AEG T57840 Tumble Dryer motor problem with faulty circuit board

Hello Paul, I got the dryer fixed! The motor wires on the card edge connector were a small part of the problem since they did not like it when I disconnected the connector several times during troubleshooting. I finally soldered them to the connector and got rid of that problem.The dryer motor, however was still acting up. I took the PCB out again since I had narrowed the fault down to a very small area in it. It seemed like the Triac was not connecting as it should. The relay was new and nothing wrong in the PCB traces either on the output side. So it must be the triac or the gate drive...I measured the triac gate drive circuit all the way back to the microcontroller and found that it had a buffer driver which was obviously working OK. Between the buffer and the Triac gate were just a 47 ohm resistor R99 which is located right next to the only mounting screw of the PCB! Bingo - bending the PCB a bit makes the resistance value jump from the 47 ohm up to 1 kohm. This is a design flaw since a SMD resistor should not be located that close to a mounting screw, especially in an appliance that may vibrate. If you take a look at the attached image, you'll see the resistor in the middle. Here I have already replaced the original 1206 47 Ohm SMD resistor with a 47 Ohm Minimelf resistor (since I did not have a conventional SMD resistor at hand). The Minimelf resistor might actually be more tolerant against the abuse so it is good. To eliminate at least part of the vibrations and bending of the PCB, I added an O-ring under the screw when I mounted the PCB back. Now the machine runs like new again, does not hesitate at all. You are welcome to spread this information to others and I hope you do it since this seems to be a common problem with this particular PCB version and is very easy and cheap to fix.   Cheers,     

Risto