Supplemental Troubleshooting Procedures; Checking The Crystal Oscillator; Checking The Reference Voltage; Checking Display Drive Voltage - Fluke II Series Service Manual

Maintenance
TROUBLESHOOTING
Supplemental Troubleshooting Procedures
3-16.
CHECKING THE CRYSTAL
OSCILLATOR
3-1
7.
Connect
an oscilloscope or counter
to
pin 54 of
U1
or
to the junction
of Cl
2 and
the
Y1
crystal.
Check
for a
32.768-kHz
sine
wave
approximately 600
mV
p-p
in amplitude.
Note
that
U2
and
the display will
not
work
if
the
clock
circuit
is
not working.
Probable
related failures include:
Ul, Yl,
or C12.
CHECKING THE REFERENCE VOLTAGE
3-1
8.
Check
for a reference voltage of 1.00V dc
(adjustable
by R8)
at
pin 14 of
Ul
or
at
the
junction
of
R15
and R16.
Probable
related failures include:
R8, R14, R15, R16,
VR1,
or
CR2.
CHECKING
DISPLAY DRIVE VOLTAGE
3-19.
Check
that
VM
(V
middle)
is
1.6V dc
±
.IV
at
pin
28
of
U2
or
at
the junction of
Rll
and R12.
Probable
related
failures include:
Rll
or
R12.
CHECKING BEEPER
DRIVE SIGNAL
3-20.
Put the unit in the Diode
Test
Mode
and
short the input leads.
Using
an
oscilloscope,
measure
the
signal
at
pin
3
of Ul.
The
signal should
be
a
4V
p-p symmetrical square
wave
at
about
4.1
kHz.
A
probable
related failure
is:
Ul.
TRACING THE
VDC
SIGNAL PATH
3-21
.
Use
the
following procedure
to trace the
VDC
signal path:
1.
Set the
UUT
to the
VDC
function
and apply
2V
dc
to the input.
2.
Using
a
DVM,
measure
the input
at J1
for
2V
dc.
3.
Measure
pin
1
of
Z1
input divider for
2V
dc.
Probable
related failures include:
Rl,
SI,
RV1,
or
RV2.
NOTE
Measurements
in
steps
4, 5,
and 6
may
be
affected
by
loading.
4.
Measure Z1
pin 3
for
200
mV
dc.
Probable
related failures are:
Zl, Ul.
5.
Measure
for
200
mV
dc
at
the active
filter
input (AFI,
pin
26 of
Ul
or R9).
A
probable
failure
is:
Ul.
6.
Measure
for
200
mV
at
the active
filter
output
(AFO,
pin
27 of
Ul
or R9). Probable
related failures
are:
R9, C5, or C6.
WARNING
Rl
IS
A
FUSIBLE RESISTOR.
TO ENSURE
SAFETY,
USE EXACT
REPLACEMENT
ONLY.
3-11