Help for an electrical feebe.....
 

Jenn-air gas stove/oven.

Digital display for clock and oven controls work intermittently. If I tap the yellow thingie in the circuit board pic it buzzes lightly, display/oven controls work but shut down after ten minutes. If I get it started and tap it again (butt of screwdriver - just a wee tap) it will stop buzzing and the display stops.

Calls to the appliance parts guy in town indicate the board needs replaced and that trying to fix the boards is a challenge even for pros and they just replace board in-kind.

That said, do I have a remote chance of fixing this or should I just hang it up and get another board? I am assuming that tapping the yellow thingie may be simply transferring the impact "shock" to the rest of the board, and the intermittent failure point is simply jostled causing it to work for a few minutes until heat breaks a connection.

However, if the yellow thingie is not supposed to buzz, perhaps that individual part could be scrounged up and replaced?

Just a wild shot asking here but I have gotten better input here on odd-ball topics that I get on specific topic boards.

Edit: I can wiggle connections and the yellow thing and nothing happens - only when i tap it does the display come back on.

Note heat damage on clock face - plastic cover has warped from heat leaking out of oven case into the circuit board area. Also, control circuit board is directly behind the clock.

http://forums.pelicanparts.com/uploa...1373056686.jpg

http://forums.pelicanparts.com/uploa...1373056726.jpg

The yellow thingie looks to me like a transformer used to change voltages. If the windings are shorted that could explain the buzzing. If you can pull a part number off it, it might be worth a shot. Looks like its connection is modular.

You need to use a meter and monitor the output of that transformer to determine if it is defective before buying parts. And you are right about other things that can be the cause. I'm an amateur at this, but I think I see capacitors there and they do go bad.

yes- yellow item is a transformer. I'd suggest removing the power source and removing the board from the mounting location. Look on the underside at the solder connections over the entire board. It might be there is a joint with a small crack - and the tap vibrates the board enough to make connection. If you find anything suspect, use a solder iron to re-flow the solder at those junctions - re-install board and give it a try.

+1 on checking/re-flowing solder joints. Large, heat producing devices (e.g., the yellow transformer) are the usual suspects. I'd also check the solder joints on the large blue resistor in the middle of the board.

How is the oven heat getting to the board in the first place?
Is there a bad seal?
Should there be a thermal blanket over the board?
Drill hidden vent holes?

Good question on how is the heat getting there. I back-tracked on my google searches and found that Jenn-Air makes ovens with digital controls on the front top of the oven box - right above the oven vent - and these are the ones that suffer the heat damage. I found what looks to be heat marks on mine but now believe it was a boil over mess that came from the rear stove top burner as I see where liquid was dripping - this is all back inside the panel where the board is.

Good info. The front control panel stayed on for 20 hours this last time. I moved the blue resistor up just now as it was bent down a bit and the panel stopped working. No tap with screwdriver. Tapped yellow thingie and it started working again but only for ten minutes.

I think there is a chance this can be brought back to life.. Going to take board off and check joints.

Will advise on progress. Thanks much.

Symptoms definitely can be caused by cold or cracked solder joints. Difficult to see, but can interrupt signal. I would check and re-solder any joints that look suspect. You can even wholesale reheat each connection (time consuming) to refresh the continuity. You should be confident in your soldering skills before doing this, and it requires no new solder, just re-heating the joint until the solder turns liquid and re-hardens. I would confirm the integrity and continuity of all wiring first.

Pulled the board off as suggested. Look what I see at one of the legs of the transformer. Center of pic. If I flex the board a wee tiny bit the display comes on. Let off flex pressure - goes out. Cleaning soldering tool now.

Is rosin suggested even without new solder? This is a big fat pin so I am not worried about the actual task.

Thanks all. Things are looking up.

http://forums.pelicanparts.com/uploa...1373132190.jpg

Excellent. Flux should be good. Not much needed. It helps with the chemistry of melting the solder. Better to not introduce any new solder unless you have to. If so, it will have to be electrical grade.

