Lenovo 510-15isk - No display & restarting

[Flewmp]

Hello Badcaps,

I have a friend's Lenovo 510-15ISK(80SR) which he asked that I look at.

Specs:

CPU: Intel Core i5 6200U
GPU: Nvidia GF940MX (N16-GTR-S-A2)
RAM: Single Samsung 8GB DDR4 2400MHz module
Storage: SATA 2TB HDD
Motherboard: NM-A751 Rev1.0(LCFC/Compal?)

A bit of background, as told to me by my friend:

The laptop was dropped, which caused the display to stop working. The device was brought to a repair shop, which performed a repair; thereafter the device worked normally for a month. One day the screen froze, so my friend turned the notebook off. When attempting to turn it on, the power-on indicator LED on the side of the device would come on, but the display would remain inactive(no picture or backlight). He then returned to the repair store who indicated that they thought it was a motherboard fault and that there was no solution except to change the board entirely. They had the device for two months and eventually told him that, despite "changing the motherboard 3 times", they could not repair the device. In their opinion, it cannot be repaired. He then brought it to me to see if I can help.

Observations:

- AC adapter voltage is within spec.
- Charging LED illuminates when the adapter is plugged in.
- When powering the device the power-indicator LED, CPU/GPU fan, and keyboard backlight are working.
- The keyboard CAPS key LED does not illuminate when the key is pressed.
- The device remains powered for approx. 15 seconds and then restarts.
- The CPU fan speed increases several seconds before the device restarts.
- HDD is inactive/not spinning.
- No display, or display backlight.

- Visual inspection under a microscope doesn't show any obvious damage on the board.
- Probing the inductors, 5V, 3V, 1.8V rails are present.
- CPU Vcore is 1.010
- Probing caps under GPU, 0.901V.
- LCD connector(JEDP1) has 20V and 3V present on respective pins.
- Checked PU701 (+1.05VS), PU602(+1.5VS), PU702(+1.05VSP_VGA) and PU601(+1.5VS_VGA)
- The thermal compound on the CPU and VGA was viscus and "stretchy" which made me wonder if it had been applied without removing the previous compound, sometime in the past.

What I have tried:

- Cleaning the RAM contacts with isopropyl, reseating and tried known, working RAM stick.
- Connected an external display(tried HDMI and VGA), both with and without the device LCD plugged into the board. No output.
- Resetting the CMOS, by removing the battery for several hours.


Finally:
I have limited experience with component-level repair and diagnosis, so I apologize in advance for any redundant information or anything crucial I have not done/left off. Any help would be appreciated.

Link to schematic:
https://www.badcaps.net/forum/attach...7&d=1589197578

Link to boardview:
https://www.badcaps.net/forum/showth...hlight=NM-A751 (2nd post down)

Thanks,

Mike

[mon2]

Re: Lenovo 510-15isk - No display & restarting

Confirm the voltage rails on sheets 54, 55, 57 are present.

[Flewmp]

Re: Lenovo 510-15isk - No display & restarting

Thanks for the reply. I have checked, and they are all present.

[Sametbey]

Re: Lenovo 510-15isk - No display & restarting

If the display does not display despite the 3 mainboard changes, the panel may be problematic. have you tried ? On some motherboards, it may not post when it cannot connect with the panel.

[Flewmp]

Re: Lenovo 510-15isk - No display & restarting

If the display does not display despite the 3 mainboard changes, the panel may be problematic. have you tried? On some motherboards, it may not post when it cannot connect with the panel.

Thanks for the reply. I found the idea of changing a motherboard three times strange, but I can only relay what was described to me. I have not tried to connect a different panel, as I do not have any laptop LCDs; is there a way to test the display without the motherboard? I imagine I could inject voltage on the relevant contacts for the monitor cable, but would it show "signs of life" without signals on the other pins? I also recall that the LCD connector (JEDP1) had both the 20V and 3V pins showing the correct voltage. A further update: after clearing the CMOS once again, things remain largely the same; however, I can now hear the hard drive spinning before the device restarts.

[Flewmp]

Re: Lenovo 510-15isk - No display & restarting

Thanks for the reply. I found the idea of changing a motherboard three times strange, but I can only relay what was described to me. I have not tried to connect a different panel, as I do not have any laptop LCDs; is there a way to test the display without the motherboard? I imagine I could inject voltage on the relevant contacts for the monitor cable, but would it show "signs of life" without signals on the other pins? I also recall that the LCD connector (JEDP1) had both the 20V and 3V pins showing the correct voltage. A further update: after clearing the CMOS once again, things remain largely the same; however, I can now hear the hard drive spinning before the device restarts.

Disregard this question, further investigation, as well as this forum post: https://www.badcaps.net/forum/showthread.php?t=80477 would suggest the only surefire way to test would be with a known working, compatible panel.