AMD Athlon II P340 to Phenom II N640 upgrade

[beobi]

I am trying to upgrade HP laptop cpu from P340 to N640, but machine fails to boot and no post. Is the voltage for these chips different.
All motherboard, power supply, heatsink part numbers, bios version appear correct. CPU tested good by supplier.
Only thing I can think is voltage setting, but no way to adjust in bios.

Thanks