N9030B PXA Signal Analyzer Service Guide 305Power Supply/Midplane TroubleshootingA6 Power Supply Assembly TroubleshootingControl InputsPOWER_ONPOWER_ON is a signal that when pulled low tells the A6 PowerSupply assembly to turn on all of its outputs. This signal comes fromthe A4 Processor board assembly and is initiated by pressing the frontpanel power button.If the instrument will not turn on be sure that this line is being pulledlow by either measuring the voltage level at Test Point 518 on the A7Midplane board assembly or by viewing the status of thePOWER_ON_L LED. See the "A7 Midplane Board AssemblyTroubleshooting" on page 310 for detailed information on thelocation of this test point and LED as well as the expected status forboth when the instrument is operating properly.Status OutputsPOWER_OKThe POWER_OK status output is an indication of whether or not all ofthe digital power supply voltages are up to their specified voltagelevels or not. If all of these supplies are working properly this outputline will be at a TTL high level. If this output is not at a TTL High levelthe instrument CPU will not come out of its reset state and will notboot-up. Once this output goes to a TTL high level the instrumentCPU will start its boot-up process and the POWER_ON_L line comingfrom the A4 Processor assembly will go to a TTL low level which willtell the A6 Power Supply assembly to turn on the rest of it outputvoltages.If the A6 Power Supply assembly is suspected of causing theinstrument to not power on properly the status of this output can beverified by either measuring the voltage level at Test Point 506 on theA7 Midplane board assembly or by viewing the status of thePOWER_OK LED. See the A7 Midplane Board AssemblyTroubleshooting section in this chapter for detailed information onthe location of this test point and LED as well as the expected statusfor both when the instrument is operating properly.FAULT_LThe FAULT_L status output is an indication of whether or not there isa fault detected by the A6 Power Supply that is keeping it frompowering on properly. If all of the required conditions to turn the A6Power Supply assembly on properly are being met this status outputline will be at a TTL high level. The conditions that could cause thisstatus output line to be at a TTL low level include that of an overcurrent condition, an over voltage condition, and an over
