I installed the custom rom e/os 1.0 stable. I unlocked the bootloader and I locked again the bootloader without problems. e/os 1.0 stable works very well on my FP4 but I encounter an issue. Now, when I press during a long time the volume down button (the FP4 is power off), nothing happens (the screen is still black). I power on the FP4 and rapidly press the volume down button, and the bootloader screen doesn’t appears, it is the e/os loader who appears. So, I can’t access to the bootloader screen manually with the phone buttons. Does this issue come from e/os because I didn’t encounter this problem before (when I was on Fairphone OS with the bootloader locked) ? What’s wrong ? Have you got an idea ?
Note: I think there is a bug (e/os ?). I tried volume down button + power button and then volume up button + power button during a long time and the Fairphone logo remains (no fastboot and no recovery mode). I released these buttons and the e logo appears.
I’m thinking that if a cable for charging has resistors across the power lines then the phone will be able to respond as if it were negotiating with a charger and effectively ‘turn on’ as if to charge. However if the cable is an older straight through type with no such included resistors it will not work as in point 2.
I doubt the mere presence or pressure of the connection will give any signal to the phone. Mind you, there may be no such cables, or at least in modern circulation. Just checking the theory.
I don’t think the cable matters in this scenario.
Every cable capable of charging the phone will turn it on and since this is basically just a fancy way of pressing the power button I don’t see a reason this schouldn’t work.
Edit: I checked the cables / chargers I have lying around and so far they all work
Thanks to all for your help. I followed the tips from hirnsushi and the usb-c cable is necessary if I want to use the volume down button only to access bootloader screen. I wrote the tip down on a piece of paper to remind myself later. So, I installed e/os correctly because the device state tell me ‘locked’. Now, I can use my phone with the new custom Rom.