Samsung 65q900 main board bn41-02679b

[Benass]

Hello.
Problem, power on then off in 3 sec or something like this.
Standby light is on.

From Power supply to main board 13v is present.
Standby voltage. 3.3v 5v 1.8v.
13v drops down to 12v after diode. then it disappears.
Big aluminum plate at the back of the board prevents access to follow up 12v line.
Lots of shorts near cpu area. CPU Inductors 7 ohms.
CPU mosfets are CSD95378BQ5M
PWM ic is TPS40428 VDD is dead short no 12v standby. Aluminum plate at the back prevents future checks.

Any advice on how to figure out whats causing that 12v line short?

Sorry if i brake any rules.

[Benass]

Re: Samsung 65q900 main board bn41-02679b

Update.
Above Left CPU inductor one cap was shorted.

Restored 12v standby rail to healty 2k rezistance, but still dont have voltage.

[dskall]

Re: Samsung 65q900 main board bn41-02679b

Freeze spray and voltage injection

[Benass]

Re: Samsung 65q900 main board bn41-02679b

Thanks for your suggestions.
I already did that, found shorted cap on 12v line for cpu mosfets.
Resistance is restored on this line, but still no voltage.

The good news: customer agreed to get replacement board. So when I get it, I will document the difference For future references. Also Bios dump can be performed if needed.

Btw, this is a serious board. The similarities To pc or laptop board is striking.
It has the one could guess, ram cpu gpu.
Power rails similar to laptops. 5v 3.3v 1.8v 0.8v 1.1v etc... no wonder this TV cost 3k £

[dskall]

Re: Samsung 65q900 main board bn41-02679b

I had to look again at title to make sure it was a tv mainboard.

[Benass]

Re: Samsung 65q900 main board bn41-02679b

It is TV main board. But similarities to laptop main board is clear.


I was wondering if there is a possibility of two separate 12v rails on the board.?
or the rail itself have fuse halfway, and maybe the fuse is burned after capacitor shorted.

[Benass]

Re: Samsung 65q900 main board bn41-02679b

Update.
The board is really complicated.
Many rails low resistance. CPU rail 5-7 Ohms.

Few other rails 20 Ohms etc......

Board has few separate 12v rails. Ultimately, I was unable to fix this board.

Got a replacement board. Now replacement board wasn't powering on at the beginning, but it booted up once all connections were plugged in.

So I guess it checks for back light before powering on.