Membrane Keypad Repair for Wall Oven

[dmilamj]

I have a DCS WOS230 wall oven. During humid weather, the oven display will show a F7 error and there is a continuous beeping from the controller. The F7 error is a "continuously depressed key" error.

I have unplugged the keypad ribbon cable from the controller and reapplied power to the oven. There is no error generated in this case. This eliminates the controller as the problem, and isolates the problem to the membrane keypad.

I bought the oven used/scratch and dent, so it there is no warranty.

I haven't been able to identify which key is at fault, but since a replacement (only sold as a keypad, controller, and clock module) is about $450 I would like to try to figure it out and fix it if possible.

The oven is fairly new, and there is not much wear on the keypad. I think that the top membrane layer must have gotten stretched in installation or something, and causes a short.

Does anyone have any experience peeling a membrane keypad apart and repairing a short?

Is a membrane keypad generally equivalent to a bunch of momentarily depressed switches?

Can I check continuity across the ribbon cable pins with different keypad buttons pressed to find out which buttons correspond to which ribbon cable pins? I don't have any idea what the pin out is for the ribbon cable, and I don't even know if there is a single ribbon cable pin for each button, or if the cable is double sided...

I am tempted to make my own control panel, since it's basically just about 15 momentarily-on buttons and a keypad. Then I could arrange them in a more logical manner, and attach the clock/controller behind a panel cutout.

Thanks for any comments or assistance!


Dave

 

[duke37]

Dave,

If it occurs in humid weather, it could be condensation causing a short in the control panel.
Could you put in some silica gel to absorb the moisture or warm it up slightly to evaporate it?

Duke

 

[dmilamj]

Good suggestion, I will try to warm it up this evening with a hair dryer/heat gun and see if that will take care of it.

I live in Houston, and humidity is more common than dry air, by a factor of 10 or so.

 

[(*steve*)]

There could also be some foreign matter stuck in the keypad which gets slightly more conductive with humidity.

 

[dmilamj]

So I tried warming up the membrane switch with a heat gun tonight. I'll see how that works.

While I had it apart, I tried to figure out how it works with no luck.

I was testing the continuity between the ribbon cable pins while pressing a key. I thought that pressing a key would cause a short between some of the ribbon cable pins, but I couldn't find any continuity between any pair of pins to save my life.

Does anyone know how these membrane keyboards work, normally?

There are 17 ribbon cable pins. There are something like 15 buttons on the keypad, and then an additional 12 key number-pad. There must be some pin sharing or perhaps matrix style pin addressing going on.

I'll post some pictures of the control panel tomorrow.

 

[dmilamj]

Front of the keypad/control panel

Back

Back detail showing membrane switch traces

Back detail showing membrane switch traces

Back of controller/clock

Controller/clock

 

[(*steve*)]

If you're getting an error saying that a key is stuck down, then the possible issues are:

1) a key is stuck down
2) some (possibly temperature or humidity dependant) gunk is caught in or near a key.
3) there is a cable fault
4) there is gunk on the controller causing something similar to (2)
5) there is a controller fault
6) there is a display fault that causes this error to display
7) there is another reason for this error

Looking at your pictures, everything seems clean, so I'd tend to discount (4). (6) and (7) are either very unlikely or really hard to figure out, so forget them. I would think that (3) is unlikely, as a cable fault would be more likely to exhibit itself as an open connection, however there is a small possibility of a problem with the connectors at either end.

That leaves 1, 2, or 5 with a possibility of something going on in a connector.

You probably need to open up the keypad if you can and examine that. Unfortunately, there's lots of buttons and no indication of which one is the problem. I'd be looking for signs of something that seems out of place...