Measured both the filtered and DC output of the power stabilisation photodiode, a measurement
that was limited at low frequencies by the noise of the SR785 (S/N 77457), which seemed to be
somewhat higher than normal.  The broad peak at ~45 kHz present is not present in the bias
voltage, nor the power supply voltages.  The photodiode showed no visible signs of damage.  As
a result I was reluctant to remove it from the circuit, plus it had the glass window taken off
which makes it even more prone to damage if one was negligent.  The filtered noise is consistent
with the gain of 400 from the DC output.

  PDTF2.png shows the measured transfer function from the test point TFIN out to the test point
X5 and the filtered output.  Both are as they should be.

  Removed some extraneous flux from both sides of the circuit board, re-assembled the photodiode
box and then re-installed it on the table.  The sample output of the pre-modecleaner was aligned
onto the photodiodes by peaking the DC output.  The beam onto the internal quadrant photodiode
was then re-positioned to zero the X and Y outputs as best as possible.

  The alignment into the pre-modecleaner was tweaked to try and minimize the free-running
peak-to-peak fluctuations.  The power incident on the photodiodes was adjusted so that the
filtered output was not saturated.  This seemed to be with a DC output of ~7.5V.  Then power
stabilisation was then engaged.  Further alignment tweaks for the pre-modecleaner are probably
warranted.



Jason, Peter