Fluke 8506A Instruction Manual page 151

8506A
Table
4-24.
R 2
A/D
Converter Troubleshooting
SYMPTOM
Display Blanks
Improper Readings,
Inoperative A/D, Nonlinear
Readings
Flickering
Display
Direct
Address
IC4,
3,
&
2
High
Indirect
Address
U33, U34,
U35
(Affecting ID Lines)
Check
Transistor
Array Outputs
to J1
and
J2
—
The
rise
and
fall
times
of
these Switching Pulses
Must be <2
jjsec.
Autozero
Control
—
U25,
U34
IDO
=
1
=
Reset
Counter
ID1
=
1
=
Auto Zero
I
D2
=
0
—
Buffer Input
102
=
1
=
Remainder
Input
ID3
=
1
=
Channel X (Auto Zero
and remainders
1
and
3)
103
=
0
=
Channel Y (Remainders
2
and
4)
IC2
&
1
High (and Ring Counter
not
in
CO
time
period,
CO
—
0)
This
Indirect
Address
allows the ID7 enable
to
bring
back
Polarity Bits to
the Controller
Module
First
Check TPS
—
Should be
switching
between
+
and
-7V. Typical
failures
in
this circuit result
in
a portion
of
the
switching slope having
a
slew
rate less
than
1V///sec.
A
glitch
at
the
zero
point
is
normal.
SYMPTOM
POSSIBLE FAILURE
Noisy Readings
U1, U2,
U3
Nonlinear
Ladder
U4,
09,
Q10
(Q27)
Ladder
out of
Tolerance FETS Q11-Q15
or
Q17-Q21
All
Digits
Wrong
U7,
Q31
,
032
Reading Locked
(Doesn't
Respond
to
Input
Change)
or
Always
Overrange
U4, Q9, U1, U2, U3, Q2,
Q3
Bad Remainders
(Lesser
Digits) Q22, U4,
U6
No
Polarity Bit
Returned
Q29,
Q28
Shifty
Readings (Most
or
all
Digits)
Autozero
Settling
Time Problems
U8,
Q30-Q8,
Q7
NOTE:
If
U1
,
R9, R1 4-R16, R34, R35, R50-55, R67,
Q1-Q3, 01
1-016, Q25, or
Q26
are
replaced
it
will
be necessary
to
return the
module
to the factory
(attn.
PARTS)
to
be temperature compensated anew.