Power-Up Routine; Resistors; Coils And Transformers; Data Latches - Philips PM3055 Service Manual

14-10
V
-
Resistors.
Can
be
checked with an ohmmeter after having unsoldered one side of
the
resistor from the pcb.
Compare the measured value with the value
and tolerance indicated in the parts list.
- Coils and
transformers.
An ohmmeter can be used
for
tracing an open circuit. Shorted
or
partially shorted windings can be found by
checking the
waveform
responses when HF signals are passed through
the
circuit. Also an
inductance meter can be used.
-
Data
latches.
To measure
on inputs and outputs of data latches a
measuring
oscilloscope can be triggered by the
clock signal which
is
connected
to the
clock input of the
data latch.
This measurement can only be made in this
way when there
is
an
acceptable repetition time of the clock signal.
A too low clock pulse
repetition
time results in a
low intensity
of the
trace on the
measuring oscilloscope screen.
The outputs can easily be checked by
a
voltmeter
or
oscilloscope,
14.5.3
Power-up routine
Every
time the instrument
is
switched-on the
following initialisation
program
is
executed:
- Resetting the IlC-bus.
- Resetting D2603 (OQ 0200)
— Determinig the
SLAVE-address of D2603.
-
Checking if
Service routine
is
required
(if yes the
program will
^
continue with
the
service routine)
.
- Checking the
"WATCH-DOG" on A7 (if HIGH, all
relevant LCD-segments
will be lighting for about
1
sec),
-
Eventually initialisation
of the lEEE-option,
If during the program-run a
circuit
is
found
to
be faulty, the program
stops. It is
recommended
to
switch-off
and after
a
few seconds
switch-on
again. This
will reset the
micro-computer controlled system
automatically.
If
the
instrument goes in
the same faulty
situation
again, the following procedure indicates
how
to
handle.
If no
faulure
is
found, all
relevant LCD-segments will be lighting
for
about one
second. After this the normal program
is
executed,
PROCEDURE
:
Check the
SDA and SCL lines^
after haved switched-on. On the SCL a
clock-pulse must
be present,
while the SDA gives the
data-information
(looks like
a
random pulse).
If one of these signals
is
not present,
you can localize on what unit the fault exists. This can be
done by
first unplug connector X1009 or X2001 on resp. A1
and A2. To localize
what serial-parallel
conversion
IC is
defective, you can disconnect
the solder joint in the SDA and SCL
print track lead
to
that IC.
The
following IG's can
disconnected in this way:
DlOOl, DllOl, D2602,
D2603,
D40t)l,
D4002, D4401.
When
the
instrument restarts every time again, this means the WATCHDOG
is
initiating
the.
main program
(see also
section 10.1.4), the
watchdog
can be disabled. This can be done
by means
of the solder joint jumper
on the rear of the front unit p.c.b. (near X7001).
When disabled, pin
13 of
the
microcomputer
is
set
to a low level.