Chamber side testing of the PSAMS shows that the Strain Gauge (SG) voltage of ZM5 has railed at -28V (which indicates an open circuit.). I am able to drive and measure the PZT voltage from 0 to 200V, however the strain gauge voltage always remains at -28V (strangely the SG resistance still shows the correct 700ohms and 360 ohms values) - so I am not sure how, but perhaps there is some loose connection.

To further confirm this - I tested ZM4 (which shares the chassis with ZM5) and I was able to drive the PZT voltage from 0-200V and correspondingly get SG voltage of 3.5 - 7.7V (which ties up with my previous measurements in performed 2023). To rule out an issue in ZM5 electronics chain I hooked up ZM5 to the healthy electronics chain of ZM4 and repeated the above measurement and still obtained an open circuit for ZM5.

Hence, ZM5 PSAMS is broken and needs immediate replacement. Work to replace PSAMS is currently ongoing.