31
THE MICROWAVE SYSTEM
ISSUE RESOLUTION
F3 Fuse Blown 1. Fuse Blown: Replace F3 Fuse and determine why F3 Fuse opened.
: There are generally only three (3) faults that will cause the
F3 Fuse to open. They are as follows:
1. High Voltage Transformer Primary Winding shorted: Replace High
Voltage Transformer.
2. High Voltage Capacitor shorted or failing: Replace the High
Voltage Capacitor.
: A failing High Voltage Capacitor will typically cause the
High Voltage Transformer supplying power to the failing capacitor to
draw excessive current. This may open the F3 Fuse if the duration of
the excess current is long enough.
3. Monitor Circuit Fault: Verify operation of all Interlock Switches.
In addition, check the Fault Code Counter. If the Monitor Switch
opened prior to the Primary and Secondary Interlocks, the Control
would have recorded the occurrence. See page 21 and Chapter 6
(Cook Door) to trouble shoot the Interlocks.
Mag 1 or Mag 2 Not
Working or Food Not
Cooking Evenly
Determine which Magnetron is not oscillating by placing a clamp-on
Amp Meter on the Primary Winding of each High Voltage Transformer
and energizing the Microwave System.
1. Amp = 0. High Voltage Transformer not energizing.
Check K2 Relay and wiring going to suspect High Voltage Transformer.
o
K2 R
elay or wiring bad: R
eplace K2 R
elay and/or r
epair wiring.
o
K2 Relay OK: Check High Voltage Transformer. See the Table on
page 29 for r
esistance v
alues. R
eplace High Voltage Transformer
if defectiv
e.
2. Amps = 3 Amps on High Voltage Transformer. Magnetron is not
oscillating, but High Voltage Transformer is energizing.
o
Diodes failed: Replace Diodes.
o
Diodes OK: Replace defective Magnetron.
Magnetron Circuit
is Drawing E
xcessive
Current.
1. Measure resistance of High Voltage Capacitor(s).
R
esistance should star
t out in the megohm range and continue to
rise as the pr
obes are held on the Capacitor. If the resistance is low (less
than the megohm range), replace the Capacitor and visually check the
associated High Voltage Transformer Primary winding for signs of over
heating (winding is very dark and discolored). If Transformer Primary
Winding looks bad, replace it.
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