Samsung 245BW

[Sam I Am]

I recently acquired a 245BW with a no picture issue.

Took it down and did a thorough visual inspection on the PS finding an open (burnt in the center) resistor (RM801).

That didn't fix it so went on to voltage checks.

Found that 24V was not reaching the output connector.

My question is: with 6V reaching the opto (PC803S), shouldn't I be seeing something besides 0V on the other side?

I suspect a toasted opto and am simply looking for confirmation/guidance from someone with more experience in these matters.

Thanks in advance,

Sam

[retiredcaps]

Re: Samsung 245BW

In the other 245B thread, a lot of people found that resistors RB805, RB806, and RB807 were bad.

Now I notice that your board is different, but check red resistor just above the BN4-0019 to see if it is open or not.

[Sam I Am]

Re: Samsung 245BW

Thanks for the reply RC,
The red one (RB808) ohms out at 2.1. The resistors were some of the first things I checked after I found RB801 burnt.
The other 245 thread concerns itself primarily with the 173A board, not the 195A board.
Apparently Samsung decided to "update" the board by finally getting rid of the infamous F9222L chip that so many have had the unfortunate chance to become acquainted with.
I've got this board where I can power it up with everything else still attached allowing me to take voltage measurements throughout.
Just have to be real careful.
The opto has me as I am by no means an expert at this sort of thing. So any help with this is greatly appreciated.

[PlainBill]

Re: Samsung 245BW

Thanks for the reply RC,
The red one (RB808) ohms out at 2.1. The resistors were some of the first things I checked after I found RB801 burnt.
The other 245 thread concerns itself primarily with the 173A board, not the 195A board.
Apparently Samsung decided to "update" the board by finally getting rid of the infamous F9222L chip that so many have had the unfortunate chance to become acquainted with.
I've got this board where I can power it up with everything else still attached allowing me to take voltage measurements throughout.
Just have to be real careful.
The opto has me as I am by no means an expert at this sort of thing. So any help with this is greatly appreciated.

What are your questions? That is the feedback link from the output to the SMPS controller.

PlainBill

[Sam I Am]

Re: Samsung 245BW

I'm looking at 6V on the input side of the opto (PC803S) and 0V on the output side. If the opto is fully functional, what approx. voltage should I be seeing on the output side?

[PlainBill]

Re: Samsung 245BW

I'm looking at 6V on the input side of the opto (PC803S) and 0V on the output side. If the opto is fully functional, what approx. voltage should I be seeing on the output side?

That depends on the design. Typically pins 1 and 2 are anode and cathode of the LED. A common design ties the LED anode to the +5V output through a 470 ohm resistor and the LED cathode to pin 3 of the reference. The detector is a photo transistor, the emitter (pin3) is tied to ground, the collector (pin 4) feeds the feedback input of the SMPS controller. Under normal operation there should never be 0 volts across pins 3-4 nor pins 1-2.

PlainBill

[Sam I Am]

Re: Samsung 245BW

So.... would 0V at the opto output mean it is toasted? And would this also explain why I am not getting 24V at the CN85 connector?

[PlainBill]

Re: Samsung 245BW

So.... would 0V at the opto output mean it is toasted? And would this also explain why I am not getting 24V at the CN85 connector?

Which opto is PC803S? This board has four. Two are obviously for regulating the main and standby supplies. One should switch the main (24 volt) supply on and off. You should be looking at the voltage across the input pins and using that to figure out what the output should be.

PlainBill

[Sam I Am]

Re: Samsung 245BW

See pic #4.

[PlainBill]

Re: Samsung 245BW

See pic #4.

That appears to be the feedback (regulation) for the 24V supply. Those voltages could be normal for a SMPS that's being held in shut-down.

PlainBill

[Sam I Am]

Re: Samsung 245BW

Beats me in what is causing a lack of 24V output.
I thought is was the opto that was toasted.
Any ideas???

