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ISSUE RESOLUTION
F3: Magnetron
Current Low (cont.)
WARNING: Never try to check the secondary voltages of the High
Voltage Transformers.
With the top cover removed, safe access to the three (if US oven)/two (if
International oven) terminals on the top of the transformers is available.
NORTH AMERICA - Place the AC voltmeter across terminals 1+3. Press and
hold the
MGTRON soft key. Voltage present should be 240 +/- 10%.
INTERNATIONAL - Place the AC voltmeter across terminals 1+2. Press and
hold the
MGTRON soft key. Voltage present should be 230 +/- 10%.
JAPAN - Place the AC voltmeter across terminals 1+2. Press and hold the
MGTRON soft key. Voltage present should be 200 +/- 10%.
If voltage is present on both high-voltage transformers, perform the compo-
nent troubleshooting steps in the previous pages of this section.
If voltage is not present, check for 24VDC control voltage from I/O board
to the K2 relay. Access voltage reading from the "QC3" connection located
at the bottom right side of the wiring harness. When the
MGTRON key is
pressed and held, 24VDC should be present on pins 1+5. Reference the
schematics (pages 55-63) for physical location of pins on QC3 connector.
If voltage is present at the connector, inspect the K2 relay and the wiring.
Unplug the oven and replace relay if necessary.
If voltage is not present at connector, check wiring connections at the con-
trol board on the 40-pin connector. Also check the wiring between the two
connectors. Unplug the oven and replace control board if necessary.
F3 Fuse Blown Replace the F3 fuse and determine why F3 fuse opened.
Generally, the F3 fuse opens for one of three reasons:
a. HV transformer primary winding shorted: Unplug the oven and
replace the HV transformer. Follow troubleshooting on page 33 to
determine cause of failure.
b. HV capacitor shorted or failing: follow troubleshooting on page 33.
If necessary, unplug the oven and replace the HV capacitor.
NOTE: A failing HV capacitor will typically cause the HV
transformer that supplies power to the failing capacitor to draw
excessive current, which may open the F3 fuse.
THE MICROWAVE SYSTEM
35