Troubleshooting The Display; Switch Related Failures - Welch Allyn Grason-Stadler GSI 17 Series Service Manual

The current draw of the GSI 17 can be checked by connecting an
ammeter in place of the power switch.
active mode should be less than 75 ma.
current draw should be reduced to approximately 16 ma.

6.8 TROUBLESHOOTING THE DISPLAY

Refer to the Calibration Mode, Section 4, for method of entry
into the Display Diagnostic Mode (D2).
The LCD Display is relatively easy to troubleshoot.
for the Display (U501) sources each segment with a square wave of
approximately 36 Hz (28 ms) with a 50/50 duty cycle.
segments of the LCD have a common connection via BP1 and BP2.
This Back Plane (BP) is driven continuously with a 36 Hz square
the same frequency that the segments are driven at.
segments to be illuminated (black) they must be driven with a
square wave which is 180' out of phase relative to the Back Plane
square wave. Any segments which are not
are driven with a square wave that is 0
Back Plane. When the two signals present at the LCD segment are
in phase there is no potential across the segment and the segment
When the two signals are out of phase there is 5 V
is OFF.
potential present a all times and the segment is ON.
if a segment is missing an AC meter can be used to check for
proper phase relative to the Back Plane.
V would indicate the signals are out of phase and that the
segments should be illuminated.
indicate that the signals are in phase.
relative to ground should indicate 2.5 VRMS.
the presence of a square wave.
Vdc would indicate steady state or a possible open connection.
With this information it should be relatively easy to establish
if the driver or LCD segment is at fault.

6.9 SWITCH RELATED FAILURES

Refer to the Calibration Mode, Section 4, for method of entry
into Pushbutton Diagnostic Mode D
test can be used in troubleshooting all the front panel switches
and dip switches independent of their Normal Mode functions. It
should be relatively easy to isolate switch failures using this
mode.
The current draw in the
In the sleep mode the
oing to be illuminated
or in phase with the
An AC measurement of 5
An ac measurement of 0 V would
An ac measurement
This would indicate
A dc measurement of 0 Vdc or 5
The Pushbutton Diagnostic
The driver
All
For the
Generally,