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Chapter 3 Theory of Operation

Models QT-740 & QT-750 - Service Manual

OVERVIEW

Model QT-740 and QT-750 Odyssey HF Series X-ray Generators feature a tabletop that

"floats" in four directions for transverse and longitudinal patient positioning. The tabletop

of Model QT-750 can also be raised and lowered.
The tabletop floats (rides) on 30 bearings; 26 provide longitudinal tabletop motion, and

four are provided for transverse (forward and backward) tabletop motion. The longitudi-

nal bearings are bolted to two precision-machined stainless steel bearing bars, which are

mounted below the tabletop on the front and back sides of the table. Four 1-5/8" load

bearings bolted on the Transverse Carriage Assembly permit transverse travel of the

tabletop. Eight anti-racking and four anti-tipping guide bearings, bolted to the Tranverse

Carriage Assembly, stabilize tabletop transverse motion by controlling movement of the

left and right Transverse Rails.
Two fail-safe brakes (24 VDC electromagnets) are positioned extremely close to the bear-

ing bars. When the electromagnets are de-activated (i.e., FLOAT foot pedal/push button

is not pressed), the fail-safe brakes "grab" the bearing bar securely, locking the longitudi-

nal travel of the table. Similarly, two fail-safe brakes (24 VDC electromagnets) are used to

grab the Transverse Rails, locking the transverse travel of the table. Depressing either the

FLOAT foot pedal(s) or push button energizes the electromagnets, releasing the fail-safe

brakes and allowing the tabletop to float freely both longitudinally and transversely.
The Receptor Cabinet rides on four linear ball-bearings mounted to adjustable brackets

attached to either side of the cabinet. These bearings travel on the hardened and pol-

ished steel shafts of the Receptor Cabinet Carriage. One electromagnet on the underside

of the housing "locks" the Receptor Cabinet into place until the Receptor Cabinet Lock

Release switch is depressed, thereby releasing the magnet's hold and allowing free move-

ment of the Receptor Cabinet.
The following paragraphs provide theory of operation for Model QT-740 and Model QT-

750 Odyssey HF Series X-ray Generators.

MODEL QT-740 TABLE

The table's major electrical components include the AC transformer and fuse block,

printed circuit boards, and magnetic locks. See Figures x and x in Chapter 5, Dia-

grams.

Power Distribution

115/230 VAC line input is applied through fuses F1 and F2 to step-down trans-

former T1. Transformer T1 provides 18 VAC to 4-Way Table Control Board con-

nector A1J1-1 and A1J1-2. The 18 VAC input is applied to full-wave bridge

rectifier A1DB1, filtered by A1C1 and A1C2, and applied through resistor A1R2

and zener diode A1D1 to p12 VDC. The +24 VDC output of A1DB1 is

connected to A1J1-6 to p24 VDC to the bucky, transverse, and longitudi-

nal electromagnets.

Float Control

Model QT-740 tables have one foot pedal and one push button switch (located

below the tabletop on the right transverse assembly cover) that control four-way

NOTE

On 115 VAC
systems, the
power supply
cord is the
power
disconnect
device. On 230
VAC systems,
the power
disconnect
device is either
the generator
circuit breaker
(when
generator is
power source)
or the main
disconnect (or
power cable) on
systems wired
directly to
facility power.