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Keyboard
Signals
Isolate a faulty elastomeric keypad or keyboard when the random key(s) are not
Check
operating by performing the following steps.
1. Turn off the instrument and remove the power cable.
2. Without disconnecting the keyboard cable, follow the keyboard removal
procedure to loosen the keyboard. Leave the keyboard in place in front of
the instrument.
3. Reconnect the power cable and turn on the instrument.
4. Run the Keyboard Self Test and press all of the keys.
5. Allow the keyboard assembly to fall forward from the front panel. Separate
the elastomeric keypad and keyboard panel from the PC board.
6. Short the PC board trace (with a paper clip or screwdriver) of the
non-operating
key and look for an appropriate
response on the display.
7. If the display responds as if the key were pressed, replace the elastomeric
keypad.
8. If the display does not respond as if the key were pressed, replace the
keyboard.
The RPG connector has a TTL pulse on pins 1 and 3, when the knob is being
turned.
Pin 5 of the connector is + 5 V.
The ROW (scan) signal is a low duty-cycle pulse at approximately
60 Hz. It is
continually present on pins 14 through 20 of the keyboard cable. Because of the
resistance of the keypad contacts, the signal does not appear the same on the
COLUMN
(data) pins when keys are pressed. Refer to the following table for
signals going to and from the keyboard.
Table 6c-3.
Keyboard
Connector
Voltages
and Signals
PIN
SIGNAL
1
3
5
7
9
11
13
15
17
19
GROUND
2
COLUMN 6 (Data)
4
GROUND
6
RPG
(DIRECTION)
8
COLUMN
5 (Data)
10
COLUMN 3 (DATA)
12
COLUMN
1 (DATA)
14
ROW 5 (Scan)
16
ROW 3 (Scan)
18
ROW 0 (SCAN)
20
PIN
SIGNAL
GROUND
+5
V
(DIGITAL)
RPG
(CLICKS)
N/C
COLUMN
4 (Data)
COLUMN
2 (DATA)
ROW 4 (Scan)
ROW 2 (Scan)
ROW 1 (Scan)
ROW 6 (SCAN)
Troubleshooting
HP
16528/1653B
6c-14
Service Manual
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