Technician Service Guide 33367B
9
If the measured AC voltage indicates the
transformer has failed, indicated by significantly
lower voltage readings, replace the transformer with
the replacement service part specified on the parts
list for the model of charger being serviced.
Charger
Nameplate
DC Voltage
No Load
Output Coil
AC Voltage*
No Load
Auxiliary Coil
AC Voltage
12
28-44
24
56-90
36
90-126
48
120-168
24-32
Note: The voltage readings are approximate and
transformer failure is indicated when the
measured AC voltages are SIGNIFICANTLY
LOWER than the listed values.
(*) The wide AC voltage range is the result of
various AC line voltages that many charger
models have been designed to operate on.
Table 2
If it should become necessary to replace a terminal
on one of the transformer leads, the new terminal
must be crimped AND soldered.
SECTION 4 – SCR TESTING
The feedback control design of the charger makes it
possible for one SCR in the SCR assembly to not
function and the charger to still have some output.
This condition can be detected by noting the
temperature of the separate SCRs and replacing the
complete assembly if one of the SCRs feels cold
and the other hot. This condition may also suggest
it’s presence by continual melting of the DC fuse,
see
Section 6 – Charger DC Circuit Breaker
Trips/Fuse Blows
for additional information.
An SCR can fail in a shorted or open mode. Shorted
SCRs can be detected by measuring the resistance
between the legs of the SCR with an ohm-meter. An
SCR that is shorted Anode to Cathode will cause the
DC circuit breaker to trip or fuse to blow, see
Section 6 – Charger DC Circuit Breaker
Trips/Fuse Blows
for more information. An SCR
with a shorted anode to gate can be detected by
measuring the resistance between the anode to
gate. 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.
Locate the in-line bullet connectors on the brown
leads (gate) of the SCRs and disconnect, see figure
6.
Figure 6
Using an ohm-meter, measure the resistance
between between the brown gate lead of the SCR
and the heatsink plate (SCR anode). Test each
SCR separately. Connect the positive (+) lead of the
ohm-meter to the heatsink plate (anode) of one
SCR. Connect the negative (-) lead of the ohm-
meter to the brown gate lead for that same SCR.
The resistance for a good SCR should be about 20
megohms. Reverse the leads of the ohm-meter and
test the SCR again. Resistance for a good SCR
should be in the megohms.
The resistance of a failed SCR, regardless of ohm-
meter polarity, will be about 50 ohms.
If an SCR with a shorted anode to gate is located,
the electronic timer has been damaged and must be
repaired or replaced with the SCR assembly.
WARNING: ALWAYS TEST SCRs BEFORE
REPLACING AN ELECTRONIC TIMER. DAMAGE
AND SUBSEQUENT FAILURE WILL OCCUR TO
ALL ELECTRONIC TIMERS INSTALLED IN A
CHARGER THAT CONTAINS A SHORTED
ANODE TO GATE SCR, IF CONNECTED TO AC
POWER.
DANGER: HAZARD OF ELECTRIC SHOCK!
THE FOLLOWING TEST REQUIRES THE
CHARGER TO BE CONNECTED TO A LIVE AC
OUTLET. FOLLOW ALL ELECTRICAL SAFETY
PRECAUTIONS TO AVOID ELECTRIC SHOCK!
