While changing HI degrader foil to 10um Al, the E detector was investigated, due to previously observed alpha punch-through.
On visual inspection, the E detector appeared to be 1mm in thickness, leading us to believe that instead we were not fully depleting the detector.

The bias supply was investigated, and was found to be supplying a lower voltage (on all channels) than was shown on the display (14V -> 2V in reality, 350V -> 60V in reality).
The bias module was replaced, and the faulty module marked as such.

As a result of this change, the configuration of the detector bias channels has been altered (as ch 2 on new module can't supply >100V).

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New Configuration:

Detector    :  Voltage :  Leakage Current
Ch 1 -  dE :    40 V    :        0.92 uA
Ch 2 -   HI :    14 V    :        2.52 uA
Ch 3 -    E :   350 V   :        3.91 uA