Chosen Solution
I know the 4S is old now but I’d still like to get the phone working as an emergency backup. I’ve taken the back off and measured the battery with a multimeter and it measures 0V but I suppose that’s not surprising as the phone hasn’t been used since it stopped working over a year ago. With the charger connected I measured the left and right pins of the battery connector in the actual phone and it measured 1.15V, not enough to charge the battery. My guess is the dock connector is ok or I wouldn’t see 1.15V. Does that sound right? If my guess is true then perhaps it’s the logic board that’s at fault. I’ve measured continuity through L3 and L4 but have not worked out how to get access to L28 to test it. How am I doing so far, does the above sound right? Thanks for reading
Are you able to get apple logo boot looping with battery unplugged at least? If yes then I recommend trying another battery if the battery has been dead flat for a year or more. With iPhone 4 or 4s batteries when dead flat for a long time they need to be jump started with a external battery charging fixture because for some reason the iPhone 4’s don’t support charging completely dead flat batteries, you would end up seeing the battery logo boot looping constantly as a result. Have you checked if it’s just the screen connector cables that have gone loose? It’s a common issue for the LCD cable to pop out unplugged for iPhone 4’s with replacement screens.
I would be thinking dead battery , the 4s are getting quite old now and common for battery faults, if this was working fine before go down path of checking charge port making sure pins are clean a sharpened tooth pick is good for clearing out dirt from charge port if that does not help change battery.
