We have used channel 17-20 of the lower AA chassis, which was originally PR p/y/s and BS p. The four signals from four segments of KAGRA QPD are using them. 

A marix was designed to convert them into p/y/s. And then it is connected to BS block.

Accordingly, channel 21 and 22 were changed to be connected to PR block (as in the attached figure).

The whole modification is shown in the attached figure, will be changed back after QPD test.