Chamberlain JDC Manual page 46

Troubleshooting (continued)
Symptom
Powerhead main
board is off
(no LEDs are lit or
blinking)
(continued)
Possible Causes Diagnosis
Faulty EMI filter Verify EMI filter board:
board Perform this test only after first
verifying input AC voltage.
Measure AC voltage at EMI filter
board output. Measure from brown
wire to blue wire. [todo: check wire
colors for 480V] Verify voltage is
within specifications.
Faulty Transformer Verify Transformer:
Perform this test only after first
verifying the EMI filter board.
Disconnect transformer output
winding from rectifier(s) and
measure the AC voltage across
transformer output winding.
Voltage should be between 22
and 35 volts AC. If voltage is out of
range, see resolution.
Faulty wiring or Inspect all connections and wiring
connections from EMI filter board, transformer,
rectifiers, and DC IN terminals on
the main board. Ensure there are no
loose connections, cut wires, broken
insulation, etc.
Verify wiring matches wiring
diagram.
Faulty Rectifier Verify Rectifier:
If the transformer and all wiring is
verified but DC voltage is still not
present at the main board DC IN
terminals, the rectifiers are most
likely faulty.
If an electrical meter with a diode
test function is available, each of
the 4 diodes internal to the bridge
rectifiers may be checked using the
diode check functionality:
1) check each diode in the forward
direction and verify they conduct
with ~ 1V drop or less
2) check each diode in the reverse
direction and verify they do not
conduct (meter will read the same as
disconnected leads)
Short or overload Turn off power and disconnect
in device batteries from main board.
connected to main Disconnect all cabling from main
board board except for main power.
Restore power and verify LEDs light.
Reconnect wiring to main board one
device at a time testing to see if any
device causes the main board to fail
to light LEDs.
46
Resolution
If input voltage is within
specification but output voltage is
outside specifications or is absent,
replace the EMI filter board.
If voltage is too high or too low,
check that 120V/240V input voltage
selection is correct.
If voltage is absent: transformer has
thermal protection to automatically
disconnect input voltage if the
transformer overheats. Allow
transformer to cool if it is hot, and
then re-test.
If transformer is cool and voltage is
still absent, replace the transformer.
Correct any issues found with wiring
or connections.
Replace faulty rectifier(s).
Rectifier mounting screws must
be tight enough to ensure good
thermal contact with the chassis
through the thermal interface
pad. However, the rectifier screw
must not be too tight or it could be
damaged. [torque spec here, even?]
Interface between the rectifier and
the chassis should be clean of any
foreign substances before a new
rectifier is installed.
If any device is found to cause an
issue, the device may be faulty and
should be repaired or replaced as
necessary.