HP 54645A, User'S And Service Manual

Page: 233 / 301

6
Disconnect the ribbon cable from the display board, then check the
following signals on the system board.
Table 7-19 Display Signals
Signal Name Frequency Pulse width Voltage
U5 Pin 36 DE 19.72 kHz 38.0
µ
s 2.6 V
p-p
U76 Pin 1 (HP 54645A)
U77 Pin 1 (HP 54645D) Hsync 19.72 kHz 3.0
µ
s 5.0 V
p-p
U5 Pin 2 Vsync 60.00 Hz 253.5
µ
s 5.2 V
p-p
If the signals are good, replace the display assembly. If not, replace the
system board.
7
Disconnect the ribbon cable from the display board.
8
Go to "To check the Low Voltage Power Supply."
If the voltages are within the test limits, replace the display assembly. If not,
do the steps below.
a
Disconnect the power cord.
b
Disconnect the ribbon cable from the power supply.
c
Connect the dummy load to the power supply connector.
d
Connect the power cord, then measure the power supply voltages
again (see new tolerances below).
If the voltages are now within the test limits, replace the system
board. If not, replace the power supply.
Table 7-20 Low Voltage Power Supply Voltage Tolerances
Supply Voltage Tolerance
+
5.1 V
±
153 mV (
+
4.947 V to
+
5.253 V)
–5.25 V
±
158 mV (–5.092 V to –5.408 V)
+
15.75 V +1.260 V, –787 mV (
+
14.963 V to
+
17.010 V)
−
15.75 V
±
787 mV (
−
14.963 V to
−
16.537V)
Testing, Adjusting, and Troubleshooting
To check out the oscilloscope
7-44