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Philips LCD no DC voltage in output

Hi guys,

I'm new in the forum and this is my first time I ask for some help in TV issues.

My PHILIPS 42PFL5604H / 12 after some minutes, it turn off instantly with a electrically pop sound comes from the rear.

Now, I uncover the back of the TV to check the power supply for bad capacitor, but there isn't no bulk capacitor. The fuse isn't broken, I check it with a tester.

Here, you can find a video of the problem:

https://drive.google.com/open?id=1F3Bddi...

And, here a photo of the Power Supply (LGIT -> PLHL-T845A | PLHL-T813A):

https://drive.google.com/open?id=15cMC69...

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Thanks to everyone for the help.

Update (05/24/2020)

When the TV was turned on, I shutdown it with the power button on the remote control, unplug the 2 cable from PSU to MainBoard, and test the two pin (Standb, 3V3Stdby.) The result is:

3V3Stdby -> 3.25 V in DC

Standb -> 2.63 V in DC

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If the TV is power on, I can listen some noise from the Blue Transformer (INVERTER) that you can listen here:

Blue Inverter Noise: https://drive.google.com/open?id=1X3jbQI...

When the TV power off, it seems wants to turn on and the rear panel and the LED attached to the PSU board, blinking an flashing a couple of times, and after this no power goes to the Main Board.

A video of this behavior can be seen here: https://drive.google.com/open?id=1MVkILR...

I try to check, with Multimeter set to the Alternate Current Measure, the flow of current from the 244 Volts A/C Input. The big capacitor is ok, and I check also the bridge rectifier and also seems ok (when I checked it, the voltage in middle pin associated to alternate current is 244 V)

Update 2 (05/24/2020)

Due to strange measurement, I check the path that connect Standb and 3V3Stdby. I upload some images with some draw.

Rear PSU, Main Board connector part:

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Front PSU, Main Board connector part:

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Update (05/25/2020)

To better understading the connection between components, here you can see the photo of the back pannel of my TV.

The Red Light is connected to the Main Board. Sometimes it turning on, when I plug the A/C Input cable, some times not. When the A/C Input cable and no cable appear, the 3V3Stdby and Standb are equal to 0.0V. When it turn on, the values are:

3V3Stdby: 3.25

Standb: 2.65

This because, as @jayeff said in comments, “The two leads are connected to the same opto-coupler“, so the diode cause loss voltage between the two pins

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@gianlucarbone as @jayeff already pointed out this does look/sound like a power board issue. I would try to remove the back cover from your TV (Keep your hands out of it) and turn it on. Then watch to the boards to find out if you see some spark or where the noise comes from. This does sound like a bad transformer. Also, consider removing the power board and take a look at the back side. Let's see if there are any marks etc. on it. Check around the bridge rectifier etc. Let us know what you find out.

par

@oldturkey03 I have done a video for check the connection in the back side of the power supply. I will post it in another answer. I need to use link of google drive because they are very huge videos in high quality to check the solder. About the transformer, I hear a little noise from the blue transformer and record in a audio file. I will post it also. Thanks for your help

par

Hi @gianlucarbone ,

I assume you measured this when there was no red standby light, is this correct?

If so, it seems very strange to me that the 3V3 Stby voltage and the Standb voltage are not the same value.

2.63V is a very odd value to have for a reference voltage to be sent to the mainboard. If it were also 3.25V it would be more understandable.

Maybe you should follow the path back from the Standb connector and check what components are connected to it on the Power board. Just thinking that maybe the red light doesn't come on because the mainboard doesn't get the full voltage that it is expecting, but it may suddenly be there or it is building up perhaps and then the light turns on.

Even allowing for a 10% swing from the maybe expected 3V (this is a guess by me), for the Standby voltage, it is outside that range as well.

Just what I'm thinking about this

Cheers

par

Hi @jayeff. No, I measured it after waiting the red light turns on. This behavior is strange. I try to explain what I did.

First, I plug the cable to the wall socket;

Next i waiting for the Tv turn on yourself (I cannot do anything with remote control).

When for some reason the TV is turning on, a white led blinking and then I can see image and sound, normally.

After some minutes, it turns off. But, when is on I can press the red button in remote control and turn off the tv, and I can see the red light. So, what I have done is, (after turning off the tv from remote control), make me sure the red light is present, next I unplug the cable from the Main Board to make measurements, put the black cable of the multimeter in a metallic part of the TV, and with the red cable, measure the pin (using direct current obviously). Next, I can plug the cable to the main board and the red light is on, because the power supply "doesn't became faulty". I update my question with some images about the path of the pins

par

@gianlucarbone ,

Do you mean that the red light stays on when the mainboard is disconnected from the power board when you measured the voltage? If so then it's getting a bit difficult, at least for me.

Really confusing as it seems that the two leads 3V3 and Standby are connected to the input of an opto-coupler

The two leads are connected to the same opto-coupler which separates the AC side from the DC side in the power board. That may explain the voltage difference because each lead goes back to a different point connected to the input of the opto-coupler i.e. 0.7V dropped across the diode - 3.25V -2.63V =0.62V which is close enough

So with the mainboard disconnected the voltage being seen must be coming from somewhere else in that part of the power board as the opto-coupler supplies no voltage to its' input side. The diode in the opto-coupler (really a LED) turns on its' associated transistor when current flows through the diode therefore presumably turning on (or off?) something else in the AC side of the board

par

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@gianlucarbone this is long to post as a comment but definitely a good read to check a few more things. “Power Module Repair

In the absence of any signs of operability, when the PHILIPS 37PF5604H / 60 does not turn on and does not signal anything with the control lights on the panel, the PLHL-T845A power supply module is most likely faulty. When diagnosing and repairing the power supply, after replacing the swollen capacitors of the secondary rectifier filters (if any), you must first check the mains fuse. If it is broken, check the power switch FQPF3N80. K3561 and rectifier bridge diodes for avalanche (thermal) breakdown.

