A customer recently started getting mA & kV faults on their Gendex ATC725 generator when ever they took an x-ray higher than 75 kV. After doing all the usual checks for tube arcing, high tension cable checks, etc. we looked at the DC rail voltage. It was correct at 390 Vdc but after further monitoring we discovered two things were happening to the voltage level. While monitoring the rail during an exposure it would drop drastically low to less than 200 Vdc. We also monitored the rail when we turned the generator off. Usually this voltage will bleed off slowly but in this situation it dropped to 0 Vdc in a matter of seconds after being turned off. We also monitored the incoming line voltage which was solid until we measured it across the line contactor. The line voltage would drop about 50 Vac across the contactor during an exposure. It turns out we had 2 problems of which both would cause mA & kV faults. We found 3 bad high voltage capacitors on the rail which would contribute to the rail voltage dropping during exposures and after the unit was turned off, and we also found defective contacts on the line contactor which accounts for the line voltage drop across the contactor. Fortunately the technician investigated the rail voltage and the line voltage before ordering any parts. If he would have stopped troubleshooting after finding the bad caps he would have had to order more parts and made a return trip after finding the bad contactor when he continued to get mA & kV faults. Check the rail voltage and line voltage when trouble shooting generator faults.