Our Kenmore Elite 30″ Induction/True Convection range recently developed a problem where the oven would not come to temperature in the expected time, nor would it ever attain the expected temperature.  The Model number of the unit is 223 666 003 with a manufacturer number of 970-66003. However this repair applies to any number of similar ranges from Frigidaire,  and others.  A web search will turn up cross references on many of the parts suppliers.

This range was purchased in 2008, therefore certain specific parts are no longer available from either the manufacturer or typical online suppliers. There is a healthy secondary repair market which successfully does board swap/repairs, as well as numerous common parts which have been widely used over the intervening years. Again, these are easily found by a simple web search.

The part in question was the combination controller/relay board, which appeared to be designed by Electrolux, and made in China by various manufacturers. The part number was Electrolux 316577079.

I could hear the relays clicking as the display indicated the various heat sources: Lower element, upper element, convection fan. All the functions of the oven worked as far the control panel and interface showed. This suggested that the controller was fine, but the relay board had a problem.

A bit of research suggested that some of the solder joints on the relay pcb were subject to cracking. This oven was manufactured soon after the introduction of the RoHS Directive (Restriction of Hazardous Substances), and uses lead free solder on the circuit boards. Lead free solders have been shown to be more brittle and subject to cracking under certain conditions than lead based solders. An excellent article comparing the properties of lead free and lead based solder can be found here.

I removed the boards from the oven and visually inspected the solder joints on both of the boards under magnification. I found cracked solder joints on the relay board in the indicated areas:

I suspect that the solder joints on this relay board were unsound from the start and prone to crack initiation over time. Crack progression lead eventually to a gap forming around the joint. This resulted in current arcing across the joint and causing erosion and vaporization of the solder. Ultimately, this resulted in the the arc damage visible at the pcb through hole and the resulting problems with the oven heating. That particular relay is a 10 A 240 V AC relay for the heating elements.

I also found cracked solder joints at several of the pins on the connector indicated on the relay board.

In my opinion, some of these problems were attributable to the early days of RoHS implementation, and the lack of understanding and experience in the use of lead free solders. My experience suggests that industry has advanced some way in both the formulation (alloy content and chemistry) and soldering techniques using lead free alloys.

I replaced the large AC relay (which had arced across the pin), and removed most of the solder from any suspect joints with solder wick. I then re-soldered the joints with Sn62Pb36Ag2 (tin, lead, silver) solder that I use for my vintage electronics work.

After re-installing the boards and display, I found that the oven functioned correctly and came to temperature as expected.