To Check The Keyboard; Troubleshooting Attenuator Failures - HP 54520 Series Service Manual

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CAUTION
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To check the keyboard
To check the keyboard
Use the following steps to isolate a faulty elastomeric keypad or keyboard when random keys
are not operating.
Remove the power cable.
Without disconnecting the keyboard cable, use the keyboard removal procedure in
chapter 6 to loosen the keyboard. Leave the keyboard in place in the front of the
instrument.
Replace the power supply.
You can leave the disk drive connected. Just set it to the side, out of the way.
Apply power with a key-down powerup.
Run the keyboard selftest to determine the failed keys.
a Press Utility ,thenpressselftest menu.
b Select misc then keyboard, then press start test.
ec Check the keyboard.
1 Press each key once.
2 Follow the instructions on the screen to check the LEDs.
3 Rotate the RPGs
4 Press Run twice more to exit.
Remove the keyboard assembly from the front panel.
Be careful not to contaminate the key side of the PC board or the keypads. Dust and
fingerprints on these parts may cause intermittent key operation.
Separate the PC board from the elastomeric keypad and keyboard panel.
a Remove two screws.
b Slide the plastic keyboard spacer down until the tabs at the top are clear of the
keyboard panel.
e Lift the top of the spacer away from the keyboard and slide the spacer out of its
bottom mounting.
d Lift the keyboard off of the keyboard panel and keypad.
Carefully short the PC board trace (with a paper clip or screwdriver) at the
nonoperating key (as determined by keyboard test) and look for an appropriate
response on the display.
If the display responds as if a key were pressed, replace the elastomeric keypad.
If the display does not respond as if a key were pressed, replace the keyboard.
Reassemble the instrument.
Troubleshooting attenuator failures
Checking the signal output of the attenuators on the surface-mount PC board is not practical,
so the best method for troubleshooting attenuator failures is to swap the suspected one with a
known good one. The following discussion will help you determine whether the attenuator or
PC board is causing a problem.