Here is a new approach to this repair which I am contemplating:

• The original ribbon will be used and a new trace will be drawn on it on its outside. This new trace will then be covered with some sort of protection like UV glue. (This allows the original pcb connector for the ribbon to be reused. In retrospect this is how this repair should have been attempted in the first place. There was no need to peel off the electrical sandwich layer of the keyboard membrane.)
• The silver traces on the keyboard membrane will be drawn back and gaps filled. Where the ribbon connects to the traces on the keyboard, the new ribbon traces will be joined to the silver traces of the membrane. Silver traces are exposed and it appears that they can be used in this manner (but this is not true of the brown traces that act as jumpers, for those the steps further down this list will be used).
• After the above 2 steps are completed all traces have to be checked for good continuity.
• The dots where the silver and brown traces are connected to each other get a good size circle of conductive trace.
• Where the dots are on the keyboard traces, a punched hole is made in the torn pieces of the membrane.
• The torn piece of the membrane is then glued back to the rest of the membrane.
• To recreate the brown traces new traces are created on the outside of the torn (now glued) piece. These new brown traces created on the outside of the insulating layer, are connected to the silver traces at the punched out holes. These newly created brown traces are then covered with protective glue such as UV glue.

This is not an easy repair but it may be possible and can be low cost.

The materials used can make or break this repair. The protective and insulating glues and the conductive glue are the main parts needed and they have to not only be suitable for the application but come in proper applicators so that traces can be drawn precisely. This is where the members of this forum may be able to help by suggesting products or DIY methods to acquire these parts. Thanks.

I wanted to type this new repair procedure and put it out here to get feedback and to reinforce the concept for myself. So your feedback and suggestions are helpful. Thanks.

 

You know where I stand, so ‘nuff said.

 

How durable the conductive ink/glue would be is unknown.
I admire your staying power, but if it were me I'd abandon the membrane repair and adopt the approach Wayneh suggested many posts ago. Even if tact switches are less reliable than membrane ones as Anniel says, and repeated replacement were necessary over the years, the effort (and probably expense) involved in keeping the oven working would be less.

 

Here is a new approach to this repair which I am contemplating:

• The original ribbon will be used and a new trace will be drawn on it on its outside. This new trace will then be covered with some sort of protection like UV glue. (This allows the original pcb connector for the ribbon to be reused. In retrospect this is how this repair should have been attempted in the first place. There was no need to peel off the electrical sandwich layer of the keyboard membrane.)

That's what I said in the first place, repair the ribbon cable first before going any further as that might have been the only thing wrong with it.
Chances were that was what was stopping the oven off button and nothing else.
It was total madness ripping it apart before doing that.

 

Appliance control boards fail largely due to a few reasons:
1. Cold solder joints to connectors and relays, some cause fires and product recalls. Use a magnifier and inspect all high-current soldering and touch up as needed. T1, T5, T18 look not great.
2. The electrolytic capacitors age and dry out. Appliances usually have power on 24/7, so 8,760hrs a year. Worse if the part sees some local heat from nearby power resistors, the power transformer or the oven heat.
3. Relays go bad, the contacts wear out.
4. Power line surges
5. Cheap designs with planned obsolescense to make you buy a new oven.

I would certainly agree with all of these, particularly design.
It must have started life as a decent prototype with decent components.
Over time and iterations, the designers would have looked at every component to see where costs could be cut. If the board production was farmed out to another company, they would do the same.
You end up with a board that works, but only just. It would be tested to maybe last as long as the warrantee, i.e. not very long.
In my limited experience of domestic stuff, dishwashers, washing machines, gas heating boilers, TV's etc., it's almost always the "board" that fails.
You get someone to look at the boiler - "it's the board". Solution, replace it with another crappy board and so on.
Designed to work for a reasonable length of time, not to last and be reliable.
I designed equipment for use in remote field locations and in processes that had to be reliable.
The approach was quite different, every component was as high quality as possible, good spec then 50% extra on top.
Designs could not rely on components that could not be sourced easily.
We used a lot of PLCs - Siemens, Mitsubishi, ABB, all good solid stuff.
The bottom line was, if something went wrong, I usually had to fix it, so everything was designed to be easily replaced - I specified it right down to the exact type of nut and bolt used - 316 stainless usually.
Another aspect is safety.
I've seen the two appliances, a washing machine and a dishwasher (Philips and Bosch) catch fire. The dishwasher wrecked the kitchen.
Dishwashers are inherently unsafe. Controls and wiring in the drop-down door, wiring constantly being flexed.
If I had the time, I would design my own appliances, using high quality stuff and where necessary, write the software as well.
And keep a good stock of spares.

 

I'd be leery of eBay - too many counterfeits. You can say the same about Amazon but my last order of capacitors was from Amazon - I couldn't resist the price. Note that I stuck to a premium brand, in this case Panasonic.
https://www.amazon.com/gp/product/B073YQB9X2

The reliable supply houses are Mouser, DigiKey and Newark. I prefer the search tools at Mouser.

Second that.
Not forgetting RS.
DigiKey have fantastic in-depth levels of stocking. Couple that with UPS delivery, couldn't be better.
I do a bit of coding, mainly through Arduino.
How often you see "doesn't work".
Dig a bit deeper, "it's a clone I bought eBay or whatever"
You bought cheap, you got cheap, plus you like to use all the Arduino resources, but you don't like to put your hand in your pocket to buy genuine Arduino.
Not a lot of sympathy.

 

That's what I said in the first place, repair the ribbon cable first before going any further as that might have been the only thing wrong with it.
Chances were that was what was stopping the oven off button and nothing else.
It was total madness ripping it apart before doing that.

Repairing ribbon cable?
Can't be worth it. Replace, surely.
What I find on stripboard prototypes, is that any wire links, i.e. thin insulated interconnects, is the solder joint is the weak point, not quite so much with plated through holes.
Any slight movement will start the detachment process.
What I do now is fold the stripped wire on the track side back and solder it to the track so it can't twist.
Not forgetting a decent flux even if it is cored solder.

 

Repairing ribbon cable?
Can't be worth it. Replace, surely.
What I find on stripboard prototypes, is that any wire links, i.e. thin insulated interconnects, is the solder joint is the weak point, not quite so much with plated through holes.
Any slight movement will start the detachment process.
What I do now is fold the stripped wire on the track side back and solder it to the track so it can't twist.
Not forgetting a decent flux even if it is cored solder.

Soldering low cross-section stranded wires is a no-no for me. Anything less than 0.25 mm² will break - rather sooner than later - at exactly the location where the solder stopped flowing into the wire. Larger cross-sections are less prone to breaking, although this depends on the amount of bending exerted. And soldered 0.14 mm² wire break more or less from looking at them
Stranded wires of low cross-sections should always be connected by some solder-less means - crimping or one of all these IDCs (isolation-displacement connectors).

 

Soldering low cross-section stranded wires is a no-no for me. Anything less than 0.25 mm² will break - rather sooner than later - at exactly the location where the solder stopped flowing into the wire. Larger cross-sections are less prone to breaking, although this depends on the amount of bending exerted. And soldered 0.14 mm² wire break more or less from looking at them
Stranded wires of low cross-sections should always be connected by some solder-less means - crimping or one of all these IDCs (isolation-displacement connectors).

Agreed.
Other than stripboard prototypes, I wouldn't use it as a method either, but it doesn't stop commercial operators doing it.
After all, why spend out on Molex, JST, AMP crimps and IDCs when a dollop of solder does the job, for a while.