Frigidaire GLBM188HB, Service Manual

Page: 10 / 47

Page 10
GLBM188HB
6 – 1
GLBM188HB Service Manual
CHAPTER 6.
OPERATION
[1] DESCRIPTION OF OPERATING SEQUENCE
The following is a description of component functions during oven operation.
1. OFF CONDITION
Closing the door activates the door sensing switch and secondary
interlock switch. (In this condition, the monitor switch contacts are
opened.)
When oven is plugged in, 120 volts A.C. is supplied to the control unit.
(Figure O-1).
1. The display will show “ENJOY YOUR OVEN PRESS CLEAR”.
To set any program or set the clock, you must first touch the Clear
Off pad. The display will clear, and “ : " will appear
2. COOKING CONDITION
Program desired cooking time touching the NUMBER pads. When the
START pad is touched, the following operations occur:
1. The contacts of relays are closed and components connected to
the relays are turned on as follows.
(For details, refer to Figure O-2)
2. 120 volts A.C. is supplied to the primary winding of the power trans-
former and is converted to about 3.3 volts A.C. output on the fila-
ment winding, and approximately 2000 volts A.C. on the high
voltage winding.
3. The filament winding voltage heats the magnetron filament and the
H.V. winding voltage is sent to a voltage doubler circuit.
4. The microwave energy produced by the magnetron is channelled
through the waveguide into the cavity feed box, and then into the
cavity where the food is placed to be cooked.
5. Upon completion of the cooking time, the power transformer, oven
lamp, etc. are turned off, and the generation of microwave energy
is stopped. The oven will revert to the OFF condition.
6. When the door is opened during a cook cycle, monitor switch, door
sensing switch, secondary interlock switch, and primary interlock
relay are activated with the following results. The circuits to the
antenna motor, the cooling fan motor, the turntable motor, and the
high voltage components are de-energized, and the digital read-out
displays the time still remaining in the cook cycle when the door
was opened.
7. The monitor switch is electrically monitoring the operation of the
secondary interlock switch and door sensing switch is mechanically
associated with the door so that it will function in the following
sequence.
1) When the door opens from a closed position, the primary inter-
lock relay, door sensing switch and secondary interlock switch
open their contacts, and then the monitor switch contacts close.
2) When the door is closed from the open position, the monitor
switch contacts open first. Then the contacts of the secondary
interlock switch and door sensing switch close. And contacts of
the relay (RY1) open.
If the secondary interlock switch and primary interlock relay (RY2)
fail with the contacts closed when the door is opened, the closing of
the monitor switch contacts will form a short circuit through the
monitor fuse, secondary interlock switch, relay (RY1) and primary
interlock relay (RY2), causing the monitor fuse to blow.
3. POWER LEVEL P-0 to P-90 COOKING
When Variable Cooking Power is programmed, the 120 volts A.C. is
supplied to the power transformer intermittently through the contacts of
relay (RY2) which is operated by the control unit within an interval sec-
ond time base. Microwave power operation is as follows:
NOTE: The ON/OFF time ratio does not correspond with the percent-
age of microwave power, because Approx. 2 seconds are
needed for heating of the magnetron filament.
4. POWER OUTPUT REDUCTION
If the oven is set for over 40 minutes at 80%, 90% or 100% power
level, after the first 40 minutes the power level will automatically adjust
itself to 70% power to avoid overcooking.
5. VENTILATION METHODS HOT AIR EXHAUST
1. VERTICAL VENTING
For this venting method, hot air rising from the conventional range
below is drawn in by the hood fan motor through the grease filters
at the right and left sides of the base cover, up through the right and
left sides of the oven cavity, then discharged vertically at rear cen-
ter top of the oven, into the customer's vent system.
RELAY CONNECTED COMPONENTS
RY1 Oven lamp / Fan motor / Antenna motor
RY2 Power transformer
RY3 Turntable motor
VARI-MODE ON TIME OFF TIME
100% power 32 sec. 0 sec.
Approx. 90% power 30 sec. 2 sec.
Approx. 80% power 26 sec. 6 sec.
Approx. 70% power 24 sec. 8 sec.
Approx. 60% power 22 sec. 10 sec.
Approx. 50% power 18 sec. 14 sec.
Approx. 40% power 16 sec. 16 sec.
Approx. 30% power 12 sec. 20 sec.
Approx. 20% power 8 sec. 24 sec.
Approx. 10% power 6 sec. 26 sec.
0% power 0 sec. 32 sec.
HOOD FANMOTOR
AIR FLOW
HOOD
INTAKE
DUCT
TO DUCT
TO DUCT
GREASE
FILTER