Fluke PM6681 - Page 54

Power
Supply
(Functional
Level
1)
Figure
5-7
Test
points
and
voltages for
the power
supply.
WARNING:
Live parts and
accessible
terminals
which
can
be dangerous to
life are always
exposed
inside
the unit
when it is connec-
ted to
the line
power.
Use
extreme caution
when
handling, testing or
adjusting the
counter.
Primary
circuits
To verify the
Power supply proceed
as follows:
-
If
the primary
fuse is broken, there is a short
circuit
in
the
primary
circuits.
Use a DMM and try to iocate the
fauit
by
resistance
measuring.
-
Remove the
cover from the Power Supply.
WARNING:
The
heat
sink inside
the
power
supply is
connected to
the
line power.
-
Disconnect
L39 and L40 and
check the resistance be-
tween pin
1 and 4 on the
transformer
T1, see Figure
5-7.
if
the DMM
show
a
short
circuit the fault is
proabably
a
broken transistor
V55.
Put
L39 and L40 back in
position.
-
Connect
the counter to the
iine
power via an insulating
transformer
with separate
windings.
-
Set
the counter to
STAND-BY
mode.
-
Check
that the
voltage between P19
and
P23 is in the
range
of 90 to 260
Vac.
-
Check that the
DC voltage
between pin 1 and 4 on T1
is
about
-^2
times
the input
AC-voitage. if not, use
traditio-
nal
fauitfinding
techniques to
locate
the fault.
-
Remove the jumper J15.
-
Check the
"STAND BY"
voltages according to Table
5-5.
Test points
Ground
Voltage
U91
pin
11 & 12 U91 pin 8
+10
to
+13.5
V
U91 pin 14
U91 pin 8
-+5.0
V
V55
source U91 pin 8
=+10
mV
U90 pin 1
L41 =+8.2
V
U92 pin
1 L41
=+4.4
V
X10
L41
=+5.1
V
XII
L41
+14.8
V to
+21
V
X12
L41
-12.5
V to -7.5 V
X13
L41
+12
V+0.5 V
Table
5-5
Stand-by
voltages.
-
Reinstall the
jumper
J15.
-
Check the
curveforms according
to Figure
5-8
and
Figure
5-7
to verify the
primary
circuits. Use the heat-
sink
of V55 as ground.
Figure
5-8
Typical curves of
the
power supply.
NOTE: U91
and U92
are
located
at
the bottom side of
the
PCA.
Secondary
circuits
“
Connect
the power
cable to the counter.
-
Switch ON the counter.
CAUTION:
If you
adjust
the
+5
V trimmer you
have to
adjust the complete
instrument.
5-6
Troubleshooting