  PALM-3000 (P3K), the second generation adaptive optics (AO) instrument for
the 5.1 meter Hale telescope at Palomar Observatory, was released as a facility
class instrument in October 2011 and has since been used on-sky for over 600
nights as a workhorse science instrument and testbed for coronagraph and
detector development. In late 2019 P3K underwent a significant upgrade to its
wavefront sensor (WFS) arm and real-time control (RTC) system to reinforce its
position as a state-of-the-art AO facility and extend its faint-end capability
for high-resolution imaging and precision radial velocity follow-up of Kepler
and TESS targets. The main features of this upgrade include an EM-CCD WFS
camera capable of 3.5 kHz framerates, and an advanced Digital signal Processor
(DSP) based RTC system to replace the aging GPU based system. Similar to the
pre-upgrade system, the Shack-Hartmann wavefront sensor supports multiple pupil
sampling modes using a motorized lenslet stage. The default sampling mode with
64x64 subapertures has been re-commissioned on-sky in late 2019, with a
successful return to science observations in November 2019. In 64x mode the
upgraded system is already achieving K-band Strehl ratios up to 85% on sky and
can lock on natural guide stars as faint as mV=16. A 16x16 subaperture mode is
scheduled for on-sky commissioning in Fall 2020 and will extend the system's
faint limit even further. Here we present the design and on-sky
re-commissioning results of the upgraded system, dubbed P3K-II.
