Ilt4 Front Panel Display Troubleshooting; Symptom: Dark Display - Agilent Technologies PSG Series Service Manual

ILT4 Front Panel Display Troubleshooting

Overview
The Front Panel Display Assembly consists of the A1 Keyboard, A2 Display (640 x 320 pixels Liquid Crystal
Display), A3 Power Switch, and the A4 Inverter dc to ac). The A4 Inverter turns the A2 Display on and off via
control lines received from the A18 CPU. The A4 Inverter also converts the 5.2 Vdc to approximately a 160
Vrms, 40 kHz signal to drive the A2 Display.
The A3 Power Switch contains the power on/off switch, standby LED, and power-on LED. The A3 Power
Switch also contains the circuitry to pull the ON_OFF control line to a TTL low and disable the power supply.
Another function of the A3 Power Switch is to route the 8 data bits from the A18 CPU to the A2 Display.
A2 Display Contrast Controls
There are two contrast hardkeys below the A2 Display. The left up arrow key increases the contrast while the
right down arrow key decreases the contrast.
The A2 Display brightness can be adjusted from 50 (high brightness) to 1 (low brightness) using the RPG,
arrow keys, or the numeric keypad.
Softkey Location: Utility > Display > Brightness
A2 Display Tests
There are two screen tests for the A2 Display. The Black Pixel Screen Test will turn the display dark and the
White Pixel Screen Test will turn the display bright.
Softkey Location: Utility > Display > More (1 or 2)
To exit the test press any front panel key.

Symptom: Dark Display

Ensure that the signal generator is powered-on and the front panel green LED is lit. If the green LED is not
lit refer to the Power Supply Troubleshooting section in this manual. Press any front panel key to disable the
screen saver.
If the A2 Display is still not working, check P12 on the A31 Motherboard for the signals in table 1-8.
Table 1-5
P12-1
P12-3 LIGHT_EN
P12-4 VDISP
If the 5.2 Vdc line is bad refer to the Power Supply Troubleshooting section in this manual. If either the
LIGHT_EN or VDISP are bad, check them at P221-16 and P221-55 respectively on the A31 Motherboard. If
either signal is bad at P221, then replace the A18 CPU.
If the above signals are good, check the A4 Inverter output. To check the A4 Inverter output, the front panel
has to be removed from the chassis frame and laid face down. With CN2-1 (A4W1) open there should be a
160 Vrms 40 kHz signal. If you don't see this signal, replace the A4 Inverter. If the signal is present at the
A4 Inverter output, then replace the A2 Display.
Signal
-5.2 Vdc
>3 Vdc
Brightness=50, VDSP < 50 mVdc
Brightness=1, VDSP = 3 Vdc
Getting Started with Troubleshooting
State
Troubleshooting
1-9