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CT 9000 ® ADV
MOTHERBOARD
The MOTHERBOARD consists of the following major components,
each of which will be discussed in greater detail in the following
sections:
* Power Supplies
* Powerhead Interface
* Servo
e Auxiliary I/O Interface
* Handswitch Interface
e Status LED's
e Console Connectors
Power Supplies
The power supply section consists of four major functional sections:
Remote on/off, +3.5V supply, +5V supply and +12V supply.
Remote On/Off
The main power transformer supplies 24VAC to the motherboard.
One side of the 24VAC goes directly to a diode bridge, BR1.
The
other side of the 24VAC goes through a solid state relay, SSR1,
and then to the diode bridge. The solid state relay is controlled by
U17. When the solid state relay is off, the 24VAC is not applied to
both sides of the bridge and, therefore, the +5V and +12V supplies
are off. However, U17 requires power to operate the remote on/off
function, so the +3.5V supply is used to power U17 while the +5V
and +12V supplies are off.
The Power Supply Control Input (/PSI, U17 pin 8) and Power Sup-
ply Control Output (/PSO, U17 pin 16) are used to control tne solid
state relay. Prior to establishing a voltage on VCC (U17 pin 3), PSI
is internally held at a high level at ail times by the +3.5V supply on
VBAT (U17 pin 1). When /PSI is forced low by the motherboard
reset switch, SW1, or by the momentary switch on a console, PSO
is connected to VBAT to provide a high level. This high level turns
on the solid state relay. A subsequent falling edge on /PSI will
tristate PSO to shut off the solid state relay.
Relay K3 is used to isolate +5V from U17 pin 3 until the solid state
relay turns on. This, along with a filter formed by L3 and C34,
helps to eliminate noise related problems.
Opto-isolator U18 is used to interface /PS! to the console switches
and the motherboard switch, SW1.
Capacitor C8 is placed across
the LED side of U18 to prevent it from inadvertently turning on
when a long console cable is attached.
3-6
800961-C Nov. 2000
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