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71
4.
FAULT-FINDING
4.1.
GENERAL
4.1.1.
Service hints
If
servicing
is
necessary the following points
should be taken
into
account
in
order
to avoid
damaging
the
instrument.
—
Take
care to
avoid
short-circuits
with measuring
clips
and hooks
if
the instrument
is
switched-on,
especially
near
the input
terminals
when
high-voltages are present.
—
Use
a
miniature
soldering iron
(35W
max.) with
a thin cleaner
or
a
vacuum
soldering
iron.
—
Use an
acid-free solder.
—
When
fault-finding,
remove
top and
bottom
covers
and
make
sure that
the
POWER
SUPPLY
is
connected
with the
main
board.
—
After
repair,
the instrument should be
recalibrated.
4.1.2.
Fault-finding
procedure
This
chapter
gives a fault-finding
procedure to
locate
the
faulty section
in
the instrument.
From
this
procedure
the faulty
parts
can often be
found by
using the detailed
flow
charts.
NOTE:
The
procedure
is
only intended
as
an
aid
to fault-finding,
and
abviously
that the faulty
component
will
not be
found
in
every
case.
Measuring instruments
used:
—
Digital
multimeter.
—
Oscilloscope.
—
Counter.
4.1.3.
Fault-finding
with the
signature analyser
When
the
normal
fault-finding
does not
find
the
fault,
then
it is
possible
to use
a
test-ROM.
The
testrom with
several tests for
the
PM2521
is
based
on
signature
analysis.
It
can
trace
faults
at
component
level
for
the
controller section, display section
and
even
a
part
of the analog
section.
The
signature analysis fault-finding
consists
of
a:
—
Testrom
with the following
tests:
—
Free run
tests
—
RAM
and
I/O
test
-
Visual L.C.D.
test
(noS.A.)
—
Switch decoding
test
—
Relay/FET
test
—
Static
relay/FET
test
(noS.A.)
—
Counter
test
—
Interrupt controller
test
—
Test
service
note
which
includes:
—
Description of
how
to use the signature analyser
—
Circuit
diagrams with
signatures
The
test—
ROM
and
the
service
note can be ordered
from Concern
Service
under code
nr.
5322 694
54013.
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