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LG LDF6920ST dishwasher heater turns on when door is closed


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16 replies to this topic

#1 TimBeckler

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Posted 20 May 2013 - 01:15 PM

Hi, My LG LDF6920ST dishwasher just started an interesting behavior.

 

I opened it the next day after it finished it's wash cycle and the thing was very warm and full of steam!

I then discovered that even with the power button off, the heating element is getting hot when the door is simply closed.

If you open the door you can hear a sizzling sound that gradually stops when you open the door. Close the door for 10 seconds and open it again you can hear the sizzling sound again.

 

I have taken the door apart and reseated all connectors but it did not help.

 

Any ideas as to what part failure might cause that? I'd appreciate any input.

 

Thanks!

 

Tim

 

 



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#2 Samurai Appliance Repair Man

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Posted 20 May 2013 - 01:26 PM

Most likely a stuck heater switch in the door latch assembly:  http://www.repaircli...umber=LDF6920ST

 

 

Door-Latch-4027ED3002A-00719102.jpg

 

Can use your ohm meter to see if the NO and NC contacts switch when the latch is actuated.  Here's your wiring diagram:

 

gallery_4_7_207890.jpg

 

 

Check the thermistor resistance and replace if out of spec:  http://www.repaircli...umber=LDF6920ST

 

 

Sensor-6501ED2002H-01372305.jpg

 

 

 

 

If both of those check good, then the main control board is keeping voltage on the element and it should be replaced:  http://www.repaircli...umber=LDF6920ST

 

 

Main-Control-Board-6871DD1006Q-00727530.



#3 TimBeckler

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Posted 20 May 2013 - 05:35 PM

Thanks much! Unfortunately, it's looking like the PCB is bad. Appreciate your help. Thanks again



#4 Samurai Appliance Repair Man

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Posted 20 May 2013 - 05:37 PM

Please let us know how it turns out!

#5 TimBeckler

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Posted 02 June 2013 - 08:10 PM

Well, I'm afraid a new PCB did not help. The micro-switches in the door open and close normally per my ohm meter and the thermistor is at 14K ohms when I measure across pins 4 and 5 of the unplugged RD6 connector. That seems to be in range. Dang, any other things I should check?



#6 RegUS_PatOff

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Posted 02 June 2013 - 08:44 PM

The Heater may have a partial short to it's case / ground.

Disconnect the Heater and OHM check for a short to it's case / (damaged?) sheath.

 

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#7 PDuff

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Posted 03 June 2013 - 01:26 PM

Also check heater wire harness for short to ground (chassis).  Check wire harness for damage at bottom/right corner of door liner.  Be sure main power connections in box located behind bottom access panel haven't shorted.



#8 TimBeckler

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Posted 03 June 2013 - 07:53 PM

Thanks for all the feedback.

 

OK, I've unplugged RD3 and BL4.

 

RD3 just has two wires, one to the heater, the other to the far side of the door switch

 

Resistance across pins 1 and 3 of RD3 is infinite with the door latch open, as I would expect

 

Goes to 4-6 Megohms (kinda jumps around) with the door latch closed.

That is the same resistance from RD3 -pin3 to ground, and from RD3-pin 3 to BL4-pin 1

 

The diagram shows that heater resistance should be 11.8 ohms but I'm not so sure that's correct  (unless I'm missing something...)

 

The wiring harness is well protected in a heavy plastic sleeve where it goes underneath. I can't see anything wrong there.

 

Beside this odd problem, the dishwasher works fine otherwise. :kopkrab:



#9 RegUS_PatOff

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Posted 03 June 2013 - 08:07 PM

The Heater may have a partial short to it's case / ground.

Disconnect the Heater and OHM check for a short to it's case / (damaged?) sheath.


.

one of my video productions: “Easter Seals: Walk With Me”

every day is Down Syndrome Awareness Day
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RegUS_PatOff > www.youtube.com/watch?v=oPAY2LsKVEw

#10 TimBeckler

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Posted 03 June 2013 - 09:39 PM

OK, I disconnected all plugs from the pcb and measured from RD3-pin 3 to the outside of the heater sheath.

 

Got about 2 Megohms so I don't think it's shorted.



#11 RegUS_PatOff

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Posted 04 June 2013 - 03:04 AM

OK

It's either a bad Controller, or a short in the wiring.

With everything connected, but power removed from the DishWasher Power Cord,

(and Door closed)

measure from each of the connections on the Heater to:

chassis / ground

Neutral

Line


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#12 TimBeckler

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Posted 04 June 2013 - 02:48 PM

Thank you.

 

RD3-pin3 to:

Gnd:3.3 Megohm

Line: 120k ohm

Neutral: 6 Megohm

 

Other side of heater at the switch connector in the latch:

 

Gnd: 300k ohm

Neutral: 3 Megohm

Line: appears to be direct short,

 

RD3- pin1 is shorted to line on the pcb (with RD3 unplugged)

 

if I unplug connector WH3, the short at RD3-P1 goes away

With WH3 unplugged, the white wire at pin 1 is shorted to line.



#13 RegUS_PatOff

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Posted 04 June 2013 - 03:56 PM

Line: appears to be direct short,

 

RD3- pin1 is shorted to line on the pcb (with RD3 unplugged)

 

if I unplug connector WH3, the short at RD3-P1 goes away

With WH3 unplugged, the white wire at pin 1 is shorted to line.

that may be normal, but in order for the Heater to be ON when the Door is closed,

RD3-3 would need to be at Neutral somehow...

would seem to be a bad Controller ?


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one of my video productions: “Easter Seals: Walk With Me”

every day is Down Syndrome Awareness Day
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RegUS_PatOff > www.youtube.com/watch?v=oPAY2LsKVEw

#14 TimBeckler

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Posted 04 June 2013 - 10:26 PM

It sure seems unlikely that an old a new controller would have the exact same failure.

 

What if the float switch thinks the tub is full of water, when it's not? How would I test that?



#15 RegUS_PatOff

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Posted 04 June 2013 - 11:04 PM

shouldn't heat the water if the Power Switch is OFF


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one of my video productions: “Easter Seals: Walk With Me”

every day is Down Syndrome Awareness Day
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RegUS_PatOff > www.youtube.com/watch?v=oPAY2LsKVEw

#16 TimBeckler

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Posted 15 June 2013 - 07:20 PM

Well, finally got it fixed. The heating element had burned completely through.

 

Thanks for all the help. Anyone need a new 6871DD1006Q Controller? Only $50!

 

#17 Samurai Appliance Repair Man

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Posted 16 June 2013 - 07:16 AM

Good job! Thanks for posting whatcha found!




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