I got a Fairphone 4 after security updates were discontinued on my Samsung Galaxy S9 and I figured out it couldn't be flashed with a new OS (it was a fantastic phone while it lasted- was honestly Underutilizing its overall power. Got 5 years out of it).
TLDR : read the last paragraph
I am honestly taken aback by the transparency in regards to the FP4's construction. The repair manual gives the part number, quantity, and purpose of every single component on the PCBs. You get the full schematics as well.
Obviously I can replace any major part/board until support stops (they're saying they'll support it for 3 more years minimum), but I imagine that I could stock up a couple spare parts and treat the device well and get much longer from the hardware. As for support for the OS, I got the phone through Murena who put their own custom OS on it, but I imagine I could flash a new OS onto it without much problem.
The things I am thinking about are past that point. If replacement parts no longer get sold and something fails on one of the boards, I don't know the feasibility of finding a replacement component. Like, I imagine getting a matching capacitor wouldn't be an issue, but can you even find a replacement snapdragon or WiFi chip? And while we're talking about hot-air soldering on replacement parts: do PCBs have a duty lifespan? Is it more likely that my screen'll just die long before anything else?
Basically, assuming I treat this phone right and don't break anything in a drop, how long can I glide this fella out? what's the shorest lifespan parts that'll fail first - and what kind of lifetime can I suspect? What are parts I could consider replacing with a similar part? (I own a 3d printer and do diverse material fabricating as a hobby).
The first component that will definitely fail is the battery. They usually don't last for more than 5 years (can even be 3 years on powerful hardware). Sometimes the SoC (CPU) can fail, especially if used at high temperatures very often. But that's not very hard to repair. The thing you should be worried about is software support. Though idk much about it on Fairphones. You can probably expect 5 or 6 years (since the launch) of custom ROM support. Also the memory will degrade and lose its speed over time. Repairing it is not a great idea so you may need a new motherboard in that case
The battery failing makes sense to me. I imagine that's the easiest thing to replace non-conventionally - especially since you can hand-swap batteries on fairphones. I think it's possible I could find an aftermarket battery of similar parameters.
Past custom ROM support: could I build a linux ROM for it? Is that something reasonable to aim for?
I didn't know you could fix a failed CPU, that's surprising news to hear. What's that usually entail?
Could replacing the memory on the motherboard be possible/feasible with a standard hot-air rework setup?
Both CPU and memory replacements are not easy. In case of a failure of these components in a smartphone it is considered a better idea to replace the whole motherboard
As you can see, fairphone still sells spare parts for the fairphone 2, that came out years ago (i think ~8?). So as long as fairphone isnt going bankrupt you have a good chance to get any spare part you need for years to come.
Better read the link before you post. Most stuff for the fairphone 2 is listed as 'discontinued'. I bought my FP2 like a few months before the FP3 came out, and they killed the spare parts sooooo fucking early. My mic module broke, and I had to throw away the phone. Did get a few years, but not really worth it. Will probably never buy a FP again, the company is too unreliable on spare parts.