The right choice of the BIOS version

Performance limits introduced by the newer versions of BIOS

From the release of this model to the latest version of BIOS (JYCN50WW, which has been removed from the official website), Lenovo has been sparing no effort to do two things:

• Increasing the amount of bugs in the ACPI table
• Reducing the power limit of the laptop to cut down the return rate

Among them, reducing the power limit of the laptop is particularly contemptible, cases are:

• Starting from version JYCN37WW, the performance mode can not be applied when the laptop is charging with the legion 135W PD charger, which makes the advertising Lenovo made on it a joke.
• Starting from JYCN49WW, the CPU power limit of the laptop is unbelievably strict when the AC adapter is not connected: the CPU frequency would be limited to 800MHz max. This kind of limiting is so ridiculous that it can hardly be explained by intention to enhance the battery life.

Recommended BIOS version

JYCN34WW is recommended with it's characteristics being:

• When AC adapter is plugged in the power limits are: 90W PL1 and 140W PL2 under performance mode, 60W PL1 and 70W PL2 under balanced mode, 25W PL1 and 45W PL2(with short duration) under quiet mode.

• Without AC adapter plugged in the performance mode is disabled and the power limits are: 25W PL1 and 45W PL2(with short duration) under balanced mode, 25W PL1 and 45W PL2(with short duration) under quiet mode.

• The total power draw is limited at 160W with no known way to override.

• This version of the BIOS did not implement the cross-loading power limit adjusting. However a total power draw of 160W (100W GPU plus 60W CPU) is quite satisfying already.

• The BIOS has some problem handling USB HID devices in that when connected with external keyboards/mice, grub might freeze. When this happens all external keyboards/mice need to be removed in order to fix it. It is known that the later version of BIOS did not fix this problem.

Note that Lenovo has already removed the download links for most of the earlier versions of the BIOS. You could download them from this link (I am not particularly sure if these BIOS images can be used for international versions of the laptop so do with your own risk)

Before updating/downgrading your BIOS

• Please note that downgrading(aka backflashing) the BIOS is only possible when the 'BIOS backflash' option is turned on in the BIOS settings.
• Please note that downgrading the BIOS would reset the tpm device. And this could (with high chance) cause you trouble logging into Windows.
• Please make sure that the bitlocker encryption is disabled in Windows before downgrading.
• Please reset all the BIOS settings before downgrading to avoid your laptop getting bricked.
• Please turn the performance mode to balanced before doing any BIOS updating/downgrading! THIS IS VERY CRUCIAL SINCE IT IS KNOWN THAT UPDATING/DOWNGRADING THE BIOS UNDER CUSTOM MODE IS VERY VERY VERY LIKELY TO BRICK YOUR LAPTOP!