System has not completed prechargecycle, sensed by Analog Interface PCB from +200V (B+) on Generator Driver PCB. Refer to Interlocks/Stator section. After detecting the interlock is complete during the boot sequence, The Technique Processor PCB initiates the pre-charge circuit. The pre-charge capacitors C2 & C3 are charged to the B+ voltage, (approximately 221 VDC). The pre-charge capacitors C2 & C3, located in the Generator Controller Assembly, provide a buffer between the kV/mA regulation circuits and the batteries/battery charger.
The Technique Processor commands the PIO U38-18, on the Analog Interface PCB, togo high after detecting an approximate charge of 185 VDC across the pre-charge
capacitors C2 & C3. (See PRE-CHARGE VOLTAGE SENSING for a description of how the Technique Processor PCB senses the voltage across the pre-charge capacitors). This high passes through buffer U45 pins 17 & 3, turning on transistor Q5 which places a low on the signal CONTACT.
The CONTACT signal passes through the Motherboard and X-ray Regulator PCB,
energizing Relay K2 located in the Generator Controller Assembly. This allows the
continued charging of pre-charge capacitors C2 & C3 directly from the batteries and
battery charger through relay K2 contacts 5 & 6, bypassing current limiting resistor R1.
PRE-CHARGE VOLTAGE SENSING
The voltage across the pre-charge capacitors C2 & C3 is applied through fuse F3 on the Generator Driver PCB to the voltage divider R10/R11. This voltage divider scales the precharge capacitor voltage to approximately 2.5% of the original value. This scaled voltage becomes the +200VSNS signal. The +200VSNS signal is monitored by the Technique Processor PCB through A/D Mux U3-8 on the Analog Interface PCB.
When the Technique Processor detects approximately 4.5 VDC on the +200VSNS line (185 VDC across the pre-charge capacitors C2 & C3) it energizes relay K2 as described previously in the Normal Pre-Charging section.
If the Technique processor never sees the +200VSNS signal reach approximately 4.5 VDC during the boot sequence, a pre-charge error is detected.
(See Pre-Charge Error)
The message PRE-CHARGE FAIL will be displayed on the Control Panel display if the Technique Processor PCB does not see the +200VSNS signal reach approximately 4.5 VDC during the boot sequence (Approximately 185 VDC across pre-charge capacitors).
This is a fatal error that prevents the system boot from completing.
When the system is powered off or the +24 interlock is lost, relay K1 is deactivated. This places resistor R1 between the positive and negative sides of pre-charge capacitors C2 &C3 through relay K1 contacts 3 & 9. Resistor R1 discharges the capacitors.