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
To Next Page
Loading...
Need help?
General
