Posting this to help anyone who might have the same problem. This describes the situation I had and the steps I took, your situation could be different. Also, proceed at your own risk.
Problem:
Maytag Neptune Washer (model MAH3000AWW from 1999) suddenly stopped. When Start button is pushed "ON" light comes on and it starts filling, then the machine shuts off after about 5 seconds. Found that if the timer is turned to a SPIN setting and button is held, the pump will run and drain the tub, but that is all.
Diagnosis and Repair:
BE SURE TO WORK SAFELY – UNPLUG THE WASHER WHENEVER OPENING THE CABINET, DISCONNECTING OR CONNECTING ANY WIRES, OR HANDLING ANY COMPONENTS. STAY AWAY FROM ENERGIZED COMPONENTS, AND FOLLOW ALL SAFETY RULES. IF UNSURE ALWAYS CHECK FOR LIVE VOLAGE USING A MULTIMETER.
Disconnected the power to the washer. Took off the front panel (fairly straightforward, instructions can be found via Google). Removed screw holding down the clear flexible plastic drip shield and flipped it out of the way and examined the motor control board (mounted at the front right of the cabinet). The 10A glass fuse is blown (shows black marks). Checked continuity across the fuse and verified it is blown. Also checked to make sure power (110 V AC) is coming to the Line (L) (black wire) and Neutral (N) (white wire) terminals at the top right of the board (see picture, just below the green wire at the top right which is the ground wire)– have to make sure washer door is closed and Start/Stop is pressed on the control panel to do this check.
The repair manual says if the fuse is blown to replace the motor control board and wiring harness. But first want to see if just replacing the fuse might work.
Fuse is 250V 10 amp glass fast acting. Attached alligator clips to ends of a fuse holder (automotive plastic in-line fuse holder) with the fuse in it and attached the clips to each end of the fuse on the board, to see if board would work. Removed JP4 on the motor control board (in attached photo it is the one on the right side with 2 white, a yellow, a blue and a red wire, and is labelled JP4 on the board), set the timer to the delay start range, plugged in the washer and pressed start. The motor is supposed to go into a slow (about 50 RPM) tumble if the board is OK. (The washer door must be closed). The fuse blew immediately.
Next, tried to disconnect 1 phase of the motor at a time. The motor is a DC reluctance 3 phase motor. The 3 phases have 3 sets of wires along the lower end of the board going to them from the motor control board:
Phase A – plus is black wire, minus is blue wire
Phase B – plus is red wire, minus is white wire
Phase C – Plus is yellow, minus is orange
If you look closely on the board the wire colors and the phase names and plus/minus are printed near the connectors.
Disconnected Phase A, left phases B & C connected – fuse blew
Disconnected Phase B, left phases A & C connected – fuse blew
Disconnected Phase C, left phases A & B connected – fuse did not blow, motor went into slow tumble.
(Unplug washer while changing connected phases. Also, to get better access to the terminals and connectors need to remove the 2 screws holding the plastic mounting of the board to the washer body and pull the whole board assembly forward. You might also have to remove the diagonal brace on the right side of the body which hinders access to the board.)
So, phase C is causing the problem, but is it a bad board or bad motor? To decide, again unplugged washer and checked resistance between the 2 wires of each motor phase, and between all 6 wires and ground. Each phase was identical – winding resistance about 2.7 ohms in each phase, and no short circuits to ground on any wire. Also, the motor and drum turn freely and thus not likely motor is drawing a heavy current because of a jam.
So, while not 100% definitive, most likely culprit is the board. Disconnected all the connectors and removed the board (need to remove the P clip holding the wires to the board). There are 3 sets of MOSFETs along the bottom of the board. Each set of 2 MOSFETs has a heat sink screwed on top and each set feeds one phase. Checked resistance between gate and drain for all 6 MOSFETs. For the 2 that feed Phase C (rightmost) there was a short, while the other 4 MOSFETs showed a high resistance. The MOSFETs are IRF644 (printed on each, visible once heatsink is removed) and by checking the data sheets via Google determined which leg is drain, gate and source. If the metal tab is toward you then leftmost leg is Source, middle one is Drain (also connected to the tab) and the rightmost one is Gate. You can also Google/YouTube for other tests, such as to determine if the MOSFET is off when no voltage is connected to the Gate and that it will turn on when the gate is energized. BE CAREFUL ABOUT ELECTROSTATIC DISCHARGE WHILE HANDLING THE BOARD – DISCHARGE YOURSELF TO A GOOD METALLIC GROUND BEFORE TOUCHING ANY COMPONENTS.
So, the board is definitely bad. Only question is why did it go bad – did a bad motor cause the 2 MOSFETs to blow? The above motor tests indicate that the motor is most probably OK, so only way to be sure is to repair the board (replace the fuse and the 2 MOSFETs) or replace it. Chose to just buy a used replacement board on ******** (make sure part number matches that of the existing board, it has to be compatible with your motor), installed it back in the washer and all is OK – the motor spins and the washer goes through all cycles normally.
boxer attached the following image(s):
