Samsung C32HG70 Curved Gaming Monitor - No Power

[DemonBG]

Hi all,
Preamble:
It has been a while since I have posted around here but have been quietly lurking in the background.
So, I have recently had a bit more time to tinker and so picked up 2x Samsung C32HG70 gaming monitors off eBay as a project.
First off, despite being manufactured in December 2017, Samsung are refusing to offer warranty on them, stating that it is refurbished and the warranty expired in February of 2018… less than 3 months after it was manufactured...

Symptoms:
So - The symptoms for both are that when plugged in there is no power, nothing, Nada - no standby LED and no response to any buttons.

I looked at the power board (BN44-00877B) and the 5A fuse is blown - so I bridged this with some copper wire (with the backlight LED’s disconnected) to see if could get the standby LED to come on.
This turned out to be a bad idea - as soon as the set was plugged in, the two small, white transformers (?) on the hot side of the board started smoking.

Note: Picture of underside of the board is with the larger white transformer (LPD05-6PFC) and the small transformer (SQH2210S KS-1736CAK) removed. You will also note there is some exposed trace in the upper left section of the board – Im not sure if I caused this with my fuse-stupidity or if it was like this when I got it?

There are some markings on these components: SQH2210S KS-1736CAK which I have tried to find on the internet to no avail. Does anyone know what these actually are and if there is any way to test / replace them with something equivalent?

Update 1 - I have tested all the diodes on the board (Hot and cold side) and all looking good.

Any ideas for further troubleshooting steps?

Thank you all,
Demon

[nomoresonys]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Did you open both monitors? is the fuse on the other one open too? might be easier to try and fix the one that didn't smoke first.

[DemonBG]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Hi Nomoresonys,

Thank you for the reply.

Unfortunately i dont have enough workbench space to have both open at the same time but i am currently waiting for a replacement board to come in (i could only find the 1, not 2) but i would love to find out what is wrong with the boards for reference if anyone else is having the same problem...

Thanks for the reply.
Demon

[DemonBG]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Quick update - I have been probing around and have identified that the mosfet on the left of the board (a Magnachip 60R190QS) has gone bad.

At the same time i also removed the bridge rectifier and the rectifier diode and both of these test good.

On the subject of testing, i have no idea what the black resistor looking things (with Green Orange and yellow bands) are on the board next to each of the suspect transformers (Designated SA801 and SA802). They look like they run parallel to the transformers - are these resistors?

Any help is appreciated.

Regards,
Demon

[Biruslapio]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Quick update - I have been probing around and have identified that the mosfet on the left of the board (a Magnachip 60R190QS) has gone bad.

At the same time i also removed the bridge rectifier and the rectifier diode and both of these test good.

On the subject of testing, i have no idea what the black resistor looking things (with Green Orange and yellow bands) are on the board next to each of the suspect transformers (Designated SA801 and SA802). They look like they run parallel to the transformers - are these resistors?

Any help is appreciated.

Regards,
Demon

Those are input filtering inductors,not transformers,they seem to have melted the insulation partially,bad for the board but should not cause more issues,and these SA are also inductors.
If they melted,your problem is much more probably on the primary(hot) side of the board.

[DemonBG]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Thanks Biruslapio,

Thanks for your support.

I took out one of the SA designated little black inductors and it looks like it is Open circuit. i'll check the other one today.

Im wondering if the mosfet had gone bad and when i bridged the fuse it subsequently blew / burned out the smaller black inductors (and possible the input filtering inductors?) as well.

Now the problem is getting replacement components - For the life of me i cannot find those filtering inductors (SQH2210S KS-1736CAK) anywhere!

Thank you again for your help,
Demon

[Biruslapio]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Oh,they could also be MEGAOHMs resistors,check if the color code makes sense with any resistance you measure from them,if they were inductors and are now open it was surely because of the improper copper bridge.
They filter input noise from AC lines such as harmonics,not mandatory for the board to fuction,you can still repair it.

