fixing ribbon cables for oven

[engineheat]

The control panel on my oven doesn't work right. Initially, only certain keys are not responsive, now it's most of them, rendering it useless. I heard it may has something to do with the ribbon cable connection going bad.

The ribbon cable is this type:


As you can see it's very thin and filmsy, and it goes into those connectors on a PCB. Do you think the problem is most likely due to the ribbon cable connection? Or could it be the PCB itself being bad.

I'm thinking about testing the connectivity on the ribbon cable where it goes into the connector with a meter, and I might "fortify" those leads with some wire glue.

Thoughts?

[Wendy_Preston]

What you've got there is a Flexible Printed Circuit (FPC), not a ribbon cable. And that's going to go into an FPC connector on the board. There are better experts than me on this forum, but I expect they would be keen to see the state of the connector that this plugs into. Also, a picture focused on the very end, and also the underside of the end would be useful pictures.

It might have just got dirty - how old is the oven? The connector might be contaminated or dirty on the inside too - maybe some experts on here have some ideas how it can be cleaned up. It's not something I've ever had to consider, sorry.

The track on the right looks damaged - is that a hole, or just shine?

[Ian.M]

Start by illuminating the flat-flex from behind with a diffuse light - a lightbox with enough sheets of paper over it to kill the glare is ideal, and check with a magnifier for any cracks in the traces near the connector and anywhere else there is a sharp bend in the flat-flex.

From the photo, I suspect the trace on the right is broken where it goes into the connector.  Follow it back to the keyboard matrix and see if it goes to the bad keys.

For repair:

Conductive paint is useless if the substrate is cracked.  You might get somewhere with two tiny dabs of conductive epoxy to connect a strand of very fine tinned copper wire across the gap.

*SOME* flat-flexes with copper traces are solderable.  Ones with printed conductive ink traces or low melting point substrates are not.  If it is solderable, a single strand of very fine tinned wire, and minimal dwell time on the joints is your best hope of bridging the crack.  Don't go more than a minimum distance up the flat-flex as you need to keep as much length as possible for the next option.

Depending on the slack in the flat-flex, it may be possible to cut off a damaged end and scrape back the insulation on the traces of the fresh end to expose them for the connector contacts.   

Contact cleaner spayed into the connector, and onto a slip of cartridge paper the same width as the flat-flex inserted in the connector is the best bet for cleaning its contacts.  Pull the paper out to get a wiping action across the contact faces.  If the connector has a latch, don't close it all the way - you don't want to tear the paper or distort the contacts.  If you see dirt on the paper, repeat with a fresh piece until it comes out clean.