Philips 43PUH4900/88 will not power up

[HellasTechn1]

Hello dear people.

I have a Philips 43PUH4900/88 tv set that a few days ago blew some of it's backlight LED's. Other than that, it worked all right. Before i dissasemble the panel i measured that the PSU output voltages checked ok. I ordered replacement LED bars and after installing them, the tv set will no longer power up. The pilot lamp on the front stays dark. I measured the voltage on the main filter capacitors C9802 and C9803 and they read 320VDC. I think that's a little low. I think it should be around 360-370VDC. The output reads 0V on all pins. No standby voltage, nothing. The PSU model is : TPY 715G6677-P02-001-002S
Here is a link to download the PSU's service manual from EleKtroTanya

It is weird that it stoped working right after replacing the LED's. What can i say...
What sould i check next ?

THANK YOU !

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

Good day again!
Any ideas ?

[yokoono]

Re: Philips 43PUH4900/88 will not power up

The voltage on the filter electrolyte increases to approx. 400v when power supply starts and the pfc circuit is activated. So the power on / off voltage is missing. If the stb LED does not light up, there may be problems with the stb voltage.

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

I am looking at the primary side of the psu on the schematic. Ive noticed the (U9901) Automatic X Capacitor Discharge IC. I think that it does not work since the main filter caps take forever to discharge. I measured them like 190VDC after 24 hours or so. I am not sure that would affect anything though.

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

All right now if i am reading the schematic correctly the stand by voltage is generated by (U9305) AOZ3015AL via the (T9301) power transformer. So if i lack the 12VS that feed (U9305) i will sequentially not have standby voltage and the problem coyld be either the PWM controller/mosfet or the transformet itself.
If i do have the 12VS then the problem is (U9305).
Am i in the right path ?

[R_J]

Re: Philips 43PUH4900/88 will not power up

Are you getting any voltage at all on the +12VS supply? if no voltage, check the primary circuit:
with power disconnected, check the value of R9312 (it should read like a short), if it is ok, apply power and check the voltage ACROSS C9304 (or you must use hot ground for the meter negative lead) post the voltage
Then check the voltage across C9305. This should indicate the state of U9301.

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

Hmm my psu is different than what i see on the schematic. (U9305) and (U9303) do not exist on my board.
Now (R9312) is indeed practically a short circuit and C9305 reads 0.2V.

[R_J]

Re: Philips 43PUH4900/88 will not power up

With no vcc voltage (C9305) the circuit won't work. Check for a short across C9305/C9306 if no short, check the values of R9301~R9303 & R9304 if installed. The vcc pin of the ic needs a minimum of 8VDC to start up.

In this model it is likely the main board is supplied 12vs (no U9305) as standby and all the lower voltages are supplied on the main board itself

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

When i performed my initial check before the problem came up, i think i measured 5.5 but i am not really sure since i didnt pay too much attention due to the fact that it worked.

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

In this model it is likely the main board is supplied 12vs (no U9305) as standby and all the lower voltages are supplied on the main board itself

Yes, most likely

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

With no vcc voltage (C9305) the circuit won't work. Check for a short across C9305/C9306 if no short, check the values of R9301~R9303 & R9304 if installed. The vcc pin of the ic needs a minimum of 8VDC to start up.

In this model it is likely the main board is supplied 12vs (no U9305) as standby and all the lower voltages are supplied on the main board itself

C9035 and c9036 are not shorted. I have not removed and measured their capacitance and ESR but they are not shorted.

R9301 through R9303 are marked 334 and read around 330K but according to the schematic they sould be 750K (obviously marked 754) Is this because the schematic is does not fully match my PSU variant ?

[R_J]

Re: Philips 43PUH4900/88 will not power up

The resistor values should be whatever is installed on the board, The main B+ (325vdc) should be at the end of R9301 and drop as it goes through R9302 and then R9303 to feed the ic VCC for it's initial start up.
Did you also check R9304 (0Ω)
Is it a LD5532 on your board or is it something different?

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

Good day !

Im pretty sure that R9304 (0Ω jumper) is good but i will re check.
I am also going to check the LD5532 .

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

Im sorry it's taking forever to write back. Ive been really busy. Ill get back soon. Thanks.

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

Okay, ive checked the power board. Indeed it has the LD5532GS on it. I used my DMM to measure the voltage between pins 4(GND) and 6(VCC) and i get a voltage swinging from 9V to 12V DC...

[R_J]

Re: Philips 43PUH4900/88 will not power up

Are C304 and C9305 good? What is the voltage across C9304 and C9305?
Are you getting any voltage across C9320 in the secondary?
In post #7 you measured .2v across c9305, that could not have been correct or it was with the board not plugged in.

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

Are C304 and C9305 good? What is the voltage across C9304 and C9305?
Are you getting any voltage across C9320 in the secondary?
In post #7 you measured .2v across c9305, that could not have been correct or it was with the board not plugged in.

You mean C3904 right ? Yes they are both in good condition and with ESR well within specs.

I am going to re-check the voltages because it is possible i made a mistake the other day. I am also going to use an O-scope and post the readings.

[R_J]

Re: Philips 43PUH4900/88 will not power up

The voltage across C9305 (10µf/50v) will come from the resistor divider R9301~R9303, when the circuit is operating, D9302 R9307 will charge C9304 to keep the circuit operating.

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

I took out my Oscope and took pictures of the supply pins of LD5532GS and C9304.
They both have a nice and steady 12.1V supply.
I dont know why i saw a swinging voltage with the DMM...

Here are the pictures:

[HellasTechn1]

Re: Philips 43PUH4900/88 will not power up

Thank you so much R_J. this is a great opportunity for me to get to gnkow a few rhings about TV psu's. Your guidance is much appreciated !

I look forward to hearing the next step.