It should be borne in mind that in the repair practice it is extremely rare that key transistors of the N-FET type fail for no reason that should be looked for by checking other components, for example, a breakdown of the key can provoke faulty elements of the damper circuits, either dried electrolytic capacitors or dangling resistors of the primary circuit of the PSU, involved in the stabilization process. In this case, all the semiconductor elements of the strapping of the PWM regulator chip FSQ510 (7), dezh 1207A, prk FAN7530, which should be checked by replacement, are subject to verification. of any signs of operability, when the PHILIPS 37PF5604H / 60 does not turn on and does not signal anything with the control lights on the panel, the PLHL-T845A power supply module is most likely faulty. When diagnosing and repairing the power supply, after replacing the swollen capacitors of the secondary rectifier filters (if any), you must first check the mains fuse. If it is broken, check the power switch FQPF3N80. K3561 and rectifier bridge diodes for avalanche (thermal) breakdown.

It should be borne in mind that in the repair practice it is extremely rare that key transistors of the N-FET type fail for no reason that should be looked for by checking other components, for example, a breakdown of the key can provoke faulty elements of the damper circuits, either dried electrolytic capacitors or dangling resistors of the primary circuit of the PSU, involved in the stabilization process. In this case, all the semiconductor elements of the strapping of the PWM regulator chip FSQ510 (7), dezh 1207A, prk FAN7530, which should be checked by replacement, are subject to verification.

PLHL-T845A power supply unit using the PFC (Power Factor Correction) node - an active filter of the highest harmonics of the current consumption. In fact, this is a boost converter based on the FAN7530 PWM controller, which eliminates the charge current of the electrolytic capacitor of the rectifier filter directly from the network through open diodes, when its charging current is determined by its reactance.

As a result of the operation of the converter, the envelope of the high-frequency pulses of the input current of the converter will repeat the shape and phase of the input voltage. The health of the PFC node can be indirectly judged by the presence of an increased constant voltage (about + 380V) on the capacitor of the rectifier network in operating mode.

The appearance of the power supply

Main features of the PHILIPS 37PF5604H device:

Installed matrix (LCD panel) LC370WUE (SB) (A1) code 201.

To power the backlight, the PLHL-T845A inverter is used, controlled by the OZ9966GN PWM controller (24). As power elements of the inverter, keys of the FDD5N50 type are used.

The necessary supply voltages for all nodes of the PHILIPS 37PF5604H TV are generated by the PLHL-T845A power module or its analogs using FSQ510 (7), 1207A, FAN7530 (PFC) microchips and power switches of the FQPF3N80 type. K3561. from here

Update (05/25/2020)

@gianlucarbone this seems to really go down a rabbit hole. I sourced the service manual which appears to also have the schematics you need to double check. From following this thread my first suspect is the main board followed by the power board. See if the manual will help you out Q543.3E LA, 3122 785 18443, 100629

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Hi @oldturkey03, this is a very long answer. I try to stay behind you. So, in my case, there isn't swollen capacitor visibly bad. The fuse is ok, I test it with continuity test. I check also the AC until bridge rectifier and it's ok. I will upload measurements in an answer. Thanks for your help.

par

@oldturkey03 Thank you for the service manual. I see the section dedicated to the Power Supply and no information are gived by Philips. I hope to find a solution and I will post as update here. For my opinion (I'm not expert so it can be wrong), the problem cannot came from main board, as the COLD part of the Supply have no Voltage. I mean that I have checked all the pins coming from transformer and they are 0.0V in DC. Another thing I see is that the low pins of the opto-coupler have 11V in AC.

par

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Hi,

How long do you have to wait before the standby light comes back on and that you can turn on the TV after it has shutdown?

Also the "pop" sound might just be the audio turning off as the power is removed suddenly rather than being turned off in a controlled manner when the TV is turned of normally.

If you can, try "muting" the audio and then check if the "pop" is still heard if and when it turns off.

It may be that something is overheating and shutting down the power and it doesn’t start again until it has cooled down

Given that there is no standby light after it has shutdown (I couldn’t see it on in the video after the TV shutdown) it means that the mainboard either hadn't received the voltage signal from the power board so that the light can be turned on or if it has received the voltage signal, it didn't turn it on.

I can't find the schematic for the power board but you would have to check if the standby voltage is there after the TV turns off suddenly.

A way to do this perhaps is to check for voltage on all the wires in the cable going from the power board to the mainboard when the standby light is on in the TV i.e. the TV has power connected but is not turned on and write them down.

When the TV fails and there is no standby light check again to see if any are missing or if they are all there etc.

This may be a pointer as to where the problem is, power board or mainboard.

Be safety aware if you decide to try this as there is lethal exposed voltage in the back of a TV. If you don’t know how to safely test for voltage when lethal voltages are nearby then don’t do it. Leave it for the experts. It’s not worth it.

With a lot of TVs the mainboard turns the power board on when you turn on the TV. The standby voltage coming from the power board is there to tell the mainboard that it is ready to turn on as voltage is there.

Also I had a bit of a problem looking at the video and image that you posted, they just kept "hanging" with nothing showing until it eventually came after a lot of trying.

Try posting images etc direct on ifixit. Here's how to do this. Ajout d'images à une question existante

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Hi @jayeff , yes the problem of the pop is linked to the speaker. I waiting for the power supply allow me to power on the tv and wait for the shutdown without sound on, and no pop I heard.

For the time I waiting for it to power on, it is variable.

I will check the voltage when the red light is on and i give you the results.

Thanks for your help.

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Gianluca Carbone sera éternellement reconnaissant.
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