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Modello fine 2011, A1278 / processore i5 2,4 GHz o i7 2,8 GHz

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How to replace the CMOS / PRAM supercapacitor by battery?

Hi there,

As some of you may have read my previous MiniDisplay Port doesn't work; one chip stays warm during sleep.. I got a water-damaged MBP where an unknown chip stays active and hot during sleep. It discharges the battery much faster than it would do otherwise, but the other problem I discovered is that time and date settings are lost and reset to 2008, presumably because the main battery is too drained to maintain the Is there no CMOS RAM battery on this model?'s charge. Even if the machine is set to use Apple's NTP servers to sync back the time, having the wrong date means certificates are not recognized, and that wither the browser or Mac OS X refuse connection on invalidity grounds, preventing time to be set properly. An annoying catch-22.

According to the only shop that does this kind of repair, replacing the burned chip is just too dangerous for the computer to be worth it, on an otherwise working machine. It's a 40-pin QFN package, very close to other tiny components.

The other option would be to replace the supercapacitor powering the MBPs without a removable