I need help to boot pls (broken button/old rom)

[néonaloj]

Hi,

I've got an old OP3 wich my son is using. The problem is that the power button is broken/not working. Last update was made years ago (maybe 4 or 5..), and there is "Tipsy rom" installed (Android 7.1.2 ).
So when battery is empty for instance, to put the phone on I had to put the phone on charge, and then the screen(s) appear(s) that it should "boot in 5 sec" (see attachments). It did work before, but doesn't anymore... ! Don't know why.. ?!
I've searched how I could do but I don't find an answer.
To be clear : adb is enabled but the phone isn't recognized (or only while in recovery) so I can't use code lines (I also tried in different usb slots / on different pc). And when I put it on charge, I still do have the boot screens that say "if no key pressed : your device will boot in 5 seconds", but instead the charge screen appears (with battery charging). I've tried to disconnect the battery, the volume button, the motherboard.. with always the same result.
Could someone please be kind enough to give me advice on how to boot the phone ? It'd be really appreciated !! Thanks.. !

 

[ze7zez]

It is difficult to assess the situation without carefully checking the operation of the switches, whether current is passing or not. If they are not damaged, the cause may be a defective electronic button controller on the motherboard.

Since it is currently not self-starting, there could be more causes.

I suggest replacing the switches with working ones. This will be the first,cheapest and maybe the only option for diagnosis.

 

[néonaloj]

It is difficult to assess the situation without carefully checking the operation of the switches, whether current is passing or not. If they are not damaged, the cause may be a defective electronic button controller on the motherboard.

Since it is currently not self-starting, there could be more causes.

I suggest replacing the switches with working ones. This will be the first,cheapest and maybe the only option for diagnosis.

Thanks for your reply !
I didn't test if current goes through because the battery must be get out to check it (I removed batteries before and had "bent" ones often). So you're right I don't know if it's the button switches/cable, or worse (contact/motherboard...).
That said, I would like to try to find a way to "force" boot, for exemple I've tried to hold volume button while/between/after boot screens appear, but yet I always come on the screen wich allows to choose from "power off, restart, recovery, fastboot mode"... (with volume button). I don't understand why it rebooted before (like the screen says "after 5 seconds") as it worked well before but refuse to now..
I appreciate your input, many thanks ! If you've another idea... ? . Thanks anyway !!