Chapter 4 Theory of Operation
Revision W HF Series X-ray Generators - Service Manual
4-14 Quantum Medical Imaging
HSS Control Board A20A1 (AY40-035S)
The HSS Control Board A20A1 receives operating handshake commands
(such as SYSTEM ON/OFF) from the generator Logic Board A1 (AY40-004S)
through connector J2. The signals coming and going to the Logic board via J2
are optically isolated. The handshake signals control the high speed starter’s
Rotor On, Boost, Run and Brake sequence. The Boost and brake time settings
are based of the tube model selected for the generator.
CAUTION! It is important that the proper tube is
selected otherwise damage may be caused to the
tube rotor due to incorrect Boost and/or Brake
timing.
Oscillator A20A1U11 generates a 36 kHz square wave output, which is then
divided by counters to create 180 Hz (High Speed) and 60 Hz (Low Speed)
reference frequencies required to synchronize all control events.
The 60 Hz and 180 Hz drive outputs each consisting of two, 180° out-of-
phase signals, DRIVE 1 and DRIVE 2 (available for monitoring at A20A2TP5,
A20A2TP6). These outputs are buffered and then sent as drive signals to
IGBTs on HSS Drive Board A20A2. Under the control of the generator Logic
Board A1 and HSS Control Board A20A1, relays on the HSS Drive Board out-
put a sequence of AC voltages (High/Low Speed Boost and Run) to the x-ray
tube based on the tube type configured in the generator. Redundant hard-
ware protection is provided to limit maximum Boost and Run times.
For High Speed (180 Hz) operation, following the end of the Run phase, a
Brake phase is initiated. During this phase, one output phase is On while the
other is Off. The DC braking voltage is generated through rectification of the
Run AC voltage. The duration of the Brake phase is dependent on the tube
type selected.
The high speed starter voltage and current on HSS Drive Board A20A2 are
monitored continually by circuits on HSS Control Board A20A1. If an over-
voltage or over-current condition occurs, the HSS Control Board terminates
operation of the high speed starter. Test point A20A1TP10 provides the indi-
cation of over-voltage or over-current (i.e., TTL-low signal indicates FAULT
condition).
The HSS Control Board A20A1 also monitors whether or not the tube is rotat-
ing (ROTATING signal at A20A1TP19), and whether it is rotating at High
Speed 180 Hz or Low Speed 60 Hz (HIGH/LOW SPEED signal at A20A1TP8).
If the ROTATING signal at A20A1TP19 is not logic low during operation of the
high speed rotor, a "Not Rotating" error appears on the Operator Control
Panel display.
The available test points on HSS Control Board A20A1 are:
•TP1: GND
• TP2: +15V
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