Philips PM2521 Service Manual page 175

3
Test 5 (counter
test)
Test 5 activates
the counter and counter input control
circuit,
and the
AZC
flip-flop
D1903.
Signature analysis
is
possible.
Test
6
(interrupt controller
test)
Test
6
activates
the interrupt control
circuit.
Signature analysis
in
this test
is
also possible.
NOTE:
AH
the
signatures are given
in circuit
diagrams.
The
signatures
signed with a
*
seem
to
be
iogic
0
or
iogic
1
signatures,
but
the difference
is
that
they have
activity at that point, (biinking
iamp)
(e.g.
oniy
iogic
0
or
iogic
1
between
start
and
stop).
7.
HOW
TO
USE THE
DOCUMENTATION AND THE TESTROM
This
service
manual should be used
in
combination with
the service
manual
of the
PM2521
.
The
user of the
fault-finding
procedure
in
the
PM2521
service
manual
will
be directed to
a certain
part
of the
PM2521
.
If
the fault-finding
procedure does not
solve the problem, then
select a
signature analysis
test
which
is
associated with the part of the
PM2521
.
Begin always with the
microcon;iputer, or
with the
inputs
of
the integrated circuits,
and
try
to find the faulty
node. Bear
in
mind
that
when
the
faulty
node
has been found,
more
than one
circuit
can cause the faulty
signature.
8.
FAULT-.F1NDING HINTS
The
first
thing to
do
is
to get
an
analysis of
what
is
wrong.
If
this
is
not possible
(e.g.
continuously —cal—),
get
the
PM2521
in
the
free
run mo'de by
breaking the bus system between
the
microcomputer and
the
ROMs.
This
is
done by removing
the
ROMs.
The microcomputer
is
now
forcing—
in
some
instruction that
will
cause
a
repeated increment of the address
lines.
So
at this
point the
microcomputer
is
scanning the
whole
address field.
With
START
and
STOP
lines
from
the signature analyser,
both connected to the
most
significant
address
bit
and
triggering
on
different edges,
a
measurement
will
be defined. Connecting the
CLOCK
line
of the
signature analyser to the
ALE
signal
of the
microcomputer and
selecting
the edge
at
which
the address
is
valid,
the input
probe
will
get
a
signature
at
every address
line.
By
touching the probe
in
every
test
to
a logic
1
level,
a characteristic signature
is
obtained. This
is
the
result
of
shifting
ones
(logic
1) in
for every cycle that
occurs while the
gate
is
open.
So
the characteristic
signature
can be used to diagnose
this
condition elsewhere.
The
logic
0
is
always
a
signature of
"0000".
Assume
there
are
no bad
signatures
in
the free-run
test,
then
the
TESTROM
can be placed
in
the
D1909
socket and
it is
possible
to
start
measuring with
test 0.
If
an incorrect part
can be located with the fault-finding
procedure
it is
recommended
to
start
with the
test
which
is
responsible for that fixed part of the
PM2521
.
To
do
this,
short
circuit
TP10
and TP1
1
for
a
short period-
9.
HOW TO ORDER THE
SIGNATURE ANALYSIS TESTROM AND
THE DOCUMENTATION
Under
ordering
number 5322 694 54013
the testrom
and
the
documentation can be ordered
from
Concern
Service.