Looked at cabling coming from Red QPD (chamber) to QPD Transimpedance Amplifier Chassis D1002481(rack). Used voltmeter to do a diode measurement across QPD1 (four segments) and QPD2 (four segments). Was expecting to see around 0.6V for the forward voltage drop across the diodes. Did not see any voltage drop on cable ISC-BSC6-1. Performed test on cable ISC-BSC6-2 (green QPD) and saw the expected 0.6V across the diodes. Next we swapped ISC-BSC6-1 and ISC-BSC6-2 at the chamber vacuum feedthru. Retested at rack side, and cable 1 tested good, cable 2 did not pass. We had also noticed 
cable 1 had a short from Pin 13 (GND) and Pin 16. Reverified at chamber side.