I recently learned how to gas solder after a near disaster. Called two companies immediately but only one called back. Four days later:rolleyes:
The flux is crucial with new plumbing joints at least.
It bubbles and vaporizes at low heat, then vaccum pulls the solder deep into the joint.

Electronics are worth getting a good hot soldering pen. You don't want to heat the whole area.

It's all good. Job is done, working now and buttoning the stove up. I had to use a wee bit of solder and it "took" when I touched the pen tip to the board and pin at the same time. It takes no time to melt if you have the right stuff.

Last year I posted a pic of my soldering kit and got a helpful tune up.

http://forums.pelicanparts.com/porsche-911-technical-forum/677783-best-solder-electrical-connections.html

Had to drive quite a ways to buy the right stuff as home depot/lowe's/FLAPS don't have the right gear.

Thanks all very much.

http://forums.pelicanparts.com/uploa...1373135207.jpg

Fingers crossed but I think we nailed it :)

Awesome job! I love DIY that saves piles of cash. This world needs more self-sufficient people. It chaps my hide to just replace stuff that can be fixed.

Thanks.

Pretty gratifying when the parts place and internet both said full board replacement is the only option.

I have cooked a new variable speed furnace motor trying to do a DIY fix where the job was clearly over my head but this one was doable with the help here.

Bob, thanks for the link to your old thread. Apparently the consensus there would have you/me use no flux. Frankly, I don't think it's that bad as it should all come to the surface if the soldering is done correctly and you can clean it up after the joint is cool. I just figure there's going to be some oxidation on the existing old solder. Your board does look fairly new and clean.

I'll get the bill out to you on Monday - I'll apply the Pelican discount of course!

:)

Many thanks.

In the case of a cold/broken joint, I'll generally remove the old solder with braid or a 'solder sucker', then resolder with rosin-core solder.

The yellow transformer still emits a wee buzzing noise but with the rear cover on the electric panel it is not audible from the front of the oven.

I was going to test the output volts as Zeke mentioned as the info is started on the side of the unit but once the joint was identified, just focused on that.

I wonder if it was heat or the buzzing that broke the joint loose.

I used flux and if it did not help it sure did not hurt.

There was hardly any old solder to deal with. All I did was heat the pin and it was "gone" around the base. I just used the solder the electronics store suggested I buy. Don't believe it is cored. Came in a plastic tube that is long gone.

Now it looks like this:

http://forums.pelicanparts.com/uploa...1373203822.jpg

The transformer buzzing is not uncommon, I wouldn't worry over it unless the noise is bothersome.

What you found is typical when you have large pins from a transformer, or another heat producing device, soldered to a circuit board. The heating and cooling causes the device and pins to expand and contract, eventually causing the cracked solder joints, particularly if the joint did not have enough solder, or wasn't cleaned well before applying solder.

I've found that if there isn't too much solder on the existing joint, just adding some while re-flowing the joint will take care of the problem. If the joint already has a good bit of solder on it, using a solder sucker and then re-soldering the joint is best.

Nicely done! I have re-soldered and repaired amplifiers with similar results because I was too cheap to spring for a new board. Intermittent problems are often the most difficult to diagnose but the easiest to repair. Nearly always a loose wire/loose connection.

It's almost certainly multi-cored solder if you bought it from an electronics store, 'coz only plumbers/metalworkers use "real" solder with separate flux - and there would just no point for electronics work, unless you were soldering honking great heat sinks...

Does give a little puff of smoke when you tin the iron with it? If "yes", there you go; that's flux burning off; solder doesn't smoke when it melts :)

Solder on that board looks a little light/scanty - but pretty good compared to most of the 80's bosch electronics I've seen - amazed most of that stuff ever worked, much less worked for 25 years before it stopped working and needed to be re-flowed...