Keithley 177 Instruction Manual page 34

Table 6-5. Display Checks
Step Item/Component Required Condition Remarks
1
Turn on power. Any function
or range, except OHMS.
2 +5V Pad* or JIOOI, +5v *5% If low, check per Table
pin 7 5-3
3 U202, pins 2, 6, 7, Digit drive. Low = Enabled
LED Cathode
9 and 13
4
Ki3; pins 1, 2, 6 HI = Enabled BCD input to U203 seg-
ment decoder/drive
5 U203, pin 2
Negative-going signal lasting Leading digit suppres-
for 200 clock pulses. sion.
6 JIOOI, pin 2
Polarity Line (sign)
Polarity output is dis-
HI = Off abled on AC an a.
LO = -
7 JIOOI, pin 4
Appropriate DP line high (on). Depress RANGE push-
J1002, pins 1, 11 &
12 buttons to check all
DPs.
'On main printed circuit board. See Figure 5-l
Table 5-6. A/D Converter Checks
St;p 1 Item/Component
2 Display
3 TPI *
4
TPZ*
5
6 Display
7
TP4*
8
TP3*
9 U105, pin 11
10 U105, pin 14
1: U105, U105, pin pin 9 13
13 External Voltage
Source.
14 Display
15 TPl
16 U105, pin 14
17 U105, pin 2
*On main printed circuit board, see Figure 5.1,
+ l.OOV
Shot? TPI to TP2.
1 .OOOO k2 digits
0 to + 5V square wave at
IOOkHz f IOOHz.
+1.0 *O.lV
+1.0 *0.1v
-1.2 f0.2V
+1v
+1v
Apply + 1.9OOOV
1.9000 * 1 Digit
Remarks
Input to U106. Chopper out-
' put.
Reference output.
Connects reference output
to U106 input.
If steps 4 and 6 are correct
AID converter is functioning
properly. If not, continue with
step 7.
Clock input to U106.
Stored autozero voltage.
X-node voltage to integrator
in U105.
U105 integrator output
voltage.
U105 buffer input.
U105 buffer output.
Calibration point.
If different, check U106
input.
Input to U106.
Integrator output.
Comparator output.
5-8