mA Generation
Failure Possible Cause Remedy
Wrong
filament
selection
Filament voltage and
current will be wrong.
Disconnection of
FIL_SELECT or
24V_INTERLOCK lines,
bad transistor on Filament
Driver PCB.
No mitigation on the Generator Driver PCB. The signal passes through to the
Filament Driver PCB. Absence of this signal usually results in a safe condition, as
the filament selection relay is in the relaxed position, selecting the small filament.
Software monitors the SM_FIL_ACK* line before attempting to drive the generator
at a technique only available with the large filament. ABS also adjusts the
technique to the correct level in most cases.
Filament
supply voltage
wrong
Wrong filament voltage,
inability to produce correct
filament voltage. Bad
filament supply regulator,
filament voltage sense
divider or sensor, wrong
filament selected, wrong
duty ratio of drive pulses.
If there is a small error, software on the X-Ray Controller determines the filament
pulse duty ratio needed to compensate for it, before making X-rays. A gross error
indicates a malfunction in the filament supply regulator, part of which is on the
Filament Driver PCB. An apparent error could also be caused by a fault in the
divider feeding the FIL_B_SN_DIV signal to this PCB. The FIL_B_SEN voltage is
monitored at the X-Ray Controller PCB to verify that regulation is working, as set
up by FIL_B_CNTL and FIL_ERROR. This is done before generating X-rays. If
the filament supply voltage is high, there could be a fault in the output stage on
the Filament Driver PCB, but software may be able to provide a temporary work
around of this problem by varying the duty ratio accordingly.
Wrong mA
during shot
Improper exposure (too
high or too low). Patient
dose rate wrong. Incorrect
filament selected. Faulty
mA sense circuit. Tube
aging. kVp wrong.
Automatic brightness control (ABS) will adjust kVp and mA to match the desired
shot, if the filament regulator is working. Software verifies correct kVp by use of
FLUX_SEN. If the wrong filament is selected, it may still be possible to get a
usable picture. Effect on patient dose will be at least partially mitigated by use of
ABS. If the filament regulator has a gross failure, software can still determine the
actual mA and kVp and use the SHUTDOWN signal to disable X-ray production.
If there is a fault in either of the two mA sensors, crosschecking between them
can be verified in software at low (fluoro) levels. If the MA_HIGH* line goes low
when the mA is supposed to be under 14mA, it may indicate a fault in one of the
mA sensors. If the kVp sensor has failed, the FLUX_SEN line provides a check
on the actual kVp delivered to the tube, independent of the tank voltage dividers.
With all of these factors, software will determine whether there is a safety issue
and issue a warning or operate the SHUTDOWN line accordingly.
12
Service
Periodic Maintenance
Contents
Schematics
Illustrated Parts
Installation
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