Samsung 275T 2 seconds to black

[budm]

Re: Samsung 275T 2 seconds to black

I am not sure how close the diagram I upload is the same as your monitor, but as you can see, there are some MLCC after to fuse and also the 8-PIN MOSFET. See if it is connected as shown in the diagram.

[wetwillyskate]

Re: Samsung 275T 2 seconds to black

Its close, a couple differences are that my F601 fuse is a 3A, and i cant seem to find an F600 fuse on my board. Also CN603 is not used. Im not seeing an 8 pin MOSFET like shown in the shematic. there are other ICs nearby but i dont believe i see any FETs

[budm]

Re: Samsung 275T 2 seconds to black

From the pictures, I can see that it does indicate +5V panel so it may be for the LCD panel T-CON board, I would like to verify if the bottom end of the fuse is connected to IC604 (P/N) left pin and C402 positive pin. Also see if the trace also goes some where else.

[wetwillyskate]

Re: Samsung 275T 2 seconds to black

F601 is connected to C608 on one end as well as the pins you showed. The other end of the fuse is connected on the other side of the PCB to IC600, which is a 4435B (MOSPHET), so it is like the diagram i just needed to flip the board!

[wetwillyskate]

Re: Samsung 275T 2 seconds to black

Any new thoughts guys? I feel like we're really close to identifying the problem...

[budm]

Re: Samsung 275T 2 seconds to black

Please take the resistance reading of that IC604 right pin (left pin is connected to the fuse, middle is connected to Ground) as shown in my red line with ref to ground. I think we are getting close, just have to try to isolate the shorts.

[wetwillyskate]

Re: Samsung 275T 2 seconds to black

The left pin isn't connected to fuse F601, middle pin is connected to gnd, and right pin measures 184ohm to gnd.

It also occurred to me to measure the fuse short to gnd with the boards disconnected. with the boards disconnected the short is removed. The short returns when the CN400 connector is plugged in which connects to the board at the top of the monitor that i havent looked at yet. This a 30pin multi color connector. I will upload a pic in a sec...

[wetwillyskate]

Re: Samsung 275T 2 seconds to black

The left pin isn't connected to fuse F601, middle pin is connected to gnd, and right pin measures 184ohm to gnd.

It also occurred to me to measure the fuse short to gnd with the boards disconnected. with the boards disconnected the short is removed. The short returns when the CN400 connector is plugged in which connects to the board at the top of the monitor that i havent looked at yet. This a 30pin multi color connector. I will upload a pic in a sec...

Pics...

[budm]

Re: Samsung 275T 2 seconds to black

F601 feed CN603 (pin 1 ~ 6) per diagram, so if you remove the CN603, does the short go away also?. Where is this CN603 cable go to anyway?

That is the LVDS cable to the T-CON board on the LCD panel assembly, that 5v is for the panel T-CON board. So the short is on the T-CON board on the LCD panel assembly.
We will need the picture of the T-CON board next.
The shorts can be as simple as shorted out Multi-layer-Ceramic cap (MLCC).
We are getting CLOSE!

[selldoor]

Re: Samsung 275T 2 seconds to black

Try it first with the panel end of the connector disconnected in case the short
is within the cable - unlikely but possible.

[wetwillyskate]

Re: Samsung 275T 2 seconds to black

I dont have a C603 cable, ie it is not installed in this monitor for whatever reason. The CN400 cable is not shorted internally. below is a picture of the T-CON board. The fuse on the board is ok. I tried to disconnect the 2 ribbon cables to isolate the board, but i felt like i was going to break them.

[budm]

Re: Samsung 275T 2 seconds to black

Can you check to see if F1 is blown on that T-CON, also with the ribbon cable at the bottom of the board not connected, check the resistance between the metal body of the connector (which is connected to the circuit ground) and at the fuse.

[wetwillyskate]

Re: Samsung 275T 2 seconds to black

F1 fuse is still ok. 2.5kOhm between metal connector housing and fuse

[wetwillyskate]

Re: Samsung 275T 2 seconds to black

anyone still out there?

[wetwillyskate]

Re: Samsung 275T 2 seconds to black

so does this mean the think tank has run dry? stumped by a Samsung product?

[budm]

Re: Samsung 275T 2 seconds to black

Is the short circuit still there when you connect the LVDS cable as you have indicated before?

[ozonejunkie]

Re: Samsung 275T 2 seconds to black

I know this is a bit of an old thread, but I've just been facing a similar issue with my 275T and wanted to share my solution with anyone that may come looking.

After a couple of weeks of no use, I turned it on to find that the top backlight would light up, then the bottom, then nothing. This gave the appearance of a dimming after a few seconds.

In the end I worked out that the fault output pin on the BD9886 backlight control IC's was reporting a fault state. I am not entirely sure what was causing this fault, but I suspect that it is due to failed drive MOSFET's, as everything else is passives. (Yes, I know the fault could be in the passives, but I always suspect active's first)!

After working this out, I managed to find a replacement inverter board (GH178A Rev 9.1) for my monitor from China, and after installing this the screen is working like a charm!

Finally, thanks for the service info in this thread, it helped a lot with tracing out the board and working out what signals I was actually looking!