Author Topic: Fused 24V trace on Machine Control Board  (Read 1453 times)

Offline dpecorella

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Fused 24V trace on Machine Control Board
« on: May 06, 2009, 10:21:59 AM »
The machine is about 7 years old and itís been a bear to maintain over the past 2 years; at least 4 service calls in that time.  

My new issue is that the washer wonít start.  When I opened the unit and inspected the machine control board, I found black spot on the backside trace between Pin 1 on CONN P3 and Pin 3 on CONN P4; it was fused open.  The wiring diagram indicates that this is a 24V bus line.  With power on I metered the pins and there was 120 AC where the 24V DC should have been.   I inspected the motor control board, no obvious problems, fuse in tact.  The wax motor and R11/Q6 are also perfect.  

Anyway I spent my $250 and replaced the board (and wax motor to be safe ) and everything was peachy for exactly 3 loads and 32 hours; in the middle of the 4th load it just died. Opened it up again and the same failure, the 3 most expensive loads of laundry in my life.  Anyway have you heard of this?  Something is shorting out the 24V supply, but not immediately it took a few loads.  My guess is that something is drawing a lot of current on the 24V until the transformer shorts and 120V starts flowing through the pins which ultimately create enough current to fuse the trace.  If this is the case it may not necessarily be the motor board thatís causing the short.

Any experience with this? This might be the last straw for this machine.  Any help would be greatly appreciated.

Model MAH4000AWW

Offline Repair-man

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Re: Fused 24V trace on Machine Control Board
« Reply #1 on: May 06, 2009, 10:57:27 AM »
The best and most likely spot for the 2 voltages to mix are in the timer, but your problem sounds more like a short. Have a look at your wiring diagram in the console and note which sections are high and which are low voltage. Also, the wax motor runs on 120 volts, so it is not the culprit here.

One of the 24 volt components may be shorting out. Check the off-balance loop that runs around the tub, paying close attention to the bottom limit switch there on the front of the tub flange.. This loop is a 24-volt circuit. There are 3 switches in series here to OHM out at the harness connector uner the main top.

Also, the tachometer circuit on the motor is also 24 volts. Could need a new motor & board kit. The P-4 connectors control this input.
« Last Edit: May 06, 2009, 11:04:34 AM by Repair-man »
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Offline dpecorella

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Re: Fused 24V trace on Machine Control Board
« Reply #2 on: May 06, 2009, 12:01:19 PM »
Thanks for the reply. Now that the trace is fused,  I did ohm out the 24V pin on the P4 CONN to the return (white wire) and it read 160 ohms, which doesn't seem right.  I did the same for the 24V pin on  the CONN P3 and it was ~24k ohms, which seems more reasonable.

If I have to replace motor, the motor control board, and buy another new machine control board, it looks like this is going to be expensive even if I do this myself.  Might be worth it to just get a new machine.

Offline Repair-man

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Re: Fused 24V trace on Machine Control Board
« Reply #3 on: May 06, 2009, 03:54:02 PM »
Unless you are emotionally attached to this machine for some reason, it would not be considered impractical to go ahead and invest in a newer model. Especially since you will eventually reach the stopping point when the tub bearings go out.

When my Neptune Mah5500 finally goes out, I am purchasing the Whirlpool Duet, only because it is cheap and easy to get parts for down the road, and that's what you have to focus on these days . word up
"It's only expensive if someone else fixes it for you" -
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Offline dpecorella

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Re: Fused 24V trace on Machine Control Board
« Reply #4 on: May 06, 2009, 09:14:47 PM »
Thats what I'm gonna do.  For the same money I could get a new machine and a manufacturers warranty.  No attachement issues here, in fact I harbor contempt for the thing.  The last time it failed I was out of town and my wife told me there was water leaking from one of the recessed lights in the kitchen. 

The problem was the effect of vibration on recirculation hose.  The retention clip gave way and the hose was rubbing on the counterweight which, as you know, is basically a cinder block!  Wore a hole right through it.  The vibration was enough to also wear a hole in my drip pan.  Rainforest ensued.

This thing is possessed.   I think a new machine and an exorcism is in order.

 

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