Yoga3 Pro-1370 Board NM-A321 DEAD no power at all

[k370]

Hi everyone,

I have a NM-A321 board that is dead, with no power at all.

When I received the laptop, the +5VPMIC line was shorted. Removing the PU3 (ISL95905) solved the short, so I ordered and replaced the ISL.

With the new ISL, the short is gone, but still no voltages at all. I measured the following rails:

• +3VALW
• +5VAUX
• 1.2VSUS_PWRGD
• 3VALW_PGD
• 1.05VAUX_PWRGD

Additionally, the ISL95906 (PU3) is not getting any voltage on the VIN rail.

The only place on the board where I find any voltage is on the first MOSFETs, specifically:

• PQ5
• PQ6
• PQ15
• PQ16

These are driven by PU4 (BQ24770), but this IC is also not getting any voltage at all. As pointed out by another member in a related post about this board, there's no point in changing this IC until we have 3VALW. Here's the link to the post: https://www.badcaps.net/forum/troubl...-board-nm-a321

I've already measured all the MOSFETs and checked for other shorts; everything seems fine.

Any tips would be welcome!

I'll also leave the board view and schematics I'm using.
Note: PJ7 +5VDX_WALKPORT, which provides power to the USB ports, has very low impedance (20 ohms). I've lifted the pad for troubleshooting and believe that this rail doesn't impact the board turning on and showing an image. I'll worry about this later after I get the board to boot.

https://www.badcaps.net/forum/troubl...0-lcfc-nm-a321

[reformatt]

CHGVCC voltage? ACDET? Does laptop run off a charged battery? You can also do a Sorin hack, and apply external power supply to battery terminal (around the same voltage as the battery as it's a NVDC charger) and see if the laptop comes on.

[k370]

CHGVCC voltage? ACDET? Does laptop run off a charged battery? You can also do a Sorin hack, and apply external power supply to battery terminal (around the same voltage as the battery as it's a NVDC charger) and see if the laptop comes on.

Thank you for the tip.

I already injected voltage into the battery terminals and got 5V, 3.3V, and the battery LED blinking when the power button is pressed, indicating a low battery, but it still won't power on.

Based on this test, I'm inclined to order and replace the PU4 (BQ24770).

What do you think? Should I measure something else?

[reformatt]

You could order it, but some basic measurements around the IC would help.

[k370]

You could order it, but some basic measurements around the IC would help.

es, you're right, taking measurements instead of relying on assumptions is always better.

Measurements on charger (without battery):

• Pin 1: 0.18V
• Pin 2: 0.18V
• Pin 3: 0.17V
• Pin 9: 0.02V
• Pin 14: 0.20 to 0.40V (fluctuates)
• Pin 27: 0.02V

Measurements on battery and charger (battery voltage at the time of measurement: 6.77V, rated battery voltage: 7.6V):

• Pin 1: 6.40V
• Pin 2: 6.40V
• Pin 3: 0.93V
• Pin 4: 0.93V
• Pin 11: 3.30V
• Pin 12: 3.30V
• Pin 15: 0.28V
• Pin 17: 6.17V
• Pin 19: 0.63V
• Pin 20: 6.77V
• Pin 25: 6.52V
• Pin 26: 6.66V
• Pin 27: 6.77V
• Pin 28: 6.61V

I also leave a picture of the BQ24770 pinout for easier reference and analysis.

[reformatt]

With charger connected, I would expect Pin 28 to be 19V via PD2. As it's only 6.6V, then this is only being fed from the battery via PD3. So clearly you have an issue with the adaptor input circuit. For future reference, troubleshooting BQ charger IC's the most basic things for us to check are VCC, ACDET, ACOK and REGEN pins, which you have omitted above. But these are irrelevant right now.

There is a fuse PF2, followed by two P channel FET's PQ10/PQ11. These will be under the control of PQ14A, controlled by USB_ID from the Lenovo charger. I'm assuming this is a voltage, rather than forming part of a resistor divider (as there doesn't appear to be any internal pull up etc). Assumption is that USB_ID turns on PQ14A, turning on PQ10/PQ11 and providing your volts to the your BQ IC.

[mon2]

Test the voltage to ground on each pin of PD3 with both, the battery and the power adapter connected. In this case, the power adapter voltage (since it should be higher than the battery voltage) should power the Vcc pin as noted by reformatt.

[k370]

With charger connected, I would expect Pin 28 to be 19V via PD2. As it's only 6.6V, then this is only being fed from the battery via PD3. So clearly you have an issue with the adaptor input circuit. For future reference, troubleshooting BQ charger IC's the most basic things for us to check are VCC, ACDET, ACOK and REGEN pins, which you have omitted above. But these are irrelevant right now.

There is a fuse PF2, followed by two P channel FET's PQ10/PQ11. These will be under the control of PQ14A, controlled by USB_ID from the Lenovo charger. I'm assuming this is a voltage, rather than forming part of a resistor divider (as there doesn't appear to be any internal pull up etc). Assumption is that USB_ID turns on PQ14A, turning on PQ10/PQ11 and providing your volts to the your BQ IC.

Thank you for your help and time. I'm going to investigate further based on your suggestion. I will update my findings later for the reference of other users.

[k370]

reformatt mon2

Following these tips, I was able to identify that PQ14 was damaged. I replaced it with one from another donor board, and now it works just fine. Thank you for your input; without it, the repair probably would not have been successful.

Regarding the short on PJ7 +5VDX_WALKPOR, I found that the problem was the U40 IC, which was shorted, as well as a USB charging control IC (TPS2546) on one of the sub-boards that I have already ordered.