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!

 

[ThienBui]

I don't understand where you get so much information

 

[wakoypangan123]

I don't understand where you get so much information

I’ve been researching the problem quite extensively because I really want to understand what happened to my laptop and find a way to recover it. I’ve been reading about Lenovo BIOS modding, Intel memory initialization, DDR5 training, NVRAM, SPI firmware, and SPD hubs, and I’ve also been getting information from different forums and technical discussions.

I’m not an expert in all of these areas, so some of the information may not be completely accurate. That’s actually why I posted the question—to get help from people who have more experience with these platforms and can correct me or point me in the right direction.

 

[ThienBui]

Instead, use the elimination method, it will be faster, you know we are technicians that need to solve problems quickly, not training...

 

[wakoypangan123]

I don't understand where you get so much information

To make it simple, I tried flashing the BIOS from Lenovo, and now the laptop has these 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 every 15 seconds
• It never reaches normal POST

I've already asked for help on Win-Raid and followed the advice there, including creating and flashing an SPI image, but the laptop still does not boot. https://winraid.level1techs.com/t/p...rx-spi-image-creation/116078?u=wakoypangan123

I'm just trying to figure out what went wrong and whether the BIOS can be properly recovered.