Samsung Odyssey G9 (c49g95tssr) no picture or backlight. Power LED shows

[lotas]

It's strange, maybe at that time they measured it and there was poor contact between the probes and the contacts, the fuses seemed to have blown?

[grimreaper420]

Do you have low resistance relative to ground at point A? Take a clear photo of this area.

okay something weird happened. i retested point A on the blown fuses and they both tested 23.1Ohms (like before). retested points B, but B.1 is now showing 15 - 17Ohms (changes every time i retest it, jumps between 10 - 15) and B.2 16.9 - 17.7 (wont stay in on one number). Point C is jumping between 16.9 - 17.5.

[lotas]

Do you have low resistance relative to ground at point A? Take a clear photo of this area.

[grimreaper420]

1E - (sot23 package) is a BC847A NPN transistor.

Ah okay! I retested with multimeter in diode mode
Base (red probe) to Emitter (black probe) - 0.674v
Base (red probe) to Collector (black probe - 0.667v
Base (black probe) to Emitter (red probe) - .OL
Base (black probe) to Collector (red probe) - .OL
Collector (red probe) to Emitter (black probe) - .OL

That looks okay. Next step to remove mosfets and retest?

[lotas]

1E - (sot23 package) is a BC847A NPN transistor.

[grimreaper420]

Yes, nothing criminal is visible, rather the ports are all alive, all that remains is to find out what caused the fuses to blow in the LED driver...

guess thats good news so far

I was retesting the mosfet and capacitor this morning, and they looked okay. i turned over the board to check whats on the other side, and i found this mosfet (has code 1E on it) directly below. I tested and got the results gate (black probe) to source (red probe) i got .OL but in reverse gate (red) to source(black) i got 0.673v. source (black) to drain (red) i got .OL drain (black) to source (red) i got 2.184v.

[lotas]

Yes, nothing criminal is visible, rather the ports are all alive, all that remains is to find out what caused the fuses to blow in the LED driver...

[grimreaper420]

I don't understand your numbers, there shouldn't be low (not some Om) resistance on these lines relative to ground, they usually show as a diode when changing multimeter probes...
57 is this Om, kOm, mOm?

It's easy to check there, they are all connected to resistors.

okay, in diode continuity mode i got the readings

1.755v, OL, OL, OL, OL, OL, OL, OL, OL, OL

1.563v, OL, OL, OL, OL, OL, OL, OL, OL, OL

1.564v, OL, OL, OL, OL, OL, OL, OL, OL, OL

does that make sense?

[grimreaper420]

I don't understand your numbers, there shouldn't be low (not some Om) resistance on these lines relative to ground, they usually show as a diode when changing multimeter probes...

ah i think i tested wrong. i tested for continuity in manual mode and not 'diode' mode. i will retry in diode setting

[lotas]

I don't understand your numbers, there shouldn't be low (not some Om) resistance on these lines relative to ground, they usually show as a diode when changing multimeter probes...
57 is this Om, kOm, mOm?

It’s easy to check there, they are all connected to resistors.

[grimreaper420]

they were quite difficult to test but ive got a few results from them

(going from left to right from the picture you attached)
61.6, 61.7

OL, OL, OL, OL, OL, OL, OL, OL

220, 245

58, 58, 57, 57, 57, 57, 57, 57

247, 247, 57, 57, 57, 57, 57, 57, 57, 57

[lotas]

These are the ones that go straight into the 8+2 processor.

[grimreaper420]

Then you need to check the signal lines at the HDMI and DP inputs for resistance relative to ground, if you connected it “hot”, that is, the monitor was connected to the network and the source too, and when connecting the connecting cable, a discharge could occur and then the processor would die, or maybe there was lightning ...

I tested the pins anyway (on the HDMI port) and my results were pin 1 - OL, pin 2 - 1.1, pin 3 - OL, pin 4 OL, pin 5 1.1, pin 6 OL, pin 7 OL, pin 8 1.1, pin 9 OL, pin 10 OL, pin 11- 1.2, pin 12 OL, pin 13 OL, pin 14 OL, pin 15 61.7, pin 16 61.1, pin 17 12.23, pin 18 14.71 and pin 19 OL

[grimreaper420]

Then you need to check the signal lines at the HDMI and DP inputs for resistance relative to ground, if you connected it “hot”, that is, the monitor was connected to the network and the source too, and when connecting the connecting cable, a discharge could occur and then the processor would die, or maybe there was lightning ...

Ah okay! How do I know which lines at the ports are signal lines? Are the pins layouts on all HDMI and DP ports the same?

[lotas]

Then you need to check the signal lines at the HDMI and DP inputs for resistance relative to ground, if you connected it “hot”, that is, the monitor was connected to the network and the source too, and when connecting the connecting cable, a discharge could occur and then the processor would die, or maybe there was lightning ...

[grimreaper420]

Does the second motherboard (second monitor) have exactly the same problem or have you not taken it apart yet?

the second one has the exact same problem. i've given that one to a electronic board specialist, who said he will have a look. hes still got that one. he didnt seem confident in repairing it, which is why im trying to learn and repair at the same time

i'm not sure what happened to them, but i think the previous owner must have them both running together. probably explains why they both have the same fault.

[lotas]

Does the second motherboard (second monitor) have exactly the same problem or have you not taken it apart yet?

[grimreaper420]

It has a built-in diode, if in doubt, then unsolder it and check it.

yes sir. will take me a few days to unsolder and check it, but once i have, i will let get back to you

[lotas]

Retested the mosfet and it showed the same 0.417v on and off. No shorts. I didn't realise, but it is actually a P-Channel mosfet. The code is 4447A and online documentation says "30V P-Channel MOSFET". Would the next step be to remove the mosfet and recheck, or move our attention onto somewhere else?

It has a built-in diode, if in doubt, then unsolder it and check it.

[grimreaper420]

You could simply charge the mosfet with a multimeter and it would open and begin to conduct, you need to bridge all the legs with something metal and check again.

Retested the mosfet and it showed the same 0.417v on and off. No shorts. I didn't realise, but it is actually a P-Channel mosfet. The code is 4447A and online documentation says "30V P-Channel MOSFET". Would the next step be to remove the mosfet and recheck, or move our attention onto somewhere else?