Service manual

PN 4237242C
2.2-1
INSTRUMENT DESCRIPTION
POWER SUPPLY
2
2.2 POWER SUPPLY
Overview
Ac is input into the lower chassis using a connector that is also a line filter. Both lines are
fused, F1 on the hot line and F2 on the neutral line. For 120 Vac units, a 4.0-A SLO-BLO fuse
is used, and for 220 Vac units a 2.0-A SLO-BLO fuse is used. Additional conditioning is
provided by the Transient Voltage Suppressor card, a simple circuit card comprised of a gas
tube surge arrester and three varistors, connected in parallel to the incoming ac line. The ac
voltage is then made available to the AC Power/Vacuum Relay card and the AT power supply,
a PC-type computer switching supply in the upper chassis.
System power is turned on using the switch built into the AT power supply. This provides
±5V and ±12 V to the computer in the upper chassis and any cards using the computer bus.
The User Resource Adapter (URA) card routes +5 V from the AT motherboard to the LCD
screen resulting in two solid bars being displayed. System software controls the display, so no
further screen image is seen until the system software is loaded from the Program Disk and is
executed.
Connector P2 of the AT power supply also provides +12 V directly to the AC Power/Vacuum
Relay card, energizing relay K2 and routing ac to transformer T1 and the +24 V switching
power supply. Three transformer secondary voltages provide input ac to the Linear Power
Supply card, which immediately makes available ±15 Vdc, aperture and aperture zap voltages
and the Hgb LED (Light Emitting Diode) current. When the system software has been loaded
and is in control, the Diluter Resource Adapter (DRA) card sends a command to the
Motor/Solenoid Driver card to turn on the +24 V.
AT Power Supply
The AT power supply is found in the upper chassis (see Figure 2.2-1) and is a PC-type,
200-W, switching power supply, providing ±5V and ±12 V (Table 2.2-1). It has a built-in
cooling fan that provides air flow to the upper chassis area. Its Power On/Off switch also
serves as the instrument’s Power ON/OFF switch.
The power supply is purchased as a unit and should be replaced as a unit. Schematics and
component parts are not available.
Inputs
Standard ac line cable input connector
Outputs
Table 2.2-1 AT Power Supply Output Connectors
Connector Type Volts Supplied Description
P1 Low-power utility +5, +12 1.0 A
P2, P3 High-power utility +5
+12
1.8 A
2.8 A
P4, P5 AT power supply
±
5,
±
12 To AT motherboard
C