Keithley 172A Instruction Manual page 94

MAINTENANCE
INSTRUCTION MANUAL
Digllrl Mulllm~lw
Models
172A, 1?3A
TABLE 6-8 (coN~T)
:) One display bar
missing on all
digits.
I) Faulty connection be-
Check plug P3Ol and mating conn-
tween P301 & J301.
ector J301. Make certain all pins
are making contact.
2) Cathode driver cir-
"a" bar: Check R302 pin I4 for
cui try faulty. See signal.
schematic 27404~.
When "ON", vo I tage
should be approx. +l.av.
"b" bar: Check R3O2 Pin 16
"c" bar: Check R302 pin I5
"d" bar: Check R302 pin 9
"e" bar: Check R302 pin I2
"f" bar: Check R302 pin IO
"g" bar:
Check R302 pin I3
decimal point: Check R302 pin II
f) One digit missing.
I) Faulty connection be-
Check plug P301 and mating
tween P301 t J301. connector J301.
2) Anode drive circuitry If units digit missing, check
faulty. See schematic collector of Q305 for signal.
27404D. When "ON" voltage should be
approx. 418~.
If terns digit
missing, check collector of Q304.
If hundreds digit missing, check
collector Q303. If thousands
digit, minus sign and function
indicator missing, check collect-
or Q302.
9)
10,000 digit missing. Q30 I
On 10,000 digit, check collector
(except if reading is
Q301.
If no signals are present
less than 10,000
problem could be transistor or
counts)
integrated circuit U301.
h) Function indicator
Trans i star Q306
off.
i)
Faulty reading on
I)DMM set for 4 WIRE ohms Set to 2 WIRE.
R function.
and fi SOURCE terminals
are not connected.
2)DMM set for 4 WIRE ohms Connect HI input to the same side
but leads are reversed.
of unknown as the + ii SOURCE Lead
j)
Faulty reading on
Current fuse F5Ol is Replace fuse on rear panel.
Current function.
blown.
k) Faulty reading on
A/D converter circuitry. Check for proper Capture Range of
all functions.
See schematic 29145E, A/D converter as described in
Sheet 2.
Table 6-10.
6-18