More than often, some keys don't function, always the same: 1 6 a d s g j... When this problem occurs I can type using a second key as shift or space bar.
To be honest it’s not known to me that the L550 would be affected by the same keyboard issue as the L670.
Did you test this notebook behavior using an external USB keyboard?
Do that…
If the same issue would not be available using the second external USB keyboard, then this means that the BIOS is ok and the internal keyboard is affected.