The  ion pump that pumps GV12's annulus volume seems to have shorted out a few hours after valving-out the turbo setup last Friday.  So today, I valved the turbo back in and let it "assist" the ion pump but the ion current never came on scale.  The pressure gauge at the aux. cart  indicates that the annulus volume is at a low enough pressure that the ion pump should easily be able to handle the gas load.  I swapped the controllers and tapped the pump body - no help.  I next connected a high power / high voltage DC power supply to the pump in place of the nominal low power controller but couldn't increase the voltage above 40 volts which indicates a "robust" short. 

For tonight, I am leaving the ion pump off and the turbo valved-out.  It looks like we may have to vent the annulus volume and replace the ion pump tomorrow.  This is "undesirable" as the gate annulus volume (now believed to be exposed to the beam tube vacuum) will be separated from the adjacent vented annulus volume by only (1) metal-sealed valve during the replacement process.  We prefer to always have two layers of protection between atmosphere and the BT.