Lenovo Legion Y7000P 2019 1660Ti Repair Notes

Laptop Model: Lenovo Legion Y7000P 2019 with a 1660 Ti graphics card.

Problem

The graphics card wasn’t being detected after power-on. Even with power to the GPU and VRAM, it wouldn’t show up. Sometimes it would appear briefly after driver installation, then disappear.

Troubleshooting Process

  1. Initial Steps
    • I confirmed power was present at the GPU and VRAM.
    • Based on experience, I reballed both the GPU and VRAM. The issue persisted.
  2. Deeper Diagnosis
    • I decided to check the GPU’s working conditions.
    • I found that the PEX_RST# signal, which comes from the PCH (Platform Controller Hub, or Southbridge), was inconsistent.
    • I applied heat to the PCH, and the GPU was detected. It could even run 3DMark for a while before the system would crash with a bluescreen.
    • Conclusion: The PCH had a cold solder joint.
  3. PCH Replacement/Repair
    • I reballed and reinstalled the PCH.
    • Result: The GPU issue was resolved; 3DMark ran perfectly.
    • New Problem: The keyboard and touchpad stopped working.
  4. Keyboard/Touchpad Troubleshooting
    • I suspected I might have soldered the PCH incorrectly or that the chip itself was now bad.
    • I reballed and reinstalled the PCH a second time, but the problem remained.
    • I then shifted my focus to the keyboard’s working conditions.
    • Finding: The keyboard controller chip, IT8176FN-56A, had no power.

      IT8176FN-56A
      IT8176FN-56A
  5. Power Supply Investigation
    • The keyboard chip’s power comes from the SY6288D20AAC converter chip.
    • I checked the conditions for the SY6288D20AAC and found that its enable signal, AGKB_PWR_EN#, was missing.
    • I traced the signal back and found it’s controlled by the EC (Embedded Controller).
    • Analysis:
        • My immediate thought was that the EC was faulty, or perhaps the PCH wasn’t sending a necessary signal to the EC, which in turn prevented it from outputting AGKB_PWR_EN#.
        • I also noted that this signal is tied to both PCH_PWR_EN and RGB_PWR_EN.
        • On this specific motherboard, the resistor for RGB_PWR_EN was open, meaning AGKB_PWR_EN# was only connected to PCH_PWR_EN.
        • After reviewing the schematic, I saw that the SY6288D20AAC chip isn’t strictly necessary on this board, and its power could be supplied directly from 3VALW.

  6. The Solution
    • The Fix: I decided to try a direct power connection.
    • Action: I removed the SY6288D20AAC chip and soldered a 0-ohm resistor from a donor board to connect 3VALW directly to the keyboard chip’s power pin.
    • Result: The keyboard and touchpad are now working.

Conclusion & Discussion

  • My belief: The keyboard and touchpad issue is a direct result of the PCH repair. While the PCH fix resolved the GPU problem, it likely failed to output a signal (like PCH_PWR_EN) that the EC needs to enable power to the keyboard controller.
  • Alternative possibility: The SY6288D20AAC converter chip itself could have failed and was pulling the AGKB_PWR_EN# signal low.
  • Current Status: The laptop is fully assembled and working. I’m not going to take it apart again. This post is to share my experience and ask if others have seen a PCH replacement cause keyboard/touchpad issues. The direct power bypass worked, and I’ll keep an eye on any future problems.