Lenovo B50-50 (80S2) No display no Post

[toty79]

Hello friends and welcome back,sorry for my English but I'm in Italy and I'm using a google to translate

Main board CG410/CG510 NM-A681 rev 1.0

I have this Lenovo laptop under repair with strange behavior, no display at first I thought it has a corrupt bios but now after disassembling it I have doubts, the laptop turns on automatically after inserting the charger without pressing the power button, If I hold down the power button for 8 seconds, it turns off for 1 second but turns on immediately after 1 second, so you can't even turn it off, tested with and without RAM, same behavior, the power light is always on and the battery light flashes which is loading normally, CMOS reset carried out without results, external monitor also tested without changes, 3V voltage present on UC3 (SPI W25Q64FVSSIQ) carrying out some measurements to detect the presence of a short circuit, I note that there is a short circuit at the ends of PC708, and next to it PQ39 ( Mosfet N AON6764) I detect a short circuit between drain and source, if I'm not mistaken this area is used to generate the CPU-CORE voltage which is equal to 0v, the cpu is completely cold, the fan does not move at all but 5v is present, I state that these measurements are made on PCB with soldered components, being SMD I wouldn't want to mess with the soldering and restrict it to the minimum possible, any advice is well accepted and thanks in advance

The two components mentioned above can be found on page. 59 of the attached manual

[MOD EDIT] Link to schematic - https://www.badcaps.net/forum/troubl...ematic-and-bvd

[shmyzdrek]

I detect a short circuit between drain and source

Hello. How many ohms there?

[toty79]

Hello. How many ohms there?

0 ohm

Thank you shmyzdrek

[shmyzdrek]

I'm sorry but I have never seen 0 ohms on multimeters, there is always an measurement error. Okay it does not matter. You can unsolder the inductor and measure from both sides, the processor side and the source side.

[toty79]

I'm sorry but I have never seen 0 ohms on multimeters, there is always an measurement error. Okay it does not matter. You can unsolder the inductor and measure from both sides, the processor side and the source side.

It has a small percentage 00.2 ohm and as if it were a net short, so you advise me to desolder PQ39 and measure outside the circuit and then measure the circuit itself without the inductor right?

PC708 at its ends I detect the same measurement, could it be influenced by PQ39 or could it also be vice versa?

[shmyzdrek]

Desolder PL9 and check which side is short.
I think SoC is dead, but we try...

[toty79]

Dissaldare PL9 e verificare quale lato è corto.
Penso che il SoC sia morto, ma ci proviamo...

Once PL9 has been desoldered, the short circuit remains on PQ39 and also on PC708, another piece of advice Thank you very much 1) PC708 desoldered out of circuit and fine, the short remains on the PCB and PQ39 2) PQ39 desoldered externally the circuit and not shorted, the short remains on the PCB Sounds more serious than expected, thanks

[toty79]

With PL9 removed from the circuit on the CPU CORE side I have a 0.02 ohm resistor short circuit to gnd, so I assume that the game is over with a fried CPU, I'm wrong, is there still hope?