HP Apollo 9000 400dl, Servicing Manual, Page: 69 / 296

Theory of Operation 3-19
• VRX Monochrome Graphics Controller Board (HP A1096A). This board is a
high-resolution, 19-inch monochrome display controller that has the following
features:
– High-resolution, 1280 x 1024 display
– Flicker-free, 72-Hz, noninterlaced screen refresh
– Low power requirements
– 256-KB image memory, using high-density dynamic dual-ported video
RAMs
The image memory stores a bitmap of the images that the controller displays
on the monitor. To display the images, the controller scans the bitmap and
sends the image to the monitor in a serial bit stream via a coaxial cable.
3.2.9 Power Supplies
Power supplies for Model 400t/400dl and Model 400s systems are autoranging units
that automatically adjust to a 100 – 120 or 220 – 240 V ac input voltage. The on/off
switch for these supplies does not control the ac voltage input to the supplies. The sup-
plies receive ac power when plugged into a wall outlet. The on/off switch turns on the
dc output of the supplies by passing a low-level dc control voltage and input signal.
Model 400t and 400dl Power Supply
The power supply for Model 400t and 400dl systems contains a voltage margin feature
that enables the CPU to alter the n 5V output voltage by five percent above or
below nominal. This power supply houses a two-speed fan. A thermistor on the CPU
board controls the fan speed according to the inlet ambient temperature of the system
unit. The Model 400t and 400dl power supply distributes dc voltages through the CPU
board to individual assemblies. For the Model 400t, the power supply also distributes
dc voltages directly to any internal disk drives through cables.
Model 400s Power Supply
The Model 400s power supply doesn’t control fan speeds or have a voltage margin
feature. The power supply distributes power through the motherboard and cables to
individual assemblies, as shown in Figure 3-6.