How I Spent My Weekend 2

Thread Starter

panic mode

Joined Oct 10, 2011
2,715
Ha...!

Sounds a lot like my weekend. I spent few hours yesterday working in our kitchen...

Of course i did not need stars to align, it was enough to hear my star (wife) complain that for the past few days dishwasher did not work and also range just failed the day before. I bought and installed those few years ago and was just pondering to investigate or just get new ones... But that would be wasteful and would not quiet my wife - she loves new things but keeps on ranting how new appliances are delicate while in the old days they were meant to last and be repaired. So i had to get on my knees and use tools. Dishwasher was actually ok, no leaks (ok i created a small spill but quickly fixed it, i don't do this every day...) , everything was neat and tidy, even door seal did not look too bad for something that is used so much. But as i took its guts out, there were some solids impeding water flow so sprayers did not receive enough water. They looked like vine glass remains (three thin shards) and two olive pits, toothpick and small piece of plastic wrap. The only annoying thing is that i am not as limber as i used to be and the damn door was in a way - not something to lean on when putting back sprayer arm. But mission accomplished, wife was quiet and i got my cold beer.

Next mission was range - also Kenmore. And electric range is just a big resistor - how complicated can it be? My angel (when angry, turns to harpy) kept on insisting that bottom heater element must be replaced since her baked goods only got crisp on the top. Which was a good tip but i was not going to just replace something without checking it out first. That's what multimeter is for and i happen to have bunch of them. Another pleasant surprise was that the back side of the appliance had pocket with crude schematic. It showed all connections and wire colors (but no details for control board).

Unplugged power checked heating elements and they were all ok - including bottom one labeled "bake". Wires went straight to controller with pair of white relays and few black ones. Two white relays were used to control broil and bake elements. Checked online, they cost some $3-4 which is nice but i still needed another look. I am used to troubleshooting of servo drives and working on live circuits with 600VAC and 800+ VDC. This little 240V range feels like a toy - everything is so ... simple.

I power it up, start bake, relays click, no power on bake element. Switch to broil and there is power on broil element. power down swap wires on heater elements and try again (just in case element may still have an intermittent problem, something that may not be observable with continuity check). Turns out both heater elements are definitely fine. Issue must be on the control board.

Controller was SF5322, it is actually two PCBs, connected on side by bunch of jumpers. Took some praying to get the boards out. One is the front or HMI with 7-segment display, LEDs and buttons and was fitted with a larger chip labeled "spitfire" (obviously an MCU). Other PCB was PSU and driver board containing relays and ULN2803. Both PCBs are just single layer construction with through hole components so literally anyone can work on it.

Everything looked fine and neat, measurements were reasonable (270 Ohm for coils, zero Ohm for NC, open for NO contacts). Two inverting contacts were paralleled on both relays.There was another larger relay that was switching power of another phase but this was common to both broil and bake elements and not an issue. Problem was on pair of white relays. Looking closer i see that power to bake elements goes through both of them, first it goes through NC of the broil relay then through NO of bake relays. So broil relay contacts are used all the time to power either broil element or bake element. I suspected that working contact of broil relay may be failing, after all it is the component working hardest. So I decided to label relays, de-solder them and if they still looked good, put them back but - swap them. Solder sucker and 35W soldering iron did job in seconds. Mission #2 accomplished - range works. I am planing on ordering pair of replacement replays with my next parts order but this is good for now. Let the baking continue...

Replacement controller was some $120USD + shipping.
Nearby place that sells repaired controller ("timer") wants some $170CAD for it.
https://www.appliancetimers.ca/detail/Range/brand-Kenmore/model-SF5322/7435

Simply swapping places for two relays gave the controller new life. Pair of new replays will be bargain (OZ-SS-112LF):
http://canada.newark.com/te-connectivity/oz-ss-112lf-000/oz-ss-112lf-000/dp/90R8163



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