So, just to sum up, my issue is definitely a problem on the core module contacts as told by AlbertJP (see here ). It’s a long thread (>200 posts). I summarize here what I understood after a thorough reading.
It looks that it’s an issue with the fact that the core module plastic plus removable parts it’s not super-rigid, and it ends up being affected by mechanical changes due to temperature, humidity (people reporting it stops working after going to Thailand) or pressure (people reporting it happens after a flight) or physical changes (after dropping the phone). This somehow affects the connectors on the core module with the display. It is not the display connectors, but the core connectors. Myself and others replaced the display and the problem persisted.
Anyway, once the core module connectors become unstable it keeps this way for most of the people I’ve read.
I wonder if this is one of the reasons for FP3 not being as much ‘removable’ friendly anymore. I mean, it is still removable but you will need a screwer for any access, and the core seems sturdier.
Temporary mechanical solutions that work for a while (from minutes to hours to sometimes days):
- Apply gentle pressure by hand, or by a cardboard/sticker on the cover. This is not adviceable as it could eventually bend the connectors. That was my case.
- Remove the pressure (usually after days of applying pressure) may make it work for a while too. That also worked for me.
- Bend back to vertical the connector pins, in case the pressure was not so gentle or applied for several days.
- Clean the display module/core contacts. Only with 96% alcohol. Do not use contact sprays or anything else. Do it with a soft cloth, never scratch. This never worked for me anyway.
- ‘Twist’ the phone. Hold it at the bottom and twist the upper part a little worked for me. I only tried this after checking that the phone was a little twisted, by putting it on a table and testing that it did not rest over its four corners equally.
- Clean and maybe push/bend out (towards the screen) the silver contacts (see here)
Any of these ‘mechanical’ solutions may last longer if you keep your phone away from mechanical stress:
- Do not put it on leg pockets or other places where it can be ‘twisted’
- Do not put it on, let’s say, backpack pockets where it can be more affected by temperature changes.
- I think the internal pocket of the jacket is the perfect place, if it’s not a tight jacket.
- Do not use it for long or for highly computational tasks (e.g. gaming or reading an ebook) as it may heat the board and become stressful.
I know that having so many cares can be annoying and not anyone would be happy with it.
Then, there’s the oven solution. Risky and difficult. I don’t feel confident to try this by now. Also, it seems you should not try it on an oven where you cook food (I don’t have another one). This looks like solving the problem for sure (at least, for longer) OR destroying the phone for sure.
Hope this is an accurate and summarized picture of the lore a lot of wiser people has gathered over years.