Clothes Dryer Repair Help - Burned PCB pics...

[alank2]

The wife tried to start up the dryer today and said she saw a spark and had some smell.  I went in and tried to start it and a huge spark that came from a relay area was visible through the control panel.  Bad smell.  God it unplugged and taken apart and cleaned off most of the giant black soot all over it.

It looks like there is a trace going into a relay completely burned and rolled up a bit (see picture below).  Not sure if the front side of the trace is still intact.  This is 240V so there is a L1 and L2 with 240V between them, and a neutral in the middle.  The side that burned is labeled 9 but you can see this on the pcb any longer.  It is a piggy back cable from L1, see sch.  The other side of the relay (10) looks fine and goes to the heater coil.  I measured between 10 and 16 and get 39.5 ohms across the heater coil.

The relay (both of them) seem to work fine.  Open with no load, and 9v across the coil closes them.  Even the one with the burnt trace...

For this surge of current, must 10 have been shorted to ground or neutral in some way?  I see no damage to it.

I can possibly repair the PCB and solder the 9 directly to the relay to bypass the burned trace, but I'm still trying to figure out what went wrong here first.

Any ideas? 

[ddavidebor]

Look at the various video on "paceworldwide" youtube channel
You'll find a series of video on repair, and one on repair of pcb.

[NiHaoMike]

Check for an intermittent short in the heater. Then bypass the burned trace with a piece of heavy wire.

[bilko]

Check for an intermittent short in the heater. Then bypass the burned trace with a piece of heavy wire.

It looks like your relay contacts are fried. I would do as Mike suggests and replace the relays. Contacts are high resistance, that's where the heat is coming from.

[IanB]

My Bosch dishwasher failed in a similar way. The design is trying to feed a high power mains circuit through solder joints and PCB traces. This is an inherently unreliable arrangement. It will seem to work fine as long as the assembly and integrity of the circuit is good, but as soon as you get a hint of a high resistance solder joint or a cracked PCB trace the thing will go up like a firework.

You have a system with a puny, feeble little PCB circuit in series with a big high power load and a high voltage, low impedance supply. The mains voltage in this situation is a force that will not be stopped. A tiny crack in the solder joint will cause arcing and high temperatures. Any small amount of charring around the arc and in the circuit will act as a resistance heater that will glow white hot as the mains current is forced through it.

What I suggest you do is clean the burned and charred area as thoroughly as you can, and then remake the connection to the relay with thick copper wire and very solid joints.

IMHO the design is bad and would never have been seen in the old days of reliable consumer products.  The relay should be fitted with spade terminals and the mains wiring should be directly attached to the relay terminals with crimped spade connectors. There should be no solder joints or PCB traces in the current path. The bad design is an outcome of cost cutting and automated assembly. It requires more manual steps in the assembly process to do the design properly.

[alank2]

So I have two theories at this point, both of which make sense, but how can I figure out which one is the right one.

#1 - There is an intermittent short in the heater coil that I don't see when measuring it cold, but when it warms or gets hot it must short through ground or neutral in some way to cause the over current situation.

#2 - The PCB was what caused the issue completely.  The joint/trace heated up from the normal amount of current and caused it to burn/fault.

Does #2 not imply an over current situation?  It sure seemed like one.

Let me add one more detail.  My wife saw both flashes.  She said the first one was much less bright.  The second one we both saw was much brighter and stronger.  Could the first one have weakened the pcb trace and the second one did it in?  Does this suggest or lend to #2 more than #1 above?

[bilko]

#2 - The PCB was what caused the issue completely.  The joint/trace heated up from the normal amount of current and caused it to burn/fault.

Does #2 not imply an over current situation?  It sure seemed like one.

Let me add one more detail.  My wife saw both flashes.  She said the first one was much less bright.  The second one we both saw was much brighter and stronger.  Could the first one have weakened the pcb trace and the second one did it in?  Does this suggest or lend to #2 more than #1 above?

See my previous reply, worn out contacts in the relay will generate enough heat to MELT the solder joints. The bad joint is likely to be a symptom, not the cause. I haven't looked properly but I don't see any contact suppressors either, poor design, disposable product.

[david77]

This is a very common problem with high power house hold devices. As mentioned above most of the time the cause is slightly elevated contact resistance in relays or on spade terminals. They heat up until something burns or melts.
However, this does not explain the violently burnt out trace on your board. I'd suggest checking the heating element more closely.
Make a resistance measurement from 10 to the purple wire and compare that to the reading you get from 16 to the purple wire. I'm talking about the purple wire that goes from both heaters to the switch on the right side of your diagram.
If the values deviate significantly you've got your faulty heater.

[Psi]

Heater shorts in clothes dryers are usually caused by the metal wire inside a bra coming out and getting caught up in the heater elements behind the back panel.

[bilko]

However, this does not explain the violently burnt out trace on your board. I'd suggest checking the heating element more closely.
Make a resistance measurement from 10 to the purple wire and compare that to the reading you get from 16 to the purple wire. I'm talking about the purple wire that goes from both heaters to the switch on the right side of your diagram.
If the values deviate significantly you've got your faulty heater.

The heater power may not be identical for both heaters
Check the resistance of the individual heaters and work out the amps and power.

[IanB]

See my previous reply, worn out contacts in the relay will generate enough heat to MELT the solder joints. The bad joint is likely to be a symptom, not the cause. I haven't looked properly but I don't see any contact suppressors either, poor design, disposable product.

