5-4 P/N 9-500-0255
Service Manual
Chapter 5: Maintenance—General
Troubleshooting
Communications Interface
The Communications Interface PCB distributes fused low voltage to the system, as
well as being the communications interface between the Host microprocessor and
all sub-systems.
C-arm Safety
The C-arm Safety PCB reads the output of a strain gauge mounted to the vertical
travel assembly (VTA). This output represents the external force applied to the C-arm
in the downward motion, and the circuit is calibrated to inhibit the VTA down motor
drive upon sensing approximately 35 pounds (154 Newtons) of applied pressure.
The inhibit signal is monitored by the Host microprocessor and in turn is
communicated to the Power Control PCB to inhibit the VTA down drive.
Power Control
The Power Control PCB controls the following system functions:
• Collimator lamp power
• Compression motor drive
• Compression motor brake
• Rotation Lock release
• VTA actuator drive
All input signals come from the Host microprocessor PCB.
3.1.4 Tubehead Functions
The tubehead micro-controller (PIC series) communicates with the Host
Microprocessor via the RS-422 I/O port. This PCB receives input to control the
collimator assembly motions (Mirror, Auto-Aperture, Lamp, and Filter movements)
and reports to the Host Microprocessor the status (position) of each movement. The
removable apertures are encoded with a 4 bit word and this information is
communicated to the Host Microprocessor. These functions are all processed by the
Host microprocessor and must match a valid condition before an exposure may be
initiated.
This PCB also supplies drive to the Filter Indicators (Mo and Rh) located on the
external switch panels.
3.1.5 X-ray Tube Control
The x-ray tube control involves the filament, stator drive (boost and brake), and high-
voltage control circuitry. This system is comprised of the Tube Control PCB, the
Inverter PCB, and the high-voltage transformer and multiplier.
Filament Control
Filament power is supplied by a pulse-width-modulated (PWM) inverter supply. The
filament is operated at a stand-by current of approximately 2.5 Amps. Upon
exposure initiation, the filament is boosted to its emission level determined by the
technique selected (pre-heat) and then is transferred to closed loop servo control
during the exposure. The filament High power source is applied to the common of
relay K1 which directs the power to the selected filament (small or large). This
supply is connected to the x-ray tube low voltage connector via the Tube Protect
PCB. The filament current is sensed and used as an input element for the PWM
control.
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