Apple iPad Air 2 (A1566) - Seems to be power cycling, no display, new battery/Tristar

[Aimbit]

Using an ammeter, original battery was only taking 90mA or so... then down to 0, up to 90mA, down to 0, etc, in a repeatable pattern. This iPad was very old, so first thing I did was swap the battery for a good one, and it came pre-charged. The old battery had negligible voltage.

Now the iPad go up to about 1.5-1.6amps charge, then it drops to 0 after a few seconds... rinse/repeat as before. I tried changing the Tristar chip to see if that would help (and also my first real BGA chip!) but it seems to make no difference. Where should I look next?

I should poke around the board for shorts or something. I'm guessing some kind of safety is kicking in that is rebooting it continuously.

[Aimbit]

So I connected it to USB power and just had a look with a thermal cam... looks like the SDRAM is spiking up to nearly 70c immediately while everything else remains cool. So perhaps the SDRAM is bad. Swapping these seems like a major pain in the ass as it is surrounded by microscopic caps and is glued to the board with that gunk they use.

[mon2]

Share a normal but clear pic of the same area.

[Aimbit]

Share a normal but clear pic of the same area.

added.

i checked around this area as best I could for shorts and didn't really come up with anything. Definitely some very low resistance spots, but they are >1ohm, not sure if that necessarily is short or not. I think ram areas are normally low resistance? Still kind of learning this stuff.

fyi the two capacitors at the bottom of the ram chip that look kind of black are just discolored from the black glue stuff they put on the chips, they measured fine.

thanks

[mon2]

Will check my database but believe the resistance for the ram is too low.

[Aimbit]

Will check my database but believe the resistance for the ram is too low.

any luck? Thanks

i thought it kind of strange that only the ram shoots up to 70+ and the board doesn't even really power on. Seems like it's triggering a safety to turn off with its power cycling.

[mon2]

Power cycling will be from the local power rail that feeds this component that is heating up. When the part heats up, it is abnormal to see such a high temp which means excessive current draw and this causes a larger than normal voltage drop for the power supply regulator. The current sense resistor will observe this condition and then powers down so the 'chirp cycling' begins. Turns on -> gets hot due to high current draw -> turns off.

[Aimbit]

Power cycling will be from the local power rail that feeds this component that is heating up. When the part heats up, it is abnormal to see such a high temp which means excessive current draw and this causes a larger than normal voltage drop for the power supply regulator. The current sense resistor will observe this condition and then powers down so the 'chirp cycling' begins. Turns on -> gets hot due to high current draw -> turns off.

Right. Ok. Well I guess I'll try swapping or maybe just reballing the ram and see what happens! This is mostly for fun/education at this point… Air 2 is pretty old at this point.

thanks