Samsung 245B 00173A No power No blue LED

[redoxy]

As the title says. i am having a hard time with this board. I can confirm it is the power board as I have two of these monitors and when I swap the power boards the monitor works.
I am not a pro with circuit boards by any stretch of the word but I can follow simple instructions well and i have decent knowledge on the use of multimeter and soldering. Please do bare with me when I ask "obvious" questions

Here are what I have tried so far based on searching this platform.

1. I have replaced all 3 resistors (RB805 -7)
2. I have replaced all the capacitors besides the main high voltage capacitor (CP803)
3. I have checked all 3 fuses and they are all ok
4. I checked the CP803 for Voltage when plugged in with the main power switch (next to the 110V input in the pack) and I get 168Vdc
5. I tried to measure the voltage on the connectors (CN801) and ground (I used LUG1 and LUG2). I got 0 Volts on all of them except S_B pin where I got 0.9Vdc.
6. I also measured the voltage on connector CN803 in a similar way as I did for connector CN801. I got 0 volts on all of the connectors.
So it seems i do not have 5V and 24V

I still do not have power not even the power button blue LED.

Any ides on what I can do next or what could be the problem. I really like the monitor and it will be a shame to toss it.
Thanks in advance for the help.

Cheers!!

[R_J]

Re: Samsung 245B 00173A No power No blue LED

ICB801S is the standby ic that creates the standby voltage, there is a square fuse above it FB802S, If it is open the ic is likely bad

[redoxy]

Re: Samsung 245B 00173A No power No blue LED

ICB801S is the standby ic that creates the standby voltage, there is a square fuse above it FB802S, If it is open the ic is likely bad

Thanks for the quick reply R_J.

I checked the fuse (FB802S) next to J810 and it is ok (0 ohms).

I tested the fuse without power connected or do i need to test it with power connected?

Anything else i'm missing or what other steps can I take.

Thanks again.

[R_J]

Re: Samsung 245B 00173A No power No blue LED

You can check the voltage on the fuse Or J810, you need to have your meter negative lead on the hot ground, (negative of bride rectifier or negative of main cap CP803)
with power off, check the resistance of RB813 (1.5Ω)

[redoxy]

Re: Samsung 245B 00173A No power No blue LED

You can check the voltage on the fuse Or J810, you need to have your meter negative lead on the hot ground, (negative of bride rectifier or negative of main cap CP803)

I measure the voltage between the negative bridge of the rectifier and J810. I get 168 Vdc same with using the negative of cap CP803.

I tried to measure the voltage of the pieces in the path and the voltage stayed the same across J810, through FB802S and BB801 and the first 2 pins of TB801S.
That was about how far I could go.

Please let me know what this means and what next steps to take.

Cheers!!

[R_J]

Re: Samsung 245B 00173A No power No blue LED

This should help, You did use 68Ω for the resistors.
Using hot ground, what voltage do you have on pin7 of icb801s
other caps that could be bad are, CB810, CB808, CB872, CB806

[redoxy]

Re: Samsung 245B 00173A No power No blue LED

This should help, You did use 68Ω for the resistors.
Using hot ground, what voltage do you have on pin7 of icb801s
other caps that could be bad are, CB810, CB808, CB872, CB806

Thanks for the diagram.

Yes i used 68 ohm 1W for all 3 resistors.

Based on the searching this forum ( i have read through practically all the threads i could find on this board) it seems most boards are cured by replacing the resistors and/or the capacitors. In my case none of those has worked.

I was going to replace the ICM801S next but decided to post here for expert advice before throwing any more parts at it.

Do you think that could be the cause of my issues or there are more troubleshooting I can do before taking the route of replacing i IC.

Again I appreciate the input.
Thanks

[redoxy]

Re: Samsung 245B 00173A No power No blue LED

Sorry I replied before seeing the edit.
I will get the readings right away

[R_J]

Re: Samsung 245B 00173A No power No blue LED

Did you check RB813 (1.5Ω) ? also check the voltages on the ic, like pin 7 VCC. It is a simple circuit, the ic does most of the work, It takes the high voltage on pin 5 and internally (startup cell) should have some voltage on pin 7VCC, if there is 0 volts, check if DZB871 zener is shorted, if it is ok I suspect the ic is bad.
Once the ic starts to operate, it will supply aprox 18 volts through RB802 and DB871 (check that RB802 is not open)

[redoxy]

Re: Samsung 245B 00173A No power No blue LED

Did you check RB813 (1.5Ω) ? also check the voltages on the ic, like pin 7 VCC. It is a simple circuit, the ic does most of the work, It takes the high voltage on pin 5 and internally (startup cell) should have some voltage on pin 7VCC, if there is 0 volts, check if DZB871 zener is shorted, if it is ok I suspect the ic is bad.
Once the ic starts to operate, it will supply aprox 18 volts through RB802 and DB871 (check that RB802 is not open)

Followed the testing recommended and here are the results i got.

IC pin 7 (i wasn't sure which one was pin 7 so I measured all the pins with with hot ground from rectifier) all gave 0 volts (well some gave 0.001 or 0.002 volts).
There was 155 Vdc on the first two pins (top and bottom) on the far left (left being the side closest to the cold part of the board).

