HV Connections for SP HV RETURN Dummy Pad Backplane Connection Do we need to connect the HV and HV return to the “left hand” hybrid? The HV trace serves no obvious function, and the return trace is one of many parallel paths. What happens if these bonds are removed? First test – makes very little difference (over) – seems these bonds do nothing DCAC

Stavelet 5A , 150V bias, bias bonds to H4 removed 2 DEAD CHIP  SWAPPED DCDC ACAC ACAC DCDC ACAC DCDC ACAC DCDC LIN F 150V

“0V” Referencing Paths 1.The Strip Bias line on the detector 2.The HV bias return line on the bus tape (if connected) 3.The Shield Of these three paths, the shield has the lowest impedance (certainly resistance). It’s not really a shield, it’s the dominant return path! If we provide an alternate low impedance path, we may be able to connect the shield at one point only. Module performance may improve.  Try a wire between the PPB board connectors First test – very slight improvement? Inconclusive…

Stavelet 5A , 150V bias, bias bonds to H4 removed 4 DEAD CHIP  SWAPPED DCDC ACAC ACAC DCDC ACAC DCDC ACAC DCDC LIN F 150V

Thoughts and Open Questions Investigating possibility to add bondable strip between hybrids of each module to give a better referencing tie Addition of R in return side of HV filter Change AC/DC order of first module on the stavelet Do we need to revise the HV routing on future bus tapes? Do we need to provide a low resistance referencing tie independent of the shield?