I noticed that Sector 1 on the East side has had some strange behavior (way too many details are at: drupal.star.bnl.gov/STAR/blog/rjreed/results-2021-epd-install) and it was not entirely clear whether it was the result of a poor optical connection, an electronics issue, damage to the fiber bundle or scintillator.

The piece of evidence is that the bias settings to get a signal out are higher than the other channels, especially on the odd side.

Figure 1: Bias voltage settings 2/24/2021.  Some slight adjustments have been made to a few tiles based on results but is otherwise the same.

First - the dark current didn't change between Run 20 and Run 21:

Figure 2: Dark current tile by tile for the east side.  Note - these were all done at the light leak bias voltage.

Figure 3: Bias scan for the first 3 tiles of East PP1 from 2021.  Even at 61V there isn't much signal.

In addition to the weak signal on the first 3 tiles, tile 5 also has a strange look:

Figure 4: East tile 5.  Not only does sector 1 look weak, but the shape of the spectrum is strange.

Looking at the Bias Scan from 2020 (full giant pdf is at: drupal.star.bnl.gov/STAR/system/files/BiasScan_2020.pdf )

Figure 5: Bias scan of these 3 tiles from 2020.  It looks much better here.

Figure 6: Bias voltages 2021 vs 2020.

In Figure 6 I reran the code so that I was comparing apples to apples (I think 2020 might have had a different ADC value to be aimed for).  Other than 2 tiles, all channels wanted to be at a higher bias setting.