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

[lotas]

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.

[grimreaper420]

There is a low resistance here, as I already wrote 43 Om (0.97v), this is the power supply to the processor core, you need to determine why the fuses on the 20v led are blown, what could be shorting in this circuit... if the mosfet has a breakdown, then it has all three legs calling each other.

I retested the mosfet and did:
Drain to Source (D-S): I measured 0.417V in diode mode, which seems within the normal range for an N-channel MOSFET's body diode.
Gate to Source (G-S) and Gate to Drain (G-D): I tested for shorts between these pins and got OL for both, so there's no short between these terminals.
Based on this, it looks like the MOSFET is working fine.

I retested the capacitor and that retested fine. Could the mosfet still be bad, even after testing?

[lotas]

There is a low resistance here, as I already wrote 43 Om (0.97v), this is the power supply to the processor core, you need to determine why the fuses on the 20v led are blown, what could be shorting in this circuit... if the mosfet has a breakdown, then it has all three legs calling each other.

[grimreaper420]

If there is low resistance at point A, then check those mosfets and ceramic capacitors for short circuit first...

I tested the mosfets by putting my multimeter in continuity mode and there were no beeps from the red probe on source and black probe on drain. so i think that there is no short on the mosfet. i tested the capacitors by doing the same thing, on continuity mode and there were no beeps on the capacitors in that area. BUT quite a few of the capacitors in the red circle were beeping.

Not 100% sure if the method i used was the right way to test the mosfet.

[lotas]

If there is low resistance at point A, then check those mosfets and ceramic capacitors for short circuit first...

[harp]

ive checked a few guides on youtube to test mosfets but everyone seems to have a different method, with some more accurate than others. is there an accurate way to test it by using just a multimeter and without having to remove the mosfet?

Yes, in repair is often use these fast onboard check, put your multimeter in diode mode (beeping mode) and check between gate and drain, gate and source and source to drain. It is the same if you check transistors. The power device like mosfet in TO252 package are very much stressed and may create a internal short, about 0.1 ohm. There must no be low reading especialy to gate. That you are looking for.

The test isnt 100% acurate, depend of shematic, but in most case work, and save lot of time. If you suspect in one, look in closely of pcb connections, and if you not find nothing reason for low ohm reading, desolder it and test separately, and redo same pcb measurements without them to compare. If you find multiple device shorted with exact reading, they may heave to be on same rail, and only one is shorted... you can pinpiont by measuring heat.

Also, if you have not hot air, you can desolderit it with iron, just put a small piece of baking paper (for making cake) between leg and pcb to separate solder while luquid, see video
https://m.youtube.com/watch?v=Khs6txY6iW4

[grimreaper420]

These fuses (LED 20v) seem to be responsible for the backlight, you need to check the resistance to ground on each side of the fuses, check the output transistors of the led drivers.
43 Ohm on the inductor may be normal, since this is power supply to the processor core, and as always it has a low value.
On IC 1, 2 the low voltage may be due to the fact that they do not receive the command (ENable) from the processor....

Tested resistance to the fuses, and i cant get an accurate enough reading, the numbers jump from 0L to 200 on both of them on sides 'B'. On sides 'A' of the fuse, they are around 23 Ohms.

For testing the transistors, i followed this video (https://www.youtube.com/watch?v=uKyYUHU-wMA). The first value is red lead on source and black lead on drain. second value is opposite, so red lead on drain and black lead on source.

1 - 8.9 / 0
2 - 8.6 / 0
3 - 8.1 / 0
4 - 8.7 / 0
5 - 8.3 / 0
6 - 8.1 / 0
7 - 8.6 / 0
8 - 8.2 / 0
9 - 8.2 / 0
10 - 8.6 / 0
11 to 14 - 23 / 23

Hopefully this makes sense. Let me know if it doesnt.

[lotas]

checked the fuses and all were fine, apart from two, circled in red. the inductors all read 0L apart from the one highlighted in 3 which had resistance of about 43ohms. tested the IC chips 1 and 2, and they read 0.755v and 0.760v.

These fuses (LED 20v) seem to be responsible for the backlight, you need to check the resistance to ground on each side of the fuses, check the output transistors of the led drivers.
43 Ohm on the inductor may be normal, since this is power supply to the processor core, and as always it has a low value.
On IC 1, 2 the low voltage may be due to the fact that they do not receive the command (ENable) from the processor....

[grimreaper420]

When I see many mosfet on boad, first check for short on every of them sd, gs, gd, second check for short on coils... also check what is going on on IC301, one leg is black...

Also check to not have shorts inside ports, usb ports especialy, I see this before on monitor. Users usualy destroy contact pushing in wrong angle, and force bent and ripup contacts crossing it together, because of weird position.

5&6 probably LED backlight

checked the ports and they tested fine. also checked the coils and there were no shorts. for IC301, that was just a bad picture, there doesnt even seem to be a leg there. but doesnt look like its missing either (see pic).

ive checked a few guides on youtube to test mosfets but everyone seems to have a different method, with some more accurate than others. is there an accurate way to test it by using just a multimeter and without having to remove the mosfet?

[grimreaper420]

You won’t find any diagrams, you don’t even have to look, check all the fuses in the area of the dc/dc converters and what voltages are at the control points relative to the ground, measure the resistance on the inductors relative to the ground....

checked the fuses and all were fine, apart from two, circled in red. the inductors all read 0L apart from the one highlighted in 3 which had resistance of about 43ohms. tested the IC chips 1 and 2, and they read 0.755v and 0.760v.

[harp]

When I see many mosfet on boad, first check for short on every of them sd, gs, gd, second check for short on coils... also check what is going on on IC301, one leg is black...

Also check to not have shorts inside ports, usb ports especialy, I see this before on monitor. Users usualy destroy contact pushing in wrong angle, and force bent and ripup contacts crossing it together, because of weird position.

5&6 probably LED backlight

[lotas]

You won’t find any diagrams, you don’t even have to look, check all the fuses in the area of the dc/dc converters and what voltages are at the control points relative to the ground, measure the resistance on the inductors relative to the ground....

[grimreaper420]

bit more information

The power supply connects to the main board. There is like a checkpoint on the mainboard that says 20v, and i tested that with a multimeter and i can confirm that I'm getting 20v in. There are a few ribbon cables coming off from the mainboard to the T-CON. I tested those voltages, and those are really low. Less than 1v.

I attached a picture of the main board.

1 - 20v power cable directly from PSU
2 - ribbon cable going to TCON - LOOKS LIKE CORRECT VOLTAGE IS OUTPUT
going to TCON - DOESNT LOOK LIKE CORRECT VOLTAGE IS OUTPUT (<1V)
4 - cable leading to power button and LED backlight (BACKLIGHT DOES NOT WORK, BUT POWER LED DOES) (DOESNT LOOK LIKE CORRET VOLTAGE IS OUTPUT (<1V))
5 & 6 - labelled LED, not exactly sure where this goes

[grimreaper420]

hey guys,

i bought 2 samsung odyssey g9's for a decent price. they both have the exact same fault. when plugged into a power source, the blue led powerlight shows, but when turned on there is no picture, no backlight, no menu, nothing. when plugged into a laptop the laptop recognises the monitor, but keeps disconnecting and reconnecting.

dont have any schematics or diagrams unfortunately. any ideas?

thanks