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Table
5-5.
Display
Checks
Step
Item/Component
Required Condition
Remarks
1
Turn on power.
Any
function
or range,
except
OHMS.
2
+ 5V
Pad*
or
J1001,
pin
7
+ 5V
±5%
If
low,
check
per Table
5-3
3
U202,
pins
2. 6, 7,
9
and
13
Digit drive.
Low =
Enabled
LED
Cathode
4
U203,
pins
1,
2,
6
and 7
HI
=
Enabled
BCD
input to
U203
seg-
ment
decoder/drive
5
U203,
pin
2
Negative-going
signal
lasting
for
200 dock
pulses.
Leading
digit
suppres-
sion.
6
J1001,
pin
2
Polarity
Line
(sign)
HI
=
Off
LO =
-
Polarity
output
is
dis-
abled
on
AC
an
D.
7
J1001,
pin
4
J1002,
pins
1,
11
&
12
Appropriate
DP
line
high
(on).
Depress
RANGE
push-
buttons
to
check
all
DPs.
*0n
main
printed
circuit
board.
See
Figure
5-1.
Table
5-6.
A/D
Converter
Checks
Step
Item/Component
Required Condition
Remarks
1
Turn
power
on. Select
2VDC
range.
2
Display
.0000
+
1
digit
3
TP1*
O.OOOOV
Input
to
U106,
Chopper
out-
put.
4
TP2*
-M.OOV
Reference
output.
5
Short
TP1
to
TP2.
Connects
reference
output
to
U106
input.
6
Display
1.0000
±2
digits
If
steps
4
and
6
are correct
A/D
converter
is
functioning
properly.
If
not,
continue with
step
7.
7
TP4*
0
to
+
5V
square
wave
at
100kHz
-H
100Hz.
Clock
input
to
U106.
8
TP3*
+
1.0
±0.1V
Stored autozero
voltage.
9
U105,
pin 11
+
1.0
±0.1V
E-node
voltage
to integrator
in
U105.
10
U105,
pin
14
-1.2
±0.2V
U105
integrator
output
voltage.
11
U105,
pin
13
+
1V
U105
buffer input.
12
U105,
pin
9
+
1V
U105
buffer output.
13
External
Voltage
Source.
Apply
+
1.9000V
Calibration point.
14
Display
1
.9000
±
1
Digit
If
different,
check
U106
input.
15
TP1
1.9000V
Input to
U106.
16
U105,
pin
14
Waveform
per Figure
5-2.
Integrator
output.
17
U105,
pin
2
Waveform
per Figure
5-2.
during
ramping
in
integrator.
Comparator
output.
*0n
main
printed
circuit
board,
see
Figure
5-1.
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