Troubleshooting Guide
MD24 and MD30
5-5
#824820 - Revision A - December, 2013
C
PSU-DRAWER BOARD and RELAY TEST:
1. Disconnect power supply cord, and then remove outer case.
2. Open door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect leads to the primary of the MD transformer.
5. Ensure that these leads remain isolated from other components and oven
chassis by using insulation tape.
6. After insolating primary wires, re-connect the power supply cord.
Checking voltages on PSU-Drawer Board
1. Confirm voltage between pins CNA1 and CNA2 is 120 VAC. Check pins
CNC1 to CNC5 for 24 VDC. If 120 VAC and 24 VDC are NOT present then
check SW PSU-Drawer voltages and harness for breaks or shorts. If harness
is good replace the PSU-Drawer board.
Checking Relays for Oven Lamp/Common, MD Transformer, Stirrer motor,
and Fan motor.
1. If it you have correct voltages at the PSU-Drawer board and there is still no
operation of one of the above items, then perform a voltage check of RY1,
RY2, RY3 and RY4 Relays. These relays are operated by D.C. voltage.
Check voltage at relay coil with a D.C. voltmeter during microwave cooking
operation. D.C. voltage present indicates a defective relay. Replace PSU-
Drawer board. If No D.C. voltage present check diode connected to relay coil
is good. If diode is bad replace PSU-Drawer board. See Diode Test
Procedure “P.”
8. Disconnect power supply cord, and then remove outer case.
9. Open door and block it open.
10. Discharge high voltage capacitor.
11. Reconnect all leads removed from components during testing.
12. Re-install outer case.
13. Reconnect power supply cord after outer case is installed.
14. Run oven and check all function.
COMPONENT TESTPROCEDURE LETTER
RELAY SYMBOL OPERATIONAL VOLTAGE CONNECTED COMPONENTS
RY1 Approx. 26 VDC Oven lamp / Common
RY2 Approx. 25 VDC MD transformer
RY3 Approx. 26 VDC Stirrer motor
RY4 Approx. 26 VDC Fan motor
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