820-3476 MacBook Pro will not charge or run off the battery

[Flippers McCoy]

Hello, everyone!

I have an 820-3476 motherboard that works fine, except it won't charge or run off just the battery. When I have the battery plugged in and boot it up using an adapter, it can see how much of a charge the battery has, but it's condition is Replace Now and says "Power Source: Adapter" and "Battery is not Charging."
I tested the battery with Coconut Battery and it's at 88% design capacity. I tried the battery in a known good computer and it worked fine (meaning I also have a known good board to compare with, should that be helpful). When I plug in just the battery into the bare board, PPVBAT_G3H_CHGR_R bounces all over the place between 4V and 11V, and CHGR_BGATE goes all over the place too fast for me to see a range. If I leave the battery plugged in and then plug in the adapter, PPVBAT_G3H_CHGR_R is between 12.56V and 12.59V and CHGR_BGATE is a solid 12.55V.
I checked R7150 and it's getting continuity to it's respective pins on U7100.

Any ideas on what I should check next?
Thanks a bunch!

[Flippers McCoy]

Re: 820-3476 MacBook Pro will not charge or run off the battery

Update: Turns out if I leave the battery plugged in for a while, PPVBAT_G3H_CHGR_R ends up staying at a solid 11.57V, and CHGR_BGATE stays at 4.79V

[Flippers McCoy]

Re: 820-3476 MacBook Pro will not charge or run off the battery

No pins on U7100 are shorted to ground, either

[SMDFlea]

Re: 820-3476 MacBook Pro will not charge or run off the battery

Have you checked Q7155

[Flippers McCoy]

Re: 820-3476 MacBook Pro will not charge or run off the battery

Q7155 looks pristine and seems to let power through properly, I don't think anything is wrong with it

[BlueMidnight]

Re: 820-3476 MacBook Pro will not charge or run off the battery

The thing that strikes me is that PPVBAT_G3H_CHGR_R bounces around as low as 4V. But because of the body diode in Q7155, PPVBAT_G3H_CHGR_R should never be more than a diode drop lower than battery voltage. Even if Q7155 were completely turned off.

The only time you mentioned seeing Q7155 working was when you let it sit there a while (the gate voltage must go low to turn it on). So it's not completely above suspicion yet. But, the type of failure that could explain what you're seeing is a bit too bizarre to put near the top of my list (it acting like it doesn't even have a body diode, but then miraculously being able to turn on after sitting there).

But, what about the battery voltage itself (PPVBAT_G3H_CONN)? Is that just as unstable?

Perhaps something related to the SMBus or commands sent/received over same is wonky. Or the battery doesn't see the 0V SYS_DETECT_L signal that lets it know it's plugged into a board and it's okay for it to go ahead and output voltage. Or there could be an issue with the traces or battery connector itself. Etc, etc.

[Flippers McCoy]

Re: 820-3476 MacBook Pro will not charge or run off the battery

So I went back to test PPVBAT_G3H_CONN and it's stopped fluctuating like crazy the moment I plug it in and gets a solid 11.57V. When I plug in the adapter at this point the voltage on PPVBAT_G3H_CONN, PPVBAT_G3H_CHGR_R, and PPBUS_G3H slowly rise from 11.57V to 12.37V and stay there as the fan spun.
To make sure it wasn't a fluke I disconnected everything from the board and made sure the power drained and then hooked it back up, still not doing the fluctuating thing anymore >.>
I put it back together enough to test it in the OS, and it works fine now. I guess getting a good nights sleep was all it needed?

One thing that I forgot to mention but may be related is that R7185 and C7185 had a small amount of corrosion on them when I first took the computer apart, but after cleaning it looked great and tested fine.

Thanks for the help everyone, I appreciate it

Edit: If anyone has any insights on how R7185 and C7185 might cause these symptoms, I'd love to hear it!

[StephE]

Re: 820-3476 MacBook Pro will not charge or run off the battery

Hello,
i have a board showing the same symptoms here.

Did you ever find the faulty part(s) ?

[Flippers McCoy]

Re: 820-3476 MacBook Pro will not charge or run off the battery

Did you ever find the faulty part(s) ?

This was a while ago so I'm a little hazy as to the details, but as far as I can remember the computer just started magically working again after being left in the shop overnight. You win some and you lose some I guess!