The current draw of the GSI 17 can be checked by connecting an
ammeter in place of the power switch.
The current draw in the
active mode should be less than 75 ma. In the sleep mode the
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.
The driver
for the Display
(U501)
sources each segment with a square wave of
approximately 36 Hz (28 ms) with a
50/50
duty cycle.
All
segments of the LCD have a commonconnection 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.
For the
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
8
oing to be illuminated
are driven with a square wave that is 0
or in phase with the
Back Plane.
When the two signals present at the LCD segment are
in phase there is no potential across the segment and the segment
is OFF.
When the two signals are out of phase there is 5 V
potential present a all times and the segment is ON.
Generally,
if a segment is missing an AC meter can be used to check for
proper phase relative to the Back Plane.
An AC measurement of 5
V would indicate the signals are out of phase and that the
segments should be illuminated.
An ac measurement of 0 V would
indicate that
the
signals are
in phase.
An ac measurement
relative to ground should indicate 2.5 VRMS.
This would indicate
the presence of a square wave.
A dc measurement of 0 Vdc or 5
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
The Pushbutton Diagnostic
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.
54
To Next Page
Loading...