[budm]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

SA = Surge Arrester, it should show open circuit.
No need to mess with those part, the circuit does not need those SA to function.
So the power MOSFET for the PFC shorted out, you will need to replace the MOSFET and the PFC IC at the same time, and may be the Common mode Line filter choke too.

[DemonBG]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Right you are Budm!

Thank you for the response - I took a surge arrestor from another known, good system and when it showed open circuit as well, i figured they are ok.

I am going to try and source a MOSFET and will report back here if i find anything.

I have highlighted what i assume is the PFC IC?

Without knowing what the original filter chokes are, how can i spec them?

Thank you all,
Demon

[budm]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

That is the PFC Controller IC.
"Without knowing what the original filter chokes are, how can i spec them?" Search for the replacement using P/N as printed on it.

[DemonBG]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

That is the [COLOR="Red"]PFC [/COLOR]Controller IC.
"Without knowing what the original filter chokes are, how can i spec them?" Search for the replacement using P/N as printed on it.

PDC or PFC IC? (im assuming typo?)

With regard to the filter Chokes, the internet has come up short on anything regarding "SQH2210S KS-1736CAK" which is printed on the filter chokes.


Thanks again,
Demon

[budm]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Sorry, my typo, it is PFC IC.

[DemonBG]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

So i have tried to identify the PFC IC but the only numbers i can make out are:

1762 1A5 / 1752 1A5 which i am struggling to trace on the internet. Does anyone have any idea what this could be?

thank you again,
Demon

[Immo99]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Hmm, yes I do believe these are the IC's you are looking for:

https://www.mouser.co.uk/Semiconduct...h?keyword=1762

[DemonBG]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

So the working PSU arrived which allowed me to test both monitors and confirm both have failed PSU's.

I have now pulled the second Monitors PSU and it does not have the same problem. The fuse on the second set is not blown and i have checked that there is approx 160V across the capacitors on the hot side of the board when plugged in.

Again, i have checked all of the diodes and all are working, but still i get no standby LED.

Interestingly, this board has a different MOSFET (24N60M2) and PFC IC, but again it looks like the numbers on the IC have been almost removed to the point where i can just make out "1793 1A5"

Any troubleshooting steps would be appreciated,

Demon

[budm]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

So the working PSU arrived which allowed me to test both monitors and confirm both have failed PSU's.

I have now pulled the second Monitors PSU and it does not have the same problem. The fuse on the second set is not blown and i have checked that there is approx 160V across the capacitors on the hot side of the board when plugged in.

Again, i have checked all of the diodes and all are working, but still i get no standby LED.

Interestingly, this board has a different MOSFET (24N60M2) and PFC IC, but again it looks like the numbers on the IC have been almost removed to the point where i can just make out "1793 1A5"

Any troubleshooting steps would be appreciated,

Demon

But does the power supply board have at least standby Voltage? If not, then that will be the first thing you have to fix.

[DemonBG]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Thanks for the reply Budm,

I tried probing the test point on the PSU yesterday that provides the standby voltage and it fluctuates between 3 and 9v. Any recommendations on the best place to take readings?

Thank you
Demon

[budm]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

BN44-00877B: https://www.badcaps.net/forum/attach...9&d=1544384145
I cannot read the charts on the board to see what the standby Voltage is supposed to be.
What is the standby Voltage of your working board?
Is it stable if nothing is connected to the power supply board except the incoming AC?

[DemonBG]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

Pinout voltages as requested.

I'm at the day job for the moment but will resume probing once I get home again


Thank you again,
Demon

[DemonBG]

Re: Samsung C32HG70 Curved Gaming Monitor - No Power

So i used the test point to the top left of the top side of the board which says:
"STBY: 7.5V ON: 11.5V"

Measurements with only mainboard (used the same main board in both tests) connected:

Good PSU: Standby: ~8.8V and 12.6V at power on
Bad PSU: Fluctuated between 5v and 16v & No standby LED.
Bad PSU with nothing connected , again fluctuates between 3V and 16V

Thank you again,
Demon