Hot Capacitor!! buzzing in relay Dishwasher help.

Thread Starter

fixing stuff dad

Joined Aug 17, 2023
6
I have a older whirlpool dw that started making a buzzing noise intermittently during the wash cycle. I felt a hot area on the control panel opposite the side of the heater that still remained hot after several days of no use. I opened up the control panel and found that the 2 larger electrolytic capacitors were very hot. (maybe its just one but they sit close enough to heat the other). I ran the DW with the panel open and heard distinct buzzing from the relays but couldnt isolate which one. I unplugged the power to let the capacitors cool, ran it later, and it was a much quieter buzz. So, Im guessing a cap has gone bad? and is effecting the relay? and figure replacing the cap(S) will resolve the problem? Just looking for more thought from smarter people.

Handy but no expert, dabble in circuits at basic level.
 

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MaxHeadRoom

Joined Jul 18, 2013
28,768
Normally relays do not buzz on full wave rectified AC , even without capacitors.
But certainly sounds like you need to replace the caps, also check the DC in the event a diode rectifier has opened?
The area close to R32 - D16 looks as it has sustained some heat?
 

Thread Starter

fixing stuff dad

Joined Aug 17, 2023
6
Normally relays do not buzz on full wave rectified AC , even without capacitors.
But certainly sounds like you need to replace the caps, also check the DC in the event a diode rectifier has opened?
The area close to R32 - D16 looks as it has sustained some heat?
Thanks so much for replying!! I noticed the that area too that looked like it got hot. When i was looking at replacement board $100, I noticed that some seem to have the same discoloration, so may be from initial build?

(I couldnt find a schematic,) not that id be able to fully understand it. To show my newbness. I understand what relays, diodes, transistors, rectifying is but i look at a board like this and am lost out how it all comes together. I cant see how things come in to the caps or where they lead and how the AC is actually rectified to DC. I assume the d6 and d7 lead to each cap and this is there to smooth some voltage to wherever it is going, to the relays? Im tying to learn this stuff better. Can you suggest where i should "check if the diode rectifier id open"? But at very least i can very easily replace the caps.
Thanks
 

MaxHeadRoom

Joined Jul 18, 2013
28,768
It would need some initial reverse-engineering of the power input and determine where the DC supply is fed from and go from there with a few voltage tests etc.
 

Dodgydave

Joined Jun 22, 2012
11,318
Looks like a transformerless supply with the Orange capacitor and the two diodes D6/7 , can you take pictures of the track side , and what voltages are across the capacitors?
 

Thread Starter

fixing stuff dad

Joined Aug 17, 2023
6
Looks like a transformerless supply with the Orange capacitor and the two diodes D6/7 , can you take pictures of the track side , and what voltages are across the capacitors?
Thanks for replying. Here is the back of the pcb. Yeah i saw that big red cap and was thinking it had some role in the AC to DC. To be honest i know how to do some testing on caps with a VOM when they are not installed. Im not sure how to test the voltage across the caps on the board?
 

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Dodgydave

Joined Jun 22, 2012
11,318
Just a quick diagram, looks like the capacitors are producing the +/- 6V supplies with the Zener diode D32. C13 is the Orange capacitor feeding AC into the diodes D6& D7, check the voltages across the capacitors when powered up to see what is going on and across the Zener diode D32.IMG_20230821_104306.jpg
 

Thread Starter

fixing stuff dad

Joined Aug 17, 2023
6
Just a quick diagram, looks like the capacitors are producing the +/- 6V supplies with the Zener diode D32. C13 is the Orange capacitor feeding AC into the diodes D6& D7, check the voltages across the capacitors when powered up to see what is going on and across the Zener diode D32.View attachment 300943
Thanks for your patience and help.
To be 100% clear, attached and under power of the DW touch the small caps directly across each pin with the vom leads to get a voltage reading. And the diode. (I understand it should be low dc voltage. Just wanna be safe and not fry the whole board too.)
 

Dodgydave

Joined Jun 22, 2012
11,318
Yes put the voltmeter across the capacitors on DC, it will have a value on it , ideally the capacitors have a value on their side so it should be lower than that value. As for the zener diodes the same on DC , you should be reading 6V approx.
 

Thread Starter

fixing stuff dad

Joined Aug 17, 2023
6
Here is the same pic but i added in the voltage. I checked a couple of times. My interpretation is a higher voltage comes from the big red cap and the diodes d6 27v and d7 13v (because it is reversed) feeds 40v in to the 2 caps that are rated 63V each. I cant tell how it flows from there or where it goes next but the 2 smaller caps rated 10v are getting around 5v each. Of note is that resistor R32 is very hot and 12V? with diode d16 is 20v? but not sure whats going on in that area anyway?? (I have stared at it a lot to try and understand the flow and what it should be)
Thanks
 

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Thread Starter

fixing stuff dad

Joined Aug 17, 2023
6
Yes put the voltmeter across the capacitors on DC, it will have a value on it , ideally the capacitors have a value on their side so it should be lower than that value. As for the zener diodes the same on DC , you should be reading 6V approx.

What do you think of the voltages i got ? esp. around R32 and d16? I ran a load in the DW and the buzzing isnt as loud but there is still a fainter zzzzzzzzzzzzz noise, im guessing in the relay still
 

Dodgydave

Joined Jun 22, 2012
11,318
I don't understand why the resistor R32 has 12V on one end and 20V on the other, ? What is this relay feeding to cause the buzzing.
 
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