Operating instructions

TECHNICAL DESCRIPTION
4-3
The DC output circuits producing the four output supplies are each fed from an individual winding
on the DC-DC converter output transformer.
Regulation is applied to the DC-DC converter from the output current and voltage sensing circuits.
Current monitoring to provide regulation is obtained from the three common-return supplies and
voltage monitoring from the +5 V supply.
The 36 V output is generated by adding a 24 V floating supply onto the +12 V supply rail. The
floating 24 V supply has a voltage regulator configured within it.
A control circuit PCB contains the components for frequency control and voltage regulation of
both converters.
The external DC supply is not switched directly; the 3rd pole of the power ON/OFF switch
controls the DC-DC converter, thereby switching the DC supply to the Service Monitor.
The display
The display device is a color transflective TFT liquid crystal display module with an active
viewing area 143 mm x 80 mm. It comprises the display module, a driver board, and a cold
cathode fluorescent tube (CCFT) backlight.
The viewing area is composed of a 1200 X 240 RGB dot matrix. Each pixel is sequentially
addressed with a 6-bit data bus to determine its color and intensity. The display contrast is fixed,
but the brightness can be adjusted over a small range by varying the backlight drive. This is
achieved by generating a programmable voltage on the microprocessor board and feeding it to the
backlight inverter, mounted on the rear of the display module. The inverter produces
approximately 1500V for the CCFT backlight. In high ambient light conditions the backlight can
be switched off to conserve battery power.