Fluke 8506A Instruction Manual page 154

8506A
Table 4-25.
Thermal True
RMS
Converter
Module
Troubleshooting
(coot)
B
I
Hi
ACTION
Go
to the step
number
given
for correct
response
VES
NO
18
Is
the
resistance reading
294
ohms
±7%
between TP1 and
TPS,
and 389
ohms
±8%
between TP1
and
TPS?
19
20
19
Check
in
sequence
the following items
on
the Amplifier PCB:
a.
Switching
transistors
Q26, Q12, Q14, Q16, and
their
associated components.
b.
Q28
and
its
associated
components.
3.
Q19, Q18, Q31,
and
their
associated
components.
d.
Q10, Q8, and
their
associated components. {The
gate voltages on
Q8
and Q10
normally vary approximately IV from
off to on.)
e.
Amplifier
U1 and
its
associated
components.
Repair as required then resume
at
step
4.
20
Check
the
RMS
Sensor using
the
procedure
in
Tabie
4-26. Repair
or replace
then
resume
at
step
4.
21
Does
the
fault
occur
only
if
the high
accuracy and/or
the
fast
enhanced
modes
are
selected? 22
26
22
Connect
a test
DMM
between
TP8
(HI)
and TP1
(LO)
on
the Amplifier
PCB,
then apply
a
full
scale voltage
input to
the
UUT
terminals.
(Apply an
input
equal
to
the
full
scale reading
rather
than
the
range
title
of the defective range.).
23 With the high accuracy
mode
selected,
does
the reading
at
TPS
remain
stable
(±50 uV)
after
the
initial
settling period of
approximately
0.5
second
(the settling period repeats
every 3 seconds).
24
25
24
Check
the sensor adjustment portion
of the Calibration Procedure. Adjust or
repair
as
required then resume
at
step
4.
25
Check
U11, U12, Q19, Q18, Q31,
and
their
associated components.
Repair as required then
resume
at step
4.
26 Select the
AC
Normal
+ DC
Volts function
and
Autorange. Apply
a
IV dc
signal to the
UUT
input terminals.
27 With the instrument
still
in
Autorange and
the
input
unchanged,
select
the
AC
Volts
Normal
function.
28
Is
the instrument reading within the required tolerance with the
AC
Normal
+ DC
Volts
function selected
and
approximately zero with the
AC
Volts
Norma!
function selected?
29
Check
the following items
in
the
sequence
listed until the
fault
is
located, repair
as
required,
then resume
at
step
4.
If
the
fault
is
not located
in
one
of
these
areas,
proceed
to
the next step
in
the table.
29 37
a.
K2 and K3
on
the
Attenuator
PCB
for the proper switching
action.
b.
Cl through C4 on
the Attenuator
PCB.
c.
U3 and
its
associated
components on
the Amplifier PCB.
d.
Voltages
at
Q1-7
using the typical voltages
in
Table 4-27.
e.
Attenuator
circuits
on
the Attenuator
PCB.
4-40