Macbook Pro 13" A1989

[247it]

Hi all, I picked up a MacBook pro 13" with a A1989 mainboard, it suffered a little liquid damage around the CPU power section,
USB C switches to 20V 0.17 amps, this rises to .6 amps, stays that way for 30 seconds or more, then drops to 0 amps, 20V is maintained, fans spin at full speed for 1 second then the cycle starts over, CPU warms up slightly, mosfets U7210 heats to 38C and U7220 briefly heats and then goes cold at the start of the cycle,

Could anyone point me to some posts on what voltages to check and where / how to check for shorts and the places to often check?

Many Thanks for your help.

[mon2]

MacBook Pro A1989 - Repair Wiki

[247it]

Thanks mon2, ill work my way through

[247it]

Everything checks out fine, no shorts and voltages are all stable, I saw a post of yours MacBook A1989 missing rails PP3V3_S5 and PP1V8_S5 - Badcaps my trackpad is very liquid damaged, im guessing this could be the problem?

[mon2]

Suggest to test with a known good unit. You can try Mobile Sentrix (UK) who recently opened up a branch in the UK. They have been solid to supply Aliexpress type of pricing and products. Best is that they will allow returns as well. Alternatively, you can try Amazon and return it if the part is not required.

[247it]

Thanks for the advice, Amazon have them for £20, the main board ribbon is also toast, one of the pads has rotted to nothing

[mon2]

Ouch. Amazon also is selling the replacement cable? Great if they do.

[247it]

Hi mon2, thanks for your help,

I managed to get a like new track pad and ribbon for £10, not too bad, i also picked up a drilled but tidy doner board for £13, so have some spares, I have replaced the U9000 chip as i poorly reflowed it a year ago (last time i worked on the mac) but still the same,

its a long shot but you may know what the below means,

Power meter starts at 5V then jumps to 20V - current climbs to 600ma and stays stable for a while, then the amps jump to 800ma, reset then happens immediately, meter reads 0 amps 20V and the cycle starts again, any idea what happens at 800ma?

[mon2]

Someone is heating up and then all power cycles. Remove all power. Meter in resistance mode. Measure the resistance to ground on each and every inductor on the board. Report any suspects. A thermal camera will help to check who or what is thermally throbbing on the board.

[247it]

Lowest coil resistance to ground is 6 Ohms, highest is .5M, does that seem like CPU is ok?

three things get warm,
CPU heat sink,
U7210 @ 40C, (replaced it, still warms up)
U7270 briefly (1sec) warms while CPUSA_DRVH is at 4.4 volts (replaced U7270 also)

[247it]

So, im thinking a something starting or a power rail being created into a short is causing a protection condition, im not seeing heat because the protection is very rapid, so would anyone know what power rails to check further down the line that would cause a complete power cycle? if i can find the rail i may be able to inject an appropriate voltage and current to identify the short, or is this a bit simplistic.