Samsung LA26R71BA cannot power up

[john_doe]

Hi,

I have a Samsung LA26R71BA that cannot power up. When I press the power button on the remote, a red light on the TV lights up and then off.

Where should I start to check?

Thanks.
John

[budm]

Re: Samsung LA26R71BA cannot power up

So are you saying you are not getting DCV output at all, not even the standby DCV output?
Did you check all the fuses?
I also see bad brown glues that must be removed.
There are also lots of threads for this BN44-00192A, just search the B.C. forum for them.

[john_doe]

Re: Samsung LA26R71BA cannot power up

The fuses are all checked and ok. There is 5v on the standby pin. All other pins has 0 volt.

Which are the components I should check on the power board?

[john_doe]

Re: Samsung LA26R71BA cannot power up

The voltages I got from QM801:
Pin 1 to negative of big cap is 340v
Pin 2 is 0.5v
Pin 3 is 0.5v

And for QM802:
Pin 1 to negative of big cap is 0.5v
Pin 2 is 0v
Pin 3 is 0v

Does it means QM802 is faulty?

[john_doe]

Re: Samsung LA26R71BA cannot power up

Sorry, wrong pin number.

It should be this:
The voltages I got from QM801:
Pin 1 to negative of big cap is 0.5v
Pin 2 is 340v
Pin 3 is 0.5v

And for QM802:
Pin 1 to negative of big cap is 0v
Pin 2 is 0.5v
Pin 3 is 0v

Does it means QM802 is faulty?

[john_doe]

Re: Samsung LA26R71BA cannot power up

I swap QM801 with QM802. There is still 340vdc at pin2 of QM801. So both IC are ok.

Before the swap, there is no red standby light. After the swap, the red standby light turns on.

I attach the schematic.

Any help?

[john_doe]

Re: Samsung LA26R71BA cannot power up

Anyone can suggest anything?

[dick_barton]

Re: Samsung LA26R71BA cannot power up

Do you have 5.2V standby and if you have what voltages do you have on the pins of ICM801

[budm]

Re: Samsung LA26R71BA cannot power up

So is the PS-ON present? Since you are getting only around 340VDC it is telling me that the PFC Boosted Voltage is not working otherwise you would have about 380~400VDC between the two legs of the main filter cap, so it is either the PS-ON is not present or the PFC is not working.

[john_doe]

Re: Samsung LA26R71BA cannot power up

ICM801
Voltages at all pins are 0vdc, except:
Pin 9 0.048vdc
Pin 11 0.046vdc
Pin 15 0.046vdc

PS ON not present. Only have standby power 5.2vdc.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

If you disconnect the main board and connect PS_ON to 5.2V DC using a 1K resistor, do your other voltages come up ie +12V, +13V, +24V, +5.3V as on connector CNM801

[john_doe]

Re: Samsung LA26R71BA cannot power up

With PS_ON connected to standby 5.2vdc, all voltages are still 0vdc.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

With your meter set to dc volts can you check what voltage you have between pin 6 (black probe) & pin 8 (red probe) on ICP801S when 5.2V is connected to ON/OFF with main board still disconnected.

[john_doe]

Re: Samsung LA26R71BA cannot power up

I cannot find ICP801S on the power board, although it is on the schematic. I can see ICB801S.

[budm]

Re: Samsung LA26R71BA cannot power up

https://www.badcaps.net/forum/attach...7&d=1478264760

It is 8-pin SMD located at top right of the board as shown in the picture.

[john_doe]

Re: Samsung LA26R71BA cannot power up

Thanks budm for the location. I was looking at the wrong side. Stupid me.

I blown the fuse FP801S. Got to wait for a few days for the new fuse.

Please bear with me.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

Using a 1K from 5V standby to Power ON/Off, can you check the dc voltage across resistor RB805 and also RB807 and then with the 1K removed. Test with mainboard disconnected from supply.

[john_doe]

Re: Samsung LA26R71BA cannot power up

I cannot do any testing because the fuse FP801A keeps blowing. As soon as i switch on the power, the fuse will blow instantly.

This only started when i started to probe ICP801S. Now pin 6 and 7 are shorted. Is this normal ?

[vinceroger69]

Re: Samsung LA26R71BA cannot power up

you may need to replace that icp8o1s (remove the ic and test again for shorts on those pins once removed from the pcb) also consider building a dim bulb tester as it will save you blowing more fuses/parts.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

It's probably the IC but check DZP801 to see if that is short circuited which would also put a short across Pin6 & 7