mA Generation
mA Generation
Failure Possible Cause Remedy
Filament drive
pulses absent
With either filament drive
pulse absent, the Filament
Driver PCB produces no
drive and the X-ray tube
cannot produce x-rays. If
only one drive is present,
the filament drive circuitry
does not operate properly.
One FET will be always off,
so no filament drive occurs.
Application of high voltage
to the X-ray tube without
filament drive might cause a
hazard, as the tube cannot
discharge it.
Optoisolators faulty, broken
connections, no
FIL_DRV_RTN connection,
fault in 7407, faulty 74LS14,
fault in FIL_CUR sensor.
A detection circuit on the Generator Driver PCB looks for the presence of filament
current above that in sleep mode. If either or both pulses are missing, there’s no
filament current and the signal FIL_DRV_OK* goes high, indicating this condition
to the X-Ray Controller PCB. The software monitors this signal before enabling X-
ray production. If FIL_DRV_OK* is high, or is disconnected from the card cage,
the HV Supply Regulator disables kVp drive and prevents X-ray production. If
pulses are present at the Generator Driver, but not getting to the Filament Driver
PCB, or if there is a fault on that PCB, absence of a filament voltage at
FIL_VOLT_DIV causes FIL_VOLT to be zero. If there is filament voltage, but no
current, FIL_CUR is zero. These two signals also return to the X-Ray Controller
PCB and are monitored by software to detect incorrect drive voltage and current
for the duty ratio and filament selected. The FIL_DRV_OK* signal is produced by
comparing FIL_CUR on the Generator Driver PCB with a fixed voltage
representing a current higher than that in the sleep mode.
8
Service
Periodic Maintenance
Contents
Schematics
Illustrated Parts
Installation
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