Front Panel Pca; Leds; Key Pad - HP DesignJet 200 Service Manual

Front Panel PCA

The plotters use the same front panel PCA as the DeskJet 550. The front panel consists of
nine LEDs and eight switches, mounted on the PCA, which is deeply recessed behind a plastic
housing containing the key pad. The keys act on the switches through push rods. Light pipes
transmit the light from the LEDs to the display area.

LEDs

The LEDs are driven by drivers on the main board, under the control of the servo processor.
The LED layout is shown below:
led[1]
led[2]
led[3]

Key Pad

The keypad layout is shown below:
led[2]
Switch[1]
Switch[5]
The switches are connected as a 4x2 matrix. The switch matrix, when scanned, is driven by
the four LED control signals led[2], led[3], led[6] and led[7]. The servo processor scans the
switch matrix by setting, in turn, each of the four control signals to `0' while holding the
other three at `1'. While driving the switch matrix, the processor reads the signals key[0],
and key[1]. A `1' on a key signal indicates a closed switch.
C3187 90000
led[4]
led[5]
led[6]
Front-Panel LEDs
led[3]
led[6]
Switch[2] Switch[3]
Switch[6] Switch[7]
Front-Panel Key Pad
led[7]
led[8]
led[9]
led[7]
key[0]
Switch[4]
key[1]
Switch[8]
Functional Overview 5 31