On the back side of 1Y2 rack I found a cable, CAB-1X2-LSC_7, which is supposed to be connected to the whitening filter was disconnected.

I plugged it back and confirmed that the whitening filter is under control of EPICS.

Now all the gain sliders seem to be working because I can change the amplitude of signals with the sliders.

(method)

  To check if the gain sliders are working or not, I intentionally disconnected all the inputs to the whitening filter.

Then I brought a gain slider of interest to the maximum. Due to the big gain I was easily able to see noise lying above ADC noise.

Also if the gain slider is 0 dB, which is the minimum value, the spectrum becomes just ADC noise.

In this way I checked all the gain sliders from PD1 to PD4. The picture below is just an example screenshot when I was doing this test.

Note that each filer is designed to have two poles at 150 Hz and two zeros at 15 Hz.