# Follow-up of the PD1 vs PD2 swap for PSTAB
After the PDs swap of yesterday (46393) we observed 2 periods of glitches on the channel PD1_AC (which refer now to the photodiode PD2). See plot 1 & 2 (legend), look at the plot at the ordinates +1 and -3 (glitch number on PD1)
plots 3/4/5 refer to some of those glitches.
we notice that only the channels PD1_AC is affected, nothing visible on PD2_AC as usual, but also nothing visible on IMC_TRA nor on the PSTAB associated quadrant (see plot 5).
This means that, as suspected, one single path is spoily (the one from the photodiode PD2 up to its connection into the EERoom). This path is now the Outof Loop PSTAB path which is only a monitor path.
The issue now is that OoL path in its current state cannot be considered as a spare path for PSTAB
# Next
- We need for a systematic analysis of the PSTAB glitches to state that this subject is over.
- we need to understand from where comes the glitches. One guess is some mal-functionning of the photodiode PD2 itself.
- One action is to reduce the power impinging on the PDs (1.3V/50ohm = 26 mA up to now). We could afford this since PSTAB floor is far from being the limitation of the Virgo sensitivity. This would just proove that the issue come at the PD level rather than on cabling of drivers
- we can try to swap the cables fron INJ flange to EERoom to exonerate the photodiodes & driver
