Samsung LE32S62BX probably power supply

[Kabbone]

Hey guys,
I got a Problem with the TV of the topic. I think it's related to the power supply board. It's a BN44-00192A. When I plug it in the LED just starts blinking but nothing happens and QB802 is getting quite hot after a few seconds. On the bottom it seems, that it has been shorten
I already changed a few blown parts on the board.
- BD801S: rectifier (was shorten and blew the fuse)
- several capacitors (all "big" ones)
- RM801 (was burnt)
- CM810 (broken legs)
- glue removed

The picture is the best I was able to at this light conditions, if it's not good enough I can make some better tomorrow. I will also upload a picture of the bottom tomorrow.

Any suggestions for proceeding?

[tom66]

Re: Samsung LE32S62BX probably power supply

Could be helpful to have a schematic:
http://www.tgohome.com/ServiceManual...&Search=Submit

QB802 looks to regulate a +15V supply from the main transformer for the primary side.
Test the voltage across CP811 (output) and CB806 (input.)

[Kabbone]

Re: Samsung LE32S62BX probably power supply

Thanks for your reply.
The voltage is between these two points (messured it direct at the legs of QB802) is fluctuating between a few mV and 2V

[tom66]

Re: Samsung LE32S62BX probably power supply

Was that at CB806 or CP811?
Can you remove QB802 and see if the voltage on CB806 rises?

[budm]

Re: Samsung LE32S62BX probably power supply

Please take the DC voltage reading at the two legs of CB806.
This board is know to have bad Zener Diode ZDB805 (connected to the BASE of QB802), so chek that out also.
Since RM801 is the fusible resistor that will go open if the MOSFET QM801, QM802 shorted out (QM801, QM802 are for the 24v, 13v, 5v switching power supply)

[Kabbone]

Re: Samsung LE32S62BX probably power supply

Oh I missunderstood you, thought you meant the Voltage across QB802.
I think you mean with CB806 or CP811 the collector and emitter of QB802, they are both fluctuating between 0,7V and 3V. I will test it with removing tomorrow.

[tom66]

Re: Samsung LE32S62BX probably power supply

What ground are you using?

[Kabbone]

Re: Samsung LE32S62BX probably power supply

I used the negative pole of the rectifier

[tom66]

Re: Samsung LE32S62BX probably power supply

That works fine, you can also use negative lead of main bulk capacitor if easily accessible, but I see in this case it is not.

[Kabbone]

Re: Samsung LE32S62BX probably power supply

Please take the DC voltage reading at the two legs of CB806.
This board is know to have bad Zener Diode ZDB805 (connected to the BASE of QB802), so chek that out also.
Since RM801 is the fusible resistor that will go open if the MOSFET QM801, QM802 shorted out (QM801, QM802 are for the 24v, 13v, 5v switching power supply)

Sorry, I missed your post...
QM801 and QM802 don't seem to be shorten. Over ZDB805 I got between 3V - 5V and on the base of QB802 23V

[Kabbone]

Re: Samsung LE32S62BX probably power supply

I removed QB802, the voltage at CB806 rises to constantly switching between 27V and 34V. Before with installed QB802 it had at the begining about 30V and after a few seconds fluctuation between 2-10V

[tom66]

Re: Samsung LE32S62BX probably power supply

Can you check pin 8 to ground on IC801 (probably on bottom of board)?
Also, check ZDB805 is not shorted.

[Kabbone]

Re: Samsung LE32S62BX probably power supply

Do you mean ICP801S? Which one of the pins of this controller is 1? The one at the point? If it is so, it's fluctuating between 0 - 2.5V, definitely too less isn't it?
ZDB805 isn't shorted, got 0.8MOhm

[tom66]

Re: Samsung LE32S62BX probably power supply

Sorry, yes, ICP801S.
Pin 1 is marked with a dot and the other pins are numbered anticlockwise, example:

1*****8 <-- here
2*****7
3*****6
4*****5

I should have said please test the resistance from this pin to ground, not the voltage.

[Kabbone]

Re: Samsung LE32S62BX probably power supply

The resistance is 50 Ohm. I desoldered CP811 -> it's ok

[tom66]

Re: Samsung LE32S62BX probably power supply

The IC would appear defective then. Check CP805, QP801S, RP816, RP817, RP818 and RP819. Values in schematic.

[Kabbone]

Re: Samsung LE32S62BX probably power supply

Thanks for your help. I will check the parts. Where do you get this IC? I just found it on ebay for 2€.
QP801S I checked already, it seemed ok, but I wasn't able to switch it with my multimeter.

[tom66]

Re: Samsung LE32S62BX probably power supply

I would get it from eBay, 2 euros is cheap compared to shipping cost of most suppliers. If you were making a big order of parts though (e.g. the chip plus any other resistors) I would buy it from Farnell or RS.

[Kabbone]

Re: Samsung LE32S62BX probably power supply

I did some more meassurements after desoldering ICP801S and recognized, I still have just 50 Ohm to ground at pin 8. The 50 Ohm to ground results from ICM801 Pin 15 (Vcc). This is way to less, isn't it?

[tom66]

Re: Samsung LE32S62BX probably power supply

Yes, that IC could cause the fault too.