I understand a relay fault is a possibility, but I consider it a lower probability than a failed solder joint on the board. Note how the spade terminals 9, 10, J and 16 are soldered in to the PCB, and are subject to mechanical stress when the spade connector is attached to them with the wires dangling off. The relay itself is designed for high voltage, high current duty with inductive loads (note the HP rating). It probably was still within its expected operating lifetime.

So called "dry joints" have always been a problem, especially with lead free solder processes. At low voltages a cracked joint just produces an intermittent failure. At mains voltages a cracked joint produces a damaging high power arc. Consider that if you used the heater as ballast you could do arc welding with the mains (see videos from other parts of the world where people actually do this).

In the picture, examine the area around the base of the spade connector. Notice that heat lines radiate outward from it, and notice that on the underside the copper trace has de-laminated and peeled away from it. All of this points to the spade terminal solder joint as being the initial point of failure.

What I suspect has happened is that the solder joint cracked, causing a high resistance point in the circuit. The mains current arced across the gap, melted the solder and further weakened the current path. A large arc developed, fed by vaporizing material from the heat, and spread down the copper trace towards the relay. Eventually the resistance became high enough that the circuit was interrupted and a mess was left behind.

Edit: s/become/became/

[bilko]

What I suspect has happened is that the solder joint cracked, causing a high resistance point in the circuit. The mains current arced across the gap, melted the solder and further weakened the current path. A large arc developed, fed by vaporizing material from the heat, and spread down the copper trace towards the relay. Eventually the resistance become high enough that the circuit was interrupted and a mess was left behind.

Ok, after taking a closer look, it is likely that the spade terminal made a loose connection, the heat developed melted the solder at the base of the connection. Notice also that the track that is connected to the relay is completely vaporised. I suspect that the track was glowing hot and that melted the relay / PCB joint which was the cause of the white flash

[alank2]

Thanks for all the help and advice everyone.  I've pulled the relay and to me it looks like perhaps there is NO TRACE on the topside of the pcb.  The surface has the same pattern that other plain areas of the pcb does - do you guys agree that there may not have been a trace here?  The other relay looks like it has one...  Could this be a defect or bug or do you guys think the trace was vaporized away?  BTW, the trace on the backside was rolled up...

I'm thinking of replacing the bad relay with another and just mounting the high voltage wires directly to the relay.  Do you think I need to add any additional fusing to make it like the original design where the weak crummy pcb trace in this case acted as a fuse?

[duskglow]

It does not look like there was supposed to be a trace on the top side of the board.  If you think about it, the traces being on the opposite side of the board helps with isolation.

[alank2]

It does not look like there was supposed to be a trace on the top side of the board.  If you think about it, the traces being on the opposite side of the board helps with isolation.

Except that the other relay right next to it has traces on both the top side and bottom side of the board.  It also has a trace on the top and bottom of "10".  So, 3 of the 4 connectors have traces on both sides of the board except the one that only had one side, which was the one that burned...

[david77]

Smells more and more of excessive current flow to me...

[alank2]

Smells more and more of excessive current flow to me...

Meaning heater coil fault?

Is there a way to test this other than to put current through the heater coil and see what happens?  To get to the coil I have to take it all apart, remove the drum, etc., and I'd rather not unless I have no choice.  The heater coil is a $100 part from what I've seen and given its age I'll probably just go get another dryer.

My current plan is to get an appropriate replacement relay with spade terminals on it and see what happens...

[duskglow]

Hmm, good point, but there's still no obvious evidence of another trace.  That would show as burned on the top of the board like the bottom one.

[alank2]

Hmm, good point, but there's still no obvious evidence of another trace.  That would show as burned on the top of the board like the bottom one.

I completely agree, could it have been a bad pcb or a missed trace?

[duskglow]

I wouldn't think so.  I think you're looking at a fault, not a design failure (beyond the fact that this high current is on a PCB in the first place).

[alank2]

A fault beyond the PCB?  To me this sure looks like a high current situation, but I've never seen what a poor week connection looks like getting super hot and burning up so would that look the same or different than this???  If the heater core is toast I'm not sure I'll waste time trying to repair the relay...

[nukie]

When you are done can you please dissect the crappy relay to reveal the relay contacts? Some relay contacts oxidise over time the resistance increases.

Sent from my Nexus 10 using Tapatalk 2

[Paul Price]

If there were a fault in the heater it would damage the wiring to both contacts of the relay..it did not. The other contact is in pristine condition. You might have had a bad relay contact, but I doubt it. You probably had only one relay connection cold solder joint develop after many moons and this bad connection heated up and developed into an arc that ate it PCB trace towards the press-on connector at the edge of the board. The photo show the spade connector having a good solder joint, it is not charred at the spade terminal itself. If you had a shorted heater element both wires to the relay would have vaporized from the same short circuit. Remember the electronic basics, this is a series circuit and the current is the same on both sides of the relays contacts...yet one side is unharmed. The rely is probably good. You can check its contacts with a 12 volt supply or even a 9V battery and use an ohm meter. If you notice anything more resistance  than a direct short when the relay is activated, then the relay needs replacing, otherwise it is probably ok. I would just solder a wire to the relay contact that is burnt and connect it with a crimp connector male-female spade connection to the original wire, scrape off the carbon and  you are done with it. The is no indication that there was any trace on the other side of the board.

[duskglow]

EDIT:  removing this comment.  I thought for some reason it was the actuator part of the relay.  I REALLY need to get more sleep.

[alank2]

The relay did still work when I put a DC voltage across the coil.

I just cut the top off the relay - what am I looking for?  I can see the high voltage contact and it looks white-ish with a pattern or possibly pitting in it.  I haven't disassembed it further yet to get a good look, I'm only getting a narrow look from the top...