Author Topic: Philips 32pfs4132/12 LCD TV repair (Read 32499 times)

nForce · « **on:** August 25, 2019, 12:39:14 pm »

Hello, I would like to know, what is wrong with my LCD Philips TV. When I turned it on, I heard a bang, and now I can't turn it on. The red indicator light is not showing. So because I heard a bang I thought to myself it must be a capacitor which blew up. So I opened it up and looked at the power supply board. See for yourself this power supply board:

Here you can see that all capacitors are OK. I have measured all capacitors with the multimeter, and all capacitors are not conducting. So I have measured the resistors and one of them (marked with a green rectangle) which I think it's a 0.27-ohm resistor has a resistance of a few megaohms. So is this the problem? Why I can't see a black or brown spots on the resistor indicating that it blew up?

With the visual inspection of the board, I can't see anything which blew up, because I heard a bang. Does anyone see a problem on the board (I am not an electronics engineer)?

Thanks for the help.

Rasz · « **Reply #1 on:** August 25, 2019, 08:22:32 pm »

have you checked fuse? could be the source of bang

pepona · « **Reply #2 on:** August 25, 2019, 10:55:22 pm »

Hi, the problem is usually in the pwm controller located at the bottom of the board.
We do not see this TV model in my country but we often repair this power supply in other Philips and Aoc models.
In this link is the service manual. https://www.electronica-pt.com/esquema/func-fileinfo/64391/
If you can download it and we can continue from there.

Sorry for my bad English.

Regards
Marcos.

nForce · « **Reply #3 on:** August 26, 2019, 07:56:28 pm »

The fuse is conducting, so it's OK.

pepona, I didn't know that you can get so much detailed description from a manual. What about the resistor in the green rectangle?

pepona · « **Reply #4 on:** August 27, 2019, 01:34:47 am »

Hi, this resistor sense the current through the mosfet on the pimary side.
Normally it's a low value resistor. If it measure in the MegaOhms range the mosfet is broken and may be the pwm controller too.
I'm at home now, tomorrow at the workshop i'll see the service manual and i can help you with more precision.

Excuse me for my bad English.

Regards
Marcos.

pepona · « **Reply #5 on:** August 27, 2019, 10:59:02 am »

Please download the service manual and have a look at page 44.

Your resistor is R9101
Please check: Q9101, R9109, D9104, R9110 and R9113.

nForce · « **Reply #6 on:** August 28, 2019, 06:42:03 pm »

Thanks pepona. I will check it.

nForce · « **Reply #7 on:** August 29, 2019, 06:49:08 pm »

Hey pepona, why does this resistor don't have a wattage rating? Does this mean we can replace it with 0.25 W or 5 W. It does not matter?

pepona · « **Reply #8 on:** August 29, 2019, 07:53:38 pm »

Hi nForce, this resistor is usually 2w carbon or metal film. NEVER put an inductive one. Just to make a test you can put a 0.25w one.
Remember to check the other components that i have marked to you.
If you only change the resistor it will blow up again.

Regards
Marcos.

Rasz · « **Reply #9 on:** August 30, 2019, 12:16:00 am »

Quote from: nForce on August 29, 2019, 06:49:08 pm

why does this resistor don't have a wattage rating?

what do you mean? its right there on the attached picture, 2W

nForce · « **Reply #10 on:** September 01, 2019, 07:48:54 pm »

Sorry, I was looking at the wrong resistor.

What is Q9101? A transistor, is this our PWM controller?

Mario87 · « **Reply #11 on:** September 02, 2019, 01:17:52 pm »

Q9101 is the TK6A65D N-Channel MOSFET shown at the top of your picture in your original post, screwed onto the heat sink. Quite likely that MOSFET is responsible for the PWM.

nForce · « **Reply #12 on:** September 05, 2019, 06:49:39 pm »

Thanks, guys.

How can I check the MOSFET if it's defected? Some at the local repair shop has said to me, that I need to replace the whole power supply board, because of the lightning strike. But I don't see any marks on the board which would result from a lightning strike. Is this really the case? The fuse is OK and capacitors are also fine.

Rasz · « **Reply #13 on:** September 06, 2019, 02:41:59 am »

mosfets go short most of the time, just buzz everything on this pcb for shorts

Mario87 · « **Reply #14 on:** September 06, 2019, 06:56:45 am »

Quote from: nForce on September 05, 2019, 06:49:39 pm

Thanks, guys.

How can I check the MOSFET if it's defected? Some at the local repair shop has said to me, that I need to replace the whole power supply board, because of the lightning strike. But I don't see any marks on the board which would result from a lightning strike. Is this really the case? The fuse is OK and capacitors are also fine.

First of all 99% of repair shops don't actually repair anything, they just swap entire boards to get things working.

Next, as mentioned above, when MOSFETs fail, they generally fail short circuit between the source and the drain. You can see in your picture that the source is the pin closest to the bottom with the letter 'S' next to it and the drain is the middle one with the letter 'D' next to it. Check them with a multimeter, if they are shorted out, then you have a failed MOSFET.

You will not always see external damage to a blown MOSFET. We had one at work on a new power supply module we have developed for our new product line and due to being a first fail in a new product we went to the extent of x-ray, decapping and microsection. X-ray showed nothing due to internal shielding, the decapping revealed physical damage to the die of the MOSFET and the microsection confirmed failure between the Drain and Source due to an over-voltage event, which is quite interesting as they are rated for 400V and we only use them for 24V switching....that's still being investigated.

However, what I am getting at is that you might have failure of the MOSFET even though externally it looks fine. Check for a short between Drain and Source, then depending on what you come back with, see what the next steps would be.

pepona · « **Reply #15 on:** September 06, 2019, 05:29:21 pm »

Hi everyone,

nForce, you must first confirm if you downloaded the service manual, because there are the same power supplies with different PWM controllers.
I just repaired one in the workshop and it is not worth buying a new one because the parts are very cheap.
Could you confirm if the PWM controller is 6 or 8 pins?. Please upload a picture.
In most cases, just change the MOSFET, some resistors and the PWM controller.
And yes ..... these power supplies are very fragile against a discharge.

Excuse me for my bad English

Regards
Marcos.

nForce · « **Reply #16 on:** September 06, 2019, 07:30:30 pm »

pepona, your English is good, even better than mine.

Yes, I have downloaded the service manual. But I don't understand in your first post you said that the PWM controller is located at the bottom of the board. Which one is exactly? I don't see it. At the bottom is one massive heatsink with diodes in reverse. It looks like two transistors, but they are actually not. Is the PWM controller not in the photo?

pepona · « **Reply #17 on:** September 06, 2019, 07:45:32 pm »

The PWM controller is on the solder side. Just "behind" the MOSFET.

nForce · « **Reply #18 on:** September 06, 2019, 08:49:28 pm »

Quote from: pepona on September 06, 2019, 07:45:32 pm

The PWM controller is on the solder side. Just "behind" the MOSFET.

Oh, now I understand.

Another question: Did I check the fuse in the right way, so I did not remove it from the board, but checked the continuity of the fuse on the board?
Tomorrow I will upload the photo of the PWM controller.

Thanks, this forum is great.

pepona · « **Reply #19 on:** September 06, 2019, 09:34:39 pm »

Yes, if the fuse "beeps" it's ok.

nForce · « **Reply #20 on:** September 08, 2019, 04:41:41 pm »

Hello, sorry for my slow response.

Here is the photo of U9101, so this is our PWM controller. But it's 6 pin chip. Where can I get one? I was looking at the e-bay for PF6005AS, but I found only 8 pin chips.

How can I check a diode if it's defected?
I have checked all the elements, but the resistor R9113 which was supposed to be 1K is 0.658K. Is that OK? In the datasheet, it has no tolerance.

I would like to ask pepona, how do you know that the problem is in this PWM controller? It can be anything on this board.

pepona · « **Reply #21 on:** September 08, 2019, 05:56:38 pm »

Hi nForce, the pwm driver is "PF6005AG". I replace it with "PF6003AG" which has more driver capabilities.

It may be that R9113 is less than 1k because it is soldered.

The best practice to test diodes and resistors is simply to desolder them.

To verify the pwm controller, the correct and safe way is to use an oscilloscope + differential probe and a variAC.

If I don't have the right tools and I see that the R9101 has blown, it is certain that Q9101 is short-circuited or leaking.
First, I check the components connected between the Q9101 gate and the U9101 pwm controller: Check R9109, 9110, 9111 and D9104.
Then I check R9113 which is the one that connects R9101 and the CS (Current Sense) pin of the pwm controller.
I also take a look at D9105 and D9106.

If everything measures well, replace the PWM controller and damaged components.
If you do not have a variAC you can replace the fuse with an incandecent lamp. It is not the best but if you have a short circuit nothing will explode in your face.

In these smps the fuse never blows

Sometimes the U9102 (optocoupler) and U9103 (TL431) blowns.

I hope you understand me.
I don't know what is worse: the google translator or me

nForce · « **Reply #22 on:** September 08, 2019, 07:01:59 pm »

pepona are these https://www.ebay.com/itm/5pcs-PF6003AG-6003A-PF6003A-SOT23-6-NEW/392410252043?hash=item5b5d79430b:g:-2MAAOSwbWhdbgWb correct? These have 6 pins.

pepona · « **Reply #23 on:** September 09, 2019, 01:48:42 am »

Looks good to me

nForce · « **Reply #24 on:** September 09, 2019, 07:41:35 pm »

What does mean only 6003A or PF6003A? Are these different names for PF6003AG?


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Author Topic: Philips 32pfs4132/12 LCD TV repair (Read 32499 times)

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