H ELECTRICAL SYSTEM
ZENER
DIODE
TEST
PROCEDURE
(Procedure
forTesting on the Machine)
The
t~st
procedure given below
can
be
used
when
it
is
required
to
check
the
performance
of the Zener Diode type
ZD715
whilst
it
is
in
position on
the
machine.
It
is
essential
that
the
battery
is
in
a fully
charged
state,
otherwise
the
tests
below
will
not be accurate.
If
in
doubt,
substitute
a battery
that
is fully
charged.
Good
quality moving coil
meters
should
be
used
when
testing. The
voltmeter
should
have a scale
0-18,
and
the
ammeter
0-5
amps
min. The
test
procedure
is
as
follows:-
(A)
Disconnect the cable from
the
Zener
Diode
and
connect
ammeter
(in
series)
between
the diode Lucar terminal
and
cable
previously disconnected. The
ammeter
red
or
positive lead
must
connect
to the diode Lucarterminal.
(8)
Connect
voltmeter
across
Zener
Diode
and
heat
sink. The red
or
positive lead
must
connect
to
the
heat
sink which
is
earthed
to
the
frame of
the
machine by it
fixing bolts and a
separate
earth
lead. The
black lead connects to the
Zener
Diode
Lucar terminal.
(C)
Start
the engine, ensure
that
all
the
lights
are
off,
and gradually increase
engine
speed
while
at
the
same
time
observing
both meters:-
(I)
The series connected
ammeter
must
indicate zero amps, up to
12.75
volts,
which will be indicated on
the
shunt
connected
voltmeter
as
engine
speed
is
slo'(Vly
increased.
(i1)
Increase engine
speed
still further, until
Zener
current indicated on
ammeter
is
2.0
amp. At this value the Zener
voltage
should be within 14.2 voits to
15.8
volts,
(gold finished Zener)
or
14.7 volts
to
15.8
volts (silver).
TEST CONCLUSIONS:-
If
the
ammeter·
in
test
(i)
registers any
current
at
all
before the voltmeter
indicates
12.75
volts,
then
a replacement
Zener
Diode
must
be fitted.
If
test
(I)
is
satisfactory
but
in
test
(ii)
a
highervoltage than
that
stated
is
registered
on
the
voltmeter, before the
ammeter
indicates
2.0
amp,
then
a replacement
Zener
Diode
must
be fitted.
-
f=:=========================:l
AI48
Fig.
H12. Showing
ammeter
and
voltmeter
connections far
test
purposes
H14
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