Samsung LE32B450C4W bad PSU

[HellasTechn1]

Hello friends,

I have this Samsung LE32B450C4W television that would blow the PSU main fuse when connected to MAINS.

I found the bridge rectifier Shorted and a blown mosfet (QP802s K10A60) i replaced both (actually the K10A60 with a K15A60) and the mainboard comes on. I hear the startup sound but the backlight does not come on at all, not even for a second.
A friend of mine with the same tv lend me his PSU (slightly different components than my) and so my samsung worked all right. So i know ccfl lamps are ok and that something else is wrong with my PSU. i have measured all capacitors and transistors (heat sink mounted) also i replaced the sem2006 but nothing changed.

Any advice ?

thank you so much !

[jondoe]

Re: Samsung LE32B450C4W bad PSU

Get some pictures of the top and bottom of the PSU up, part numbers for the board and voltages from the boards output.

[ReeceyBurger123]

Re: Samsung LE32B450C4W bad PSU

Some voltage testing would be nice dont you think.....

[HellasTechn1]

Re: Samsung LE32B450C4W bad PSU

Will do both. thanks. Be back soon.

[HellasTechn1]

Re: Samsung LE32B450C4W bad PSU

I have taken pictures and measurements.

Here is a table exactly as shown on the PCB but with the readings i got.

as far as i can tell DET_5V is wrong and i am not sure about I-PWM and E-PWM.

[dick_barton]

Re: Samsung LE32B450C4W bad PSU

Check this out.

[budm]

Re: Samsung LE32B450C4W bad PSU

Since the PFC Voltage booster MOSFET shorted out so more likely the PFC IC is also damaged.
Do you have about 380 VDC between the two legs of the main filter cap when the TV power switch is activated?

[Dumah Brazorf]

Re: Samsung LE32B450C4W bad PSU

Do you see image using a flashlight and ear audio?
Check the resistance of the 2 ccfl trasformers.

[HellasTechn1]

Re: Samsung LE32B450C4W bad PSU

Since the PFC Voltage booster MOSFET shorted out so more likely the PFC IC is also damaged.
Do you have about 380 VDC between the two legs of the main filter cap when the TV power switch is activated?

At first i suspected theIC but now since mainboard is getting voltage does'n that mean that the ic is ok ?
I think that sice the ic is driving the transformer if it was bad then i would not be getting any voltage. Am i not thinking right ?

I get 300V on the cap when stby and 280V when mainboard is ON.

Do you see image using a flashlight and ear audio?
Check the resistance of the 2 ccfl trasformers.

CCFL's are good. I know that for sure and yes i can see picture with a flashlight. I will have to unsolder the transformers and check them.

Check this out.

Thank you. I think theese diodes are all right since i get voltage on the main filter cap.
I am sure i have checked them but i will check again just to make sure.

[vinceroger69]

Re: Samsung LE32B450C4W bad PSU

i would check/change the pfc ic 280 volts is too low as budm suggests should be 380vdc

[budm]

Re: Samsung LE32B450C4W bad PSU

At first i suspected theIC but now since mainboard is getting voltage does'n that mean that the ic is ok ?
I think that sice the ic is driving the transformer if it was bad then i would not be getting any voltage. Am i not thinking right ?

I get 300V on the cap when stby and 280V when mainboard is ON.




CCFL's are good. I know that for sure and yes i can see picture with a flashlight. I will have to unsolder the transformers and check them.


Thank you. I think theese diodes are all right since i get voltage on the main filter cap.
I am sure i have checked them but i will check again just to make sure.

The PFC Voltage booster is not working. When in standby, the DCV between the two legs of the cap should be = to 230 VAC x 1.414 = around 325 VDC, and when the PS-ON signal is present then the Voltage will get boosted up to >380V (but <400 VDC).
You should verify that for sure you only have 300 VDC on the cap, that is low for standby unless you incoming AC is low.
The lost of Boosted Voltage can be due to PFC IC is bad or not getting the VCC to run, or bad PFC Diode (check for leakage resistance) as shown in the PDF in post #6.

[budm]

Re: Samsung LE32B450C4W bad PSU

Some reading about PFC.

[HellasTechn1]

Re: Samsung LE32B450C4W bad PSU

Thanks i am getting into it right now ! I will get back as soon as i am done checking.

[HellasTechn1]

Re: Samsung LE32B450C4W bad PSU

The PFC Voltage booster is not working.

One silly question just to make sure...

the PFC IC is the (FAN 7530) right ?

[vinceroger69]

Re: Samsung LE32B450C4W bad PSU

yes thats the pfc controller ic

[HellasTechn1]

Re: Samsung LE32B450C4W bad PSU

I ordered the PFC chip and i should be getting it by saturday or monday.

After i get it and solder it i will report back the resaults.

Many thanks to all of you !!!

[vinceroger69]

Re: Samsung LE32B450C4W bad PSU

did you check the diode as mentioned in post 6? if not i would test/replace it too.

[HellasTechn1]

Re: Samsung LE32B450C4W bad PSU

Yes i have. They are within specs. for example the 1N5408 gave me
max reverse current 2na , breakdown voltage 663mv and capacitance 90pf

[dick_barton]

Re: Samsung LE32B450C4W bad PSU

What dc voltages do you have on the following pins of SEM2006
PIn 5 (DET) =
Pin 14 (VCC) =
Pin 17 (Fail) =

[HellasTechn1]

Re: Samsung LE32B450C4W bad PSU

Ok. i havent checked theese but at the moment i have undoldered the PFC chip from the board and i am waiting for the new one so unless i re solder it on, i dont think i will be able to measure the sem2006.

I think i may receive it tomorrow or saturday so i gess i will have to wait a bit.

I will get back to you as soon as i have news !

DET on the psu connector gave me 1v. i dont know if that is the same as sem2006 pin5