9600 Service Manual - gmecorp-usa.com

mA Generation 5
MA DRIVE AND FILAMENT PRE-HEAT
Generates the filament current needed for filament pre-heating and initial tube current.
When a specific mA technique is selected, the system software commands the Analog
Interface PCB to generate the FILDRVA and FILDRVB signals out of PAL U17
(pins 14 & 15) with a duty cycle that the software determines will produce the selected
mA. This occurs immediately in the Fluoro mode. In the Film mode this occurs in the two
seconds prior to an exposure after the X-ray switch is pressed. The duty cycle of the
drive signals, once selected by the software, remains constant throughout the exposure.
These drive signals are then applied to the filament drive PAL U10 (pins 5 and 6) on the
X-ray Regulator PCB. The filament drive PAL U10 then generates its own FILDRA and
FILDRB signals on pins 12 and 13 with the duty cycle commanded by the Analog
Interface PCB.
FILDRA and FILDRB (TP3 and TP2-Generator Driver PCB) drive transformer T2 which
in turn drives the filament drive transistors Q3 and Q4, chopping the regulated filament
voltage (See Table 1) across these transistors. This chopped filament regulator voltage
is transferred to the proper filament transformer in the tank via filament select relay K1.
The amount of filament pre-heat and the initial tube current are determined by the ontime
of these filament drive transistors which are controlled by the duty cycle of the
FILDRA and FILDRB signals. This is the initial setup of the mA loop known as coarse
tuning.
FILAMENT SELECTION
The small 0.3 mm filament is always selected in the fluoro mode and at film mode
techniques of 100 mAs and lower. Software selects the large .6 mm filament when film
mode techniques of greater than 100 mAs are selected.
Filament selection is controlled by the 1 mm MODE signal from the filament drive PAL
U10-14 on the X-ray Regulator PCB. The 1 mm MODE signal controls the filament
select relay K1, on the X-ray Regulator PCB, through transistor Q11.