clothes dryer control board has burnt trace

[Agentfoot]

Its a Whirlpool electric clothes dryer. Found the trace for the power side of the motor control relay smoked. Relay was still functional but had burnt contacts. My first thought was a bad motor or start/run caps for the motor. But then I noticed the circuit has a thermal fuse. If there is a issue with the motor or caps shouldn't the thermal fuse go before a trace? Unfortunately I only have the control board right now so I am unable to test the motor or caps. I would like to know what could have went wrong here? Still learning this electronics stuff.

[Ian.M]

That's what happens when a dry joint cracks round the pin, and starts arcing across the crack.  You'll need to dremel out *all* the charred PCB material,  glue the new relay in place, solder its other pins to the undamaged pads, and fit a wire link between the pin in the middle of the hole left by removing the damaged area, and the undamaged part of the burnt track.   While you are in there, resolder all the other relay contact pins, and any other pins on wide tracks with joints that look even a little bit suspect!

[Agentfoot]

Thanks for the reply. A Cracked solder joint did cross my mind but I figured that was a long shot due to the damage. Guess i have to take in account the voltage and amperage going through there. Does burnt pcb become conductive? Is that why you say to remove all the burnt pcb? Is the glue to prevent vibrations that may cause future cracks?

[Ian.M]

Yes, yes and yes!

To elaborate: Carbonised PCB is conductive.  Partially carbonised PCB will be resistive.  Therefore the damage has degraded the creepage and clearance distances (between neighbouring conductors) required for safety and normal operation, so all the char must be removed, back to sound PCB material.  This will leave that pin of the relay unanchored, so it must be either glued down to prevent excessive strain on the other pins, or the PCB itself must be repaired, which is far from simple if you haven't done it before.

[IanB]

I have repaired a similar fault (twice) on my Bosch dishwasher. The first time time was when there was a smell of burning in my kitchen and I couldn't tell where it was coming from, until I noticed that my dishwasher was running way past the time the cycle was supposed to finish without reaching temperature. I opened it up and found the burned track and joint, though not quite as dramatic as yours. The second time was when my repair wasn't good enough, and it happened again.

In the case of my dishwasher it was the heater current that was going through the PCB track, not simply motor current.

I honestly think it is a very dubious design to run mains power on a PCB like that. In the old days there would have been proper wires, crimp terminals and spade lugs to carry the power. Due to the mains voltage behind it, any slight weakness like a cracked or dry solder joint is not going to stop conduction, it is just going to become a (very) hot spot until destruction occurs.

When I did my repair the second time I reinforced the trace with some additional copper wire and plenty of solder.

[floobydust]

Fractured solder joints on relays did cause Whirlpool dishwasher fires, with subsequent recalls over that after house fires.
OP I would contact Whirlpool about the smoke, and check if that model has a related recall, see what they will do.
Otherwise toss the board in the garbage instead of repairing it, as the carbon on the board likely has mains power on it all the time and not what I'd want in my home.
Note the PCB trace fuses Whirlpool also incorporates on the boards.

edit: I also believe the high vibration in a clothes dryer is hard on the circuit boards. The white enclosure being UL 94 flameproof plastic did not work for the dishwashers.

[Kim Christensen]

I would like to know what could have went wrong here? Still learning this electronics stuff.

High current relays on PCBs are known for cracks around their solder joints. The constant thermal stress (heating/cooling cycle) as the relays turn on/off causes the joints to crack. When the relay contact gets pitted like yours is, this adds more resistance to the contact, which creates more heat, and so the problem manifests even quicker.

[Agentfoot]

Thank you all! Your experience and knowledge is priceless to me.

I'll reach out to the manufacturer to see if they will do anything. If not I will repair it and post my results.

It is a shame things are engineered to fail these days. I noticed the "fusible trace" that sends mains power to the transformer. Looks like most of the small components were covered in epoxy to protect them from vibration and maybe moisture. But none of the large components have any sort of vibration protection. To make things worse most of the large components are dealing with mains voltage.