Agilent Technologies E4991A Service Manual page 159

Step 1. Check LED on A50 Power Supply
From the E4991A rear, check the LED inside of the lattice of the rear panel as shown in
Figure 4-4. If the LED doesn't light, the A50 Power Supply assembly is failure.
Figure 4-4 LED on the A50 Power Supply
Step 2. Check power LED
If the power LED on Front Panel doesn't light and the fans inside of the E4991A doesn't
run, problem seems in the A21 Analog Interface board or the flat cable between the A21
and the A22 Front Panel Keyboard.
If power shutdown occurs immediately after the power LED lights, there is a possibility
that the fan stops. The E4991A has three fans inside. There is one CPU fan on the A20
Digital Motherboard. There are two system fans which are secured on the frame. A power
shutdoun occurs the moment the system fans stops. In this case, remove the E4991A outer
cover and make sure whether the fans run or stop.
Chapter 4
Troubleshooting
No Display Troubleshooting
159