User's Manual

Corrective Maintenance
7.5 Miscellaneous Functions
7
7-11
7.5.4 Keyboard
Proceed as follows if one or more keys cannot be operated.
1. Replace the key pad, and the key pad foil to see if this cures the problem.
2. Press a key, and check ROW0...5 (measure spots MS432..MS437) for the signal
shown below :
≈
50 ms
500
µ
s pulsesPress key
0
V
+3.3
V
Release key
If no key is pressed the ROW lines are low if a battery is installed; if the 123 is
powered by the the mains adapter only, the lines are alternating pulsing and low.
3. Check COL0...3 (measure spots MS438...MS441) for a +3.3V level. Then press and
hold a key, and check the matching COL line for the signal shown below:
≈
50 ms
500
µ
s pulsesPress key
0
V
+3.3
V
Release key
If not correct, check the connections from X452 to D471; replace D471.
For the ON/OFF key see Section 7.5.13.
7.5.5 Optical Port (Serial RS232 Interface)
Receive (RXD)
1. Check the voltage RXDA on TP522 for +200 mV, and the voltage RXD on TP527
(buffered and amplified RXDA voltage) for +3.3V.
2. Shine with a lamp in the optical port (H522).
Check the voltage RXDA on TP522 for 0...-0.6V, and the voltage RXD on TP527 for
0V.
Send (TXD).
1. Check the voltage TXD on TP521 for +3.3V.
2. Press
to open the SAVE & PRINT menu.
3. Press PRINT SCREEN to start the test tool data output.
Check the voltage TXD on TP521 for a burst of pulses (pulses from +2V to +3.3V).
The length of the burst and the pulses depends on the selected baud rate.
7.5.6 Channel A, Channel B Voltage Measurements
1. Press to open the SCOPE INPUTS menu, and select:
INPUT A: ■ DC | ■ NORMAL | INPUT B: ■ DC | ■ NORMAL