Technician Service Guide 33367B
10
The SCRs may be electrically tested for an open
condition by turning them on one at a time manually
while the charger is energized. To do so, first
disconnect the charger AC power plug from the
outlet and the DC output cord from the equipment
charging receptacle. Remove the charger’s cover
and carefully remove the control cable edge
connector from the electronic timer.
Before testing the SCRs, inspect and test for
continuity the gate lead of each SCR. (Note: The
SCRs in some charger designs are soldered directly
into the printed circuit board and will not have gate
leads.) First, inspect the contacts in the edge
connector for distortion, corrosion or any condition
that would prevent electrical contact with the pads
on the electronic timer. Measure the continuity of
each BROWN gate lead by placing one test probe
from the continuity meter on the brown gate lead at
the SCR. Place the remaining test probe on the
appropriate contact in the electronic timer edge
connector, pins 1 and 2 on the service wiring
diagram. Repeat the same test on the remaining
SCR gate lead. If no continuity is measured on the
gate lead(s), rework or replace the edge connector,
in-line bullet connector and/or wiring, as needed.
Each SCR may be turned on manually by
connecting a 3 volt battery to the SCR. (Note: Some
SCRs may require only 1.5 volts DC to forward
bias.) Connect the AC power plug to a live outlet,
connect the DC output plug to a fully charged battery
pack and set the power switch to AUTO. Connect
the negative (-) end of the battery to the output side
of the SCR (cathode) by attaching to the shunt, test
point E on the service wiring diagram, or the positive
DC cordset connection. Momentarily touch the lead
from the positive (+) end of the battery to the gate
lead of each SCR in the electronic timer edge
conenctor, pins 1 & 2 on the service wiring diagram.
See figure 7. Do not continue this for more than a
few seconds as it is possible to damage the SCRs
and charger.
Figure 7
If the SCRs are good, the charger’s ammeter will
indicate current flow when each SCR gate lead is
touched by the positive (+) end of the battery. For
chargers without an ammeter an in-line ammeter
may be used in the DC charging circuit to test for
current flow or a DC voltmeter may be used to test
for momentary battery voltage increase.
If the ammeter does not indicate current flow for
each SCR, the SCR not causing ammeter deflection
has failed and the SCR assembly must be replaced.
SECTION 5 – CHARGER AC CIRCUIT BREAKER
TRIPS/FUSE BLOWS
Before proceeding, verify the rating of the blown
fuse is correct for the model of charger being
serviced. If the value is lower than specified for the
charger being serviced, install a fuse of correct size
and recheck charger operation. If the AC protection
device is a circuit breaker, the quickest and most
accurate way to eliminate the possibility of a faulty
breaker is to replace the breaker with a known good
one.
There are two modes of failure, instantaneous and
delayed blowing of the AC protection device. If the
AC protection device allows the charger to operate
for a period of time before blowing, this is usually the
result of gradual heating of the protection device.
Inspect the connections to the circuit breaker/fuse
for signs of heat caused by a loose connection,
corrosion, physical damage or otherwise.
If the AC protection device itself passes inspection,
the most likely cause is a failed SCR. The failure of
one SCR will force the remaining SCR to try and
produce the charger’s full output. This results in a
high current draw on the portion of the input AC sine
wave that the remaining good SCR is rectifying. The
higher AC current draw eventually causes enough
heating of the AC protection device to cause it to
blow. See
Section 4 – SCR Testing.
Instantaneous blowing of the AC protection device
indicates a direct short. Refer to the service wiring
diagram, the only component following the AC
protection device is the transformer. If the AC
protection device itself passes testing and
inspection, replace the transformer and retest. If the
wiring diagram for the specific model of charger
being serviced shows any other component(s)
between the AC protection device and the
transformer, isolate each component and test with a
continuity meter for a shorted condition before
replacing the transformer.
DANGER: REPLACE THE FUSE OR FUSE
ASSEMBLY ONLY WITH THE CORRECT FUSE
OR FUSE ASSEMBLY. FIRE, PROPERTY
DAMAGE, AND PERSONAL INJURY CAN
