Model #KEMS378SBL00, this built-in oven and microwave combination started to display an F1 E3 error message on the microwave control panel shortly after the unit was installed. The oven portion still worked correctly according to the customer, so I started my trouble shooting with the microwave portion of the circuit. A little help from the tech sheet and I was ready to pull the unit from the cabinet.
This particular oven and microwave combination is a new design that is a bit of a departure from the usual platform that has been used by Kitchenaid for some time. Because of the complex nature of this unit and the electronics evolved, most everything that will need to be tested or replaced is mounted behind the display or on the left side of the unit. This makes all but a few of the components out of reach unless the unit is removed from the cabinet for servicing.
The F1 E3 error message indicates there is a problem with the microwave appliance manager board. This unit has two manager boards, one for the oven and the other for the microwave. Each of these boards communicates with the display and logic boards mounted to the front of the control panel. If there is a loss of communication between the control and manager boards, the appropriate error message will be logged and displayed. Because this error is for the microwave board only, I took a look at the circuit diagram from the tech sheet (it's under the top panel on the right side) to see where to start making my tests.
The first place I looked was to verify voltage to the manager board. If the board has no power, well it isn't going to be working and thus not talking with the logic board. Checking for voltage using my meter, I found no voltage at the input from the L1 side of the circuit. There are two fuses on this circuit. One is the monitor fuse (located by the manager board) used to cut power to the unit should there be a problem with the interlock switches. The second is the line fuse (located on the left side by the oven manager board) used to protect the unit from a voltage spike from the house electrical connection. Checking both fuses for voltage, I found nothing on the monitor fuse, but did find voltage on the L1 side of the line fuse. This left the filter board right in the middle.
Filter boards (this unit has two) are used to reduce noise coming from the electrical connection that may cause damage or interference to the units logic boards. As more appliances are adding logic boards that use low voltage DC cables for communications, these filter are becoming more of a necessity to ensure proper operation.
From the voltage checks on the fuses, it looked like I had voltage going into the L1 filter board, but nothing coming out. Locating the board to the left of the microwave manager board I did voltage checks at the board itself when I located the problem. A capacitor attached to the filter board had basically blown up and aside from leaving a burn mark, it also opened the L1 circuit to the manager board. With no power to the board, the microwave logic board lost communications and displayed the F1 E3 error. Because both fuses checked out OK, I figured the filter board was the sole fault for this error. And once I replaced the filter board, the error was no longer displaying, and the microwave even worked.