Calibration
Adjustment of Dead Time Between kV Drive Signals
CAUTION: To prevent cross-conduction in and destruction of the IGBTs, turn both R137 and R84 on the High
Voltage Supply Regulator PCB fully clockwise. This increases the dead time between High Voltage
drive pulses to maximum.
CAUTION: This adjustment sets up the dead time between the kV drives signals on each of the IGBT pairs (Q1
and Q2). Misadjusting the dead time so that both transistors of Q1 or Q2 are on at the same time
damages the transistors.
Note: Variations between Generator Driver PCBs can cause dead time adjustments to vary. Check the dead time adjustment
any time you change the Generator Driver PCB.
1. Turn system off.
2. Connect channel 1 of the oscilloscope to TP67 on the Generator Driver PCB and oscilloscope channel 2 to TP68.
3. Turn system on and allow Workstation and C-Arm to boot completely.
4. Select a technique of 40 kVp @ 0.2 mA.
5. Align the two channels on the oscilloscope so that they have the same reference point, and adjust for about 5 Volts per
division vertical sensitivity.
6. While observing the dead time (the time when both pulses are below the 5 VDC reference), take an X-ray, and adjust R137
on the High Voltage Supply Regulator PCB counterclockwise to achieve a dead time of about 1.5 µsec on the drive
waveforms at the 5 VDC level. Typically one dead time will be longer than the other. Make sure the
smaller
of the two is as
close to 1.5 µsec as possible without getting any lower than that. Refer to the following illustration, which shows the kV drive
signals with the dead time properly adjusted.
11
Service
Periodic Maintenance
Contents
Schematics
Illustrated Parts
Installation
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