Ask Lenovo ThinkBook 16p G5 IRX – No POST After Changing JEDEC Write Leveling in Advanced BIOS

[wakoypangan123]

Hi everyone,

I need help recovering my Lenovo ThinkBook 16p G5 IRX (LB650 / NM-F891, FRU 5B21N94928).

Here is what happened:

• The laptop was originally running P5CN29WW BIOS.
• I successfully downgraded it to P5CN28WW.
• The laptop continued to boot and work normally after the downgrade.
• I used the Lenovo Legion Advanced BIOS method to unlock the hidden/advanced BIOS menu.
• I successfully undervolted the CPU through the advanced BIOS settings.
• The laptop was still working normally after the BIOS unlock and CPU undervolt.
• I then changed the JEDEC Write Leveling setting in the advanced BIOS.
• After saving the change and rebooting, the laptop stopped POSTing.

Current symptoms:

• Fans spin.
• Keyboard backlight turns on.
• No Lenovo logo.
• No display output.
• Caps Lock/Num Lock do not respond.
• The laptop appears to reboot approximately every 15 seconds.
• It never reaches normal POST.

I believe the problem is directly related to the JEDEC Write Leveling change, because everything was working correctly before I changed that setting.

I have tried/researched BIOS reflashing and recovery, and I have been investigating whether the setting could have been stored in UEFI NVRAM, memory-training data, Intel firmware, or potentially the DDR5 SPD hub NVM.

I also have access to SPI programming equipment and have been working with the firmware chips on the motherboard.

Could anyone with experience with Lenovo/Intel platforms or DDR5 memory training please help me determine:

1. Where is the JEDEC Write Leveling setting likely stored?
2. Could this setting survive a normal BIOS reflash?
3. Could it have modified DDR5 SPD hub NVM?
4. What is the correct way to completely reset the memory-training configuration?
5. Would replacing the DDR5 SO-DIMMs with known-good modules help determine whether the issue is related to SPD/NVM?
6. Is there a specific NVRAM variable or BIOS region I should investigate?
7. What would be the safest recovery procedure for this particular motherboard?

I would really appreciate any advice or guidance from someone experienced with Lenovo BIOS modding, Intel memory initialization, DDR5 training, or SPI firmware recovery.

Thank you!