End Y PLL Open Loop TF results:

Servo Board Settings:

• Input 1 pol: NEG
• Input 1 gain: 0dB
• Common Comp: ON
• Common Generic Filter: ON
• Fast gain: -8dB
• Fast option: ON
• Fast pol: POS
• rest off/zero

The UGF is at 23kHz with a phase margin of 52 deg (consistent with HIFOX). Using the AG spectrum analyzer, I tried finding the PZT resonance. The data is a bit ratty, but there appears to be a resonance a little below 200kHz (see the picture -- the two pictures were collected with different BWs; the first at 300Hz and the second at 2Hz; this notch-looking feature seemed to be repeatable...).  Meanwhile, the board has a notch at around 280kHz, which also seems to appear in the pictures.

I have also uploaded and plotted the data I collected.