RB813 = 1.6Ω measure without desoldering
DZB871 (tiny little black 3 pin diode on the back) wasn't sure how to measure it correctly so i did a number of measurements as follow:

bottom = single pin
Left is one of 2 pins on left with bottom (single pin) pointing toward down.
Right is the other pin of the 2 pins on the same side

measurement done with MM in diode mode

-ve lead to the bottom (single pin) reads 0.594 volts to either of the two pins

+ve lead to bottom (single pin) reads open (OL) to either of the two pins.

The two pins read 0.002 volts between them.

I hope this makes sense.

Thanks

[redoxy]

Re: Samsung 245B 00173A No power No blue LED

I decided to replace the IC ICM801S. Ordered online and will be delivered tomorrow. In preparation decided to desolder the old IC so that all i have to do tomorrow will be just soldering the new one in and assembling.

However, it seems where IC located has overheated or something making the location weak (see pictures attached, also visible in the initial pictures I posted) so during desoldering, the connections seems to have lifted and the trace broken/lost (pictures attached). I realized this after the fact unfortunately.
As a note, the soldering iron wasn't the cause as the temperature is constant and I have replaced resistors and capacitors on this board with it without issues.
Is there a way to salvage the board or repair the lifted/broken areas?

[R_J]

Re: Samsung 245B 00173A No power No blue LED

Why would you remove that ic? I thought you did NOT have 5 volts standby (S_B5V)? That is ICB801s the small 8 pin ic
If this ic (ICB801s) is not working, you will never get ICM801S to turn on. That ic WAS likely good and the circuit board could have been left alone.
What did you use to remove the solder? looks like you used one of those desolder pumps that sucks the traces along with the solder, you should use a good quality solder wik. likely the solder iron is way too hot also

[redoxy]

Re: Samsung 245B 00173A No power No blue LED

Why would you remove that ic? I thought you did NOT have 5 volts standby? That is ICB801s the small 8 pin ic
What did you use to remove the solder? looks like you used one of those desolder pumps that sucks the traces along with the solder, you should use a good quality solder wik. likely the solder iron is way too hot also

I decided to replace that IC through googling and I guess my ignorance.
I used a desoldering bulb to remove the solder.

found out about solder wik after the damage
I will be ordering some soldering supplies just in case I have to this again.

The soldering iron is the same one I used to to replace the resistors and capacitors on the board (25W)

Hopefully the board is not toast and can be repaired

[R_J]

Re: Samsung 245B 00173A No power No blue LED

If you are going to google for the answers good luck. Replacing that ic will do nothing if you don't have standby voltage.

[redoxy]

Re: Samsung 245B 00173A No power No blue LED

If you are going to google for the answers good luck. Replacing that ic will do nothing if you don't have standby voltage.

Sorry R_J. I'm not trying to devalue the help you have been providing. As I said part of it is definitely due to ignorance on my part.

I appreciate you trying to help me. This is definitely not in my domain of expertise as I mentioned in the initial post. And without help from an expert like you, I will not get anywhere.

No more Googling I will just tick to this thread and forum. Please give me another chance.

After reading your post I rechecked the IC ICB801s and it seems one of the pins is not soldered (picture attached). is this normal or that is a sign of something being wrong?

[R_J]

Re: Samsung 245B 00173A No power No blue LED

If you look at the schematic I provided, you will see pin #6 NC (No Connection) You can look up (google) the pdf for the ic which is ICE3B0365J, it will explain the pinouts and what they do.
If you use hot ground, measure the voltage on pin 5, it should be min 160v DC. Then check the voltage on pin 7, It would read about 10 vdc if the ic is in shutdown mode or around 20 vdc if the ic is working. If that voltage is 0 the ic is likely dead.
This circuit NEEDS to work as it gives the 5 volt standby to the main board. AND it supplies the VCC via the 3 resistors and QB803 to the ic (ICM801S) you removed.

[redoxy]

Re: Samsung 245B 00173A No power No blue LED

Thanks R_J.
Can these voltage tests of the IC be done on just the power board on a bench or I need to have it completely connected to all the barts in the monitor to test.
At work now so I will get to it after work when I get home. I will post back the results.

[R_J]

Re: Samsung 245B 00173A No power No blue LED

Yes they can. The power supply should produce +5 volts standby, Once that is working the rest of the power supply can be tested, either by connecting the main board or forcing the PSON pin by connecting it to stby +5v

[redoxy]

Re: Samsung 245B 00173A No power No blue LED

Tested the voltage on ICB801s with a hot ground (used -ve on the rectifier). Here are the results

Pin Vdc
1= 0
2= 5.03
3= 0
4= 168
5= 168
6= 0
7= jumping rapidly between 12.4 and 14.8 give or take
8= 0

These tests were done with ICM801S still desoldered I am not sure if that has any effect on the results.

[R_J]

Re: Samsung 245B 00173A No power No blue LED

It looks like the ic is trying to start, Are you getting any voltage on the S_B5V line?
A couple things to check would be CB872 (22uf/50v) CB810 (1uf/50v) or maybe the 5 volt filter, cb876 or cb809.
Most likely would be cb872