GE JT930 Service Manual page 2

MICROWAVE (CONT.)
f. Safety Interlocks
The microwave interlock system has a left and a right interlock assembly:
Left Interlock Switch Assembly: Door sense switch (NO) and secondary
interlock switch (NO) with 2–two position connector with black and brown
wire outputs.
Right Interlock Switch Assembly: Interlock monitor switch (NC) and
primary interlock switch (NO) with one 4-position connector with red and
black wire outputs.
NOTE: Perform microwave leakage test when replacing or adjusting
interlock switches or door latch.
NOTE: ENSURE THAT POWER IS OFF FOR THE BELOW TESTS.
Testing the Primary & Secondary Interlock Switches
• Disconnect power and remove oven partially from wall. Remove front
part of top cover. Remove interlock switch cover on side of oven.
• Remove interlock switch leads to isolate the switch.
• Check for continuity of switch with door open and door closed:
open = ∞Ω and closed = 0Ω.
Testing the Interlock Monitor Switch
• Remove interlock monitor switch leads to isolate the switch.
• Check for continuity of switch with door open and door closed:
open = 0Ω and closed = ∞Ω.
Testing the Fuse
• Check the 20-amp fuse for continuity and proper size. When replacing,
do not use any other fuse type, size or rating except 250V/20A
Type 3AB ceramic cartridge fuse.
• WARNING: Primary interlock switch and interlock monitor switch
(Right Interlock Switch Assembly) must be replaced when 20 amp fuse
is blown due to operation of interlock monitor switch.
Replacing Interlock
• Replace interlock switch assembly when 20A fuse is blown due to
operation of the monitor switch.
DOOR SWITCHES
Oven Door Sense Switch
The oven door sense switch is located in the left interlock assembly.
Proper operation of the door sense switch is required for proper operation
of the oven light, microwave system, convection fan and the door lock.
To check the door sense switch:
1. Enter SERVICE MODE (see SERVICE MODE section).
2. Select DOOR POSITION option and observe the display as the door is
opened and closed.
3. If the state (open/closed) does not change on the display, turn off power
and check wiring and switch with ohmmeter.
229C4059P444-1
THERMAL SWITCHES
Magnetron TCO – This self-resetting thermal switch is located on top of the
magnetron housing and is wired in series with L1 to the main power board.
This limit switch will open when the temperature on the magnetron reaches
320°F, removing power to the oven, and closes when it cools below 140°F,
restoring power to the oven. Check for proper magnetron cooling fan
operation (blockage, blades not turning).
One-Shot TCO – This thermal switch is located on the rear of the oven
behind the center cover and is wired in series with L2 from the conduit. This
limit switch is a non-resettable device and will open at 302°F, indicating a
thermal runaway condition. If tripped, the oven must be removed from
installation in order for the one-shot TCO to be replaced. Cause of
overheating should be determined when replacing the device.
Sail Switches – The left and right sail switches are normally open limit
switches located at the rear of the component compartment in front of the
cooling fans. These switches monitor the presence of the airstream from the
fans. If either fan malfunctions, the applicable sail switch will open and will
open relay R1 and R2, which disables power to the microwave HVT and
cooking elements.
SPECIAL FUNCTIONS
These are options that change the behavior of the control for a specific
reason and could confuse the consumer if accidentally entered.
• Control Lockout – Press the 7 & 8 keypads at the same time for 3
seconds. The text display will show "Control Is Locked." To unlock the
control, press the 7 & 8 keypads for 3 seconds. Display will return to the
standard Main Menu.
• Sabbath Mode – This feature disables all but the bake and timed bake
modes. Additionally, the display does not show the temperature and sound
is disabled. The element and oven icons will light to indicate that the oven
is operating and all time functions will remain displayed and active. Sabbath
Mode is accessed through the Features menus. To turn this feature on,
press the keypad next to SABBATH. To turn this feature off, hold the BACK
keypad for 3 seconds. The control will return to the Features menu where
SABBATH was originally selected. NOTE: This feature remains active even
after loss of power to the oven. The only way to exit Sabbath is to hold the
BACK keypad for 3 seconds.
• Sales Mode – Becomes active upon powering up with oven L1-L2 = 120VAC
with special power cord (L1 of oven connected to L of 120V source, L2 and
N of oven connected to N of 120V source). This mode is NOT accessible
on 240V/208V power supply. Must remove 120V power source and apply
240V/208V to exit Sales mode.
• Time of Day Settings – Time of Day Settings are accessible through the
Settings menu. All cooking and cleaning related timed functions (TimedBake,
DelayBake, 2Temps [on some models] and DelayClean) are accessible
through their related cooking or cleaning function if available. The kitchen
timer is a button on the control panel under the time/temperature display.
• Oven Calibration – Oven calibration offset can be adjusted for bake mode
by the consumer by accessing the SETTINGS menu. Press SETTINGS,
then MORE, then MORE then ±temp. Select INCREASE or DECREASE
to change the cooking temperature in 1° increments up to ±35°F.
NOTE: Oven calibration offset can also be accessed through the SERVICE
MODE menu. Enter SERVICE MODE, then press NEXT, then NEXT then
OFFSET.
ERC FAILURE CODES
Failure
Code Meaning Corrections
F0 Keyboard error Perform a key panel test, making
sure to test EVERY pin combination
for possible shorts. If there are no
shorts or signs of delamination, the
problem is probably with the control.
Enter SERVICE MODE, then NEXT,
then NEXT then DISPLAY (ON/OFF).
Press Clear/Off key to reset. If
working properly, enter BACK, then
KEYS and test key functions.
F2 Temperature Runaway— • Check for welded element relay
oven temperature is contacts.
above 630°F unlocked
• Check airflow to rear of unit.
or 930°F locked
F3 Open sensor/RTD • Disconnect power to unit and then
disconnect oven sensor harness
from control. Make sure sensor
resistance (white leads) are
–1080Ω at room temperature
with 2Ω/° change. (Pins 1 and 2
of the 12 position connector for
upper wall oven, and pins 11 and
12 for lower wall oven found on
the MLB J7 harness).
F4 Shorted sensor/RTD • Verify resistance. See F3 diagnosis.
• Measure each sensor lead from
connector block to ground. If
shorted, look for pinched or cut
wire in sensor circuit.
• Check connector terminals. Look
for deformity or corrosion on terminals.
Repair or replace if necessary.
• If all above is OK, then replace
the main logic board.
F5 Control Sensor Circuit— • Check sensor circuit for intermittent
Supervisor Error high resistance. See F3 diagnosis.
• Press Clear/Off and reprogram
control. If code reappears, replace
control.
DO NOT REPLACE LOCK MOTOR.
This tests:
a) Redundant measurement
circuits on Main board do not
match closely enough.
b) Door latch motor (and microwave
and convection fan) is not
disabled by temperature
measurement circuits at the
proper temperature.
• Replace the main logic board
F8 EEPROM data error If repeated, replace the main logic board.
FC Door Latch Error • Problem with door lock circuit such
as pinched wires between control
and door lock switches on
motorized lock circuits.
• Check wiring and test operation
of switches.
• Error occurs when both lock and
unlock switches are closed at the
same time.
Fd Display Error • Check main reconfigurable display
connections.
• Replace main reconfigurable display.
• Replace main logic board if error
does not clear.
Note: When trying to enter temperatures lower than 170°F or greater than
550°F in any mode, or lower than 90°F or greater than 120°F in DEHYDRATE
mode (some models only), display will momentarily show "Err" and then the
default minimum or maximum temperature will be entered.