronics
June 10, 2016 at 5:46 pm
Good work Mr -SK Wong,
You have shown your expertise.
Thanks.
henry
June 12, 2016 at 2:45 pm
Nice article and well presented too. I am finding it very helpful (and also very educational) when the article includes a schematic (even part of it) while explaining the diagnostics procedure steps and shows the location of the failing components in the circuit diagram. Thank you SK Wong and others who follow this good practice.
After all the purpose of this commendable blog is to share the knowledge, promote electronics repair art and joy, and also to provide a learning opportunity to others who are interested and want to learn.
I know that the schematics are not necessarily always available but the writers of the articles on this blog should, whenever possible, try and make an effort to include them in their presentations.
I hope other readers also see the benefit in this and agree with me.
Humberto
June 14, 2016 at 12:44 am
Hi Henry, you are right, but remember it's not so easy to solve the schematics nowadays.
Paris Azis
June 13, 2016 at 2:02 pm
Good job and interesting repair case, SK Wong. According to my experience this is rather a rare case (the failure of the H.V disk caps I mean). I believe that their original voltage rating is good enough to withstand the anticipated H.V spikes likely to appear at the drain terminal of the mosfet, but it seems that the quality of these caps was not good. Every time I face a failure in similar stages, it works like a habbit to me, I always measure the DC voltage at the snubber circuit, at the connection point of the cathode of the diode with the snubber cap. This is a vivid indication of the effectiveness of the snubber circuit which is responsible to keep the drain voltage of the swiching device at a safe level, according to the topology used. This is my main argument about the quality of those caps I referred to.
The above measurement,and perhaps further modification of the snubber network, is absolutely necessary whenever the power switching device is replaced by an equivalent instead of the original device, especially if the switch is a BJT...Anyway, this is a very long story...
Humberto
June 14, 2016 at 12:50 am
Hi SK Wong. I liked your article a lot. Keep up sharing your expertises.
Zed
June 23, 2016 at 3:33 pm
Thank you Mr. Sk Wong nice sharing of your repairs.Thanks alot.
ombra32
July 1, 2016 at 7:01 pm
Very good article..thank you!!
samuel
October 24, 2017 at 3:13 am
i greet you people in this house please i have problem with my philips 32" model 32PFL3406S/98 it does not power on no standby no backlight voltage no power entering the main board when i connect the power supply to the main board the voltages on the power supply drops eg 12v drops to 5.6v while the 5v drops to 3.3v any solution will be appreciated SAMUEL
Bates
April 8, 2020 at 7:24 am
sir, thanks for sharing knowledge. I've done replacing CW2 & CW4. Upon switch on, the 100w bulb connected to fuse keep on & off with clicking relay sound. I've notice there's two same blue caps were blacked colour located at CH1 & CH2 but cant get the caps number coz its burnt. Please advise.
Thanks in advanve
Taurai Mirimi
July 20, 2020 at 2:58 am
Great share. Thank you.
Have similar problem with a big screen tcl tv. Has a black screen but you can hear it boot. The oz9976 I suspect but the IC has a zero volt print wiring on pin 2and pin 15. The 12v is supplied on the zcs pin. I wonder how this was working. Could not find a detailed datasheet on this ic