Tim, The ion pump supply should be on if the unit is plugged in and on. Remove the HV connector from the supply to remove any load and measure the divided test point on the bottom of the chassis. It should read between 2.45 and 3.0 VDC, if not measure from pin 4 of the ion pump supply to ground. You should have 19VDC. If HV is good with connector removed and bad with it on, the ion pump is most likely shorted. If the 19VDC is bad then the regulator between the +50VDC and the ion pump module is bad. Depends if you have an option 10 or not how it's hooked up but you should be able to trace it. Corby ____________________________________________________________ Click here to compare rates and find the best deal on renting a car. http://thirdpartyoffers.juno.com/TGL2141/fc/Ioyw6i3nMUn1OOMQpmC43JlqxKWoQZXE64rYNrKeVdmeTS0S431emt/