HP 54645A User's And Service Manual page 233

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