820-00840-A PP3V3_G3H at 2.26V

[Jenzo]

Hey everyone,

Long story short;
No PP3V3_G3H
PPVIN_G3H_P3V3GH was way too low, turned out to be C7078

Now my PP3V3_G3H is at 2.26V, and I honestly have no clue where to look.

Removed R6999 to check, I have 3,3v coming from PP3V3_G3H_VR. Does this mean U6990 is good for sure? Or what should I check to find the cause of this voltage drop.

Thank you in advance!

[mon2]

Re: 820-00840-A PP3V3_G3H at 2.26V

hi.

Does this mean U6990 is good for sure?

Yes.

With R6999 out, you have isolated the voltage rail provider (left side) and the voltage rail consumer (right side) of the logic board.

Remove all power.

With your meter in resistance mode, check the resistance to ground on R6999, pin 2 pad. You must have a low resistance here as the voltage rail tanks when R6999 is soldered back.

What is the resistance on the pad to ground ? Since 300mA is max for this dc-dc switcher IC, the present load must be consuming > 300 mA to droop to 2v26.

[Jenzo]

Re: 820-00840-A PP3V3_G3H at 2.26V

Hey, sorry took a while to get back to you, was out sick for 2 days.

600mA on pin 2. What would be the best way to find out what's causing this? As far as I can see on the schematic/boardview there's a lot on this line.

[mon2]

Re: 820-00840-A PP3V3_G3H at 2.26V

Go here and find your logic board. Then place your meter in diode mode. Remove all power.

Then place the RED meter to ground.

Measure each point (BLACK meter lead) noted in the following webpage for the diode reading. Compare against the posted known good diode value.

https://logi.wiki/index.php/MacBook_...e_Measurements

Aside from the above, I would recommend using a power supply to inject a low voltage on this rail to see if there are shorted caps. Others may have better suggestions. Be sure there are no obvious liquid shorts that may be causing this excessive current draw.

Since this rail is 3v3 if normal, the injection should be lower than this value like 1v0. If you have a thermal camera, it is possible that this process will show the problem as a heated part. Alcohol dabs with q-tip also works well - as the part heats up, the alcohol will evaporate quickly as compared to normal parts.

Again, only my suggestion but let us wait to learn more about your logic board with the diode readings.

On the voltage injection, let me link a good video on this topic. Will update this thread after locating the one we used to learn from at the shop.

https://youtu.be/EWuzmIz7hOE

NB: If you do proceed with this method, keep the voltage lower than the 3v3. Recommend 1v0 and only slightly increase if required to locate the possible shorted capacitor / part. For now, start with the diode readings.

[Jenzo]

Re: 820-00840-A PP3V3_G3H at 2.26V

Thank you for the info, I had no idea of this wiki's existence. This will be of great use in the future.

So, the diode mode readings gave nothing out of the ordinary. On average they were a little bit higher then the example on the wiki, but this is probably because I'm using a cheaper multimeter. (Or because the measurements on the wiki are taken on a 820-00875, although it should be the same as the 820-00840). I'll take my good one from work coming Tuesday just to make sure.

I have tried the voltage injection as well, at 1v, 1amp, but it took 0amp. Assuming this is because I don't have a direct/full short to ground?

Really appreciating you helping me out by the way, this is learning me a lot.

[Jenzo]

Re: 820-00840-A PP3V3_G3H at 2.26V

I had the idea it might have been the U7000 (ISL9239), replaced it, problem remains exactly the same.

One thing I've noticed is depending on which usb-port I plug in the charger, either PP3V3_UPC_XA_LDO or PP3V3_UPC_XB_LDO will be at 2.26v, and the other one steady at 3.3v. Might this be a hint to where the problem might be?

[Jenzo]

Re: 820-00840-A PP3V3_G3H at 2.26V

Finally figured it out. U7000 and D6905 were a problem. Replaced them both, have a fully working board now. Thanks for helping!