Microwave Drop-down Door Series
Microwave Drop-down Door Series
Troubleshooting
Troubleshooting
4-6
#826151 - Revision A - March, 2016
Perform 3E Checks (page 4-2)1
Isolate the HV capacitor from the HV circuit2
Discharge the HV capacitor3
Measure the resistance of the HV capacitor4
a. Analog meters will show continuity for a short time, then a steady rising
resistance
b. Digital meter on resistance shows continuity, then jumps to about 10
MOhms
c. Digital meter on capacitance shows the rating of the capacitor ± 20%
Check for infinite resistance from each HV capacitor terminal to the HV5
capacitor case
If the HV capacitor shows infinite resistance for 4 a. and 4 b., and does not6
start at a low resistance first - the HV capacitor is bad
Perform 4R Checks (4-2)7
Perform 3E Checks (page 4-2)1
Remove wires from switch terminals2
COM to NO terminals will show zero resistance when the plunger is3
depressed and infinite resistance when plunger is released
COM to NC terminals will show infinite resistance when the plunger is4
depressed and zero resistance when plunger is released
Perform 4R Checks (4-2)5
Perform 3E Checks (page 4-2)1
Disconnect the wires from the TCO terminals2
Measure the resistance between the terminals3
Below 145° C (293° F) resistance is close to zero4
Infinite resistance means the TCO has been exposed to temperatures5
above 145° C (293° F) or has failed. The TCO is not resettable.
a. The magnetron TCO reading infinite resistance could be caused by the
magnetron over heating from restricted ventilation, or cooling fan failure.
b. The cavity TCO reading infinite resistance could be caused by the cavity
over heating from running without a load or a fire.
Replace a TCO that is reading infinite resistance6
Perform 4R Checks (4-2)7
TEST
PROCEDURE
COMPONENT TEST
HIGH VOLTAGE CAPACITOR
TEST
MICROWAVE SWITCH TEST
THERMAL CUT OUT (TCO)
TEST
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