[PlainBill]

Re: Samsung 245BW

Beats me in what is causing a lack of 24V output.
I thought is was the opto that was toasted.
Any ideas???

This is a fairly typical two stage power supply, and the usual problems assisting with troubleshooting. Let's deal with the supply issues first.

When I look at the power supply I see there are two transformers bridging the hot / cold dividing line. That means there is a standby supply which is always on, and a main supply that gets switched on from the main board. This one is slightly unusual because it appears the main supply only powers the inverter. There is a third coil that indicates this has a PFC front end.

Troubleshooting a supply like this without a schematic is difficult. First, you have to establish that the standby supply is functioning. Next, you have to identify the control line that turns on the main supply. Then you have to trace the control signal back to the SMPS controller. Frankly, this is a pain even if I have the power supply in my hands.

Now lets look at the problem from my end. What do I have to work with? A few fuzzy pictures. Even the rudimentary information available from the connectors is unreadable. So I say 'Screw it!!'. If someone can't be bothered to provide useful pictures, I'm not going to waste my time.

PlainBill

[Sam I Am]

Re: Samsung 245BW

Sorry about that.

Ask and ye shall receive... I always say.

Here is the front, back, and four quadrants of the back.

[PlainBill]

Re: Samsung 245BW

Sorry about that.

Ask and ye shall receive... I always say.

In that case, I'm asking for Jennifer Aniston.

Here is the front, back, and four quadrants of the back.

On CN851? the last two pins appear to be S_B and PSON. Does either change state when the TV is turned on?

If either does, do the voltages across pins 1 and 2 of the three optoisolators in that area also change?

What is the part number for ICM801, the 16 pin IC?

PlainBill

[hijodalgo]

Re: Samsung 245BW

Here's something that might help you and others

[Sam I Am]

Re: Samsung 245BW

Well.... this is about the best I can do at the moment.

As far as the voltages:
S/B is 5.2V off and 5.2V on
PSON is 0V off and 3.2V on
Opto (PC802S) closest to CN851 at Pin #1 is 5.2V off and 1.2V on
Pin #2 is 4.6V off and 60mV on
Next Opto (PC801S) at Pin #1 is 4.9V off and 4.9V on
Pin #2 is 3.9V off and 3.9V on
(Both of these voltage readings dropped a few mV when cycling from off to on)
Next Opto (PC804S) at Pin #1 is 5.2V off and 5.2V on
Pin #2 is 4.5V off and 4.6V on
(Both of these voltage readings dropped significantly when cycling from off to on before settling at the above readings)

[Sam I Am]

Re: Samsung 245BW

Must of got distracted by Jenn.

ICM801 shows MC33067P. See attached.

[PlainBill]

Re: Samsung 245BW

Must of got distracted by Jenn.

ICM801 shows MC33067P. See attached.

Yeah. What is happening across pins 3 and 4 of PC802S?

Time to do a 'divide and conquer' move. CP801S is the large capacitor. What is the voltage across it with the power supply 'on'? If it rises to 380V, we know PC802S is functioning, and the PFC circuit has kicked in.

By the way, this would be a good time to mention that 380V DC has a real good kick to it. Keep one hand in your pocket when working with it.

PlainBill

[Sam I Am]

Re: Samsung 245BW

Pins 3 & 4 of PC802S are showing 18V with the front power button in the off position.
Pin 3 shows 19.7V and Pin 4 shows 0V with the front power button toggled on.
CP801S shows 386V with the rear rocker switch (beside the mains plug) in the on position and 165V with the front power button toggled on.

[PlainBill]

Re: Samsung 245BW

Pins 3 & 4 of PC802S are showing 18V with the front power button in the off position.
Pin 3 shows 19.7V and Pin 4 shows 0V with the front power button toggled on.
CP801S shows 386V with the rear rocker switch (beside the mains plug) in the on position and 165V with the front power button toggled on.

That sounds like a problem. I would expect to see 380V with the front power button on.

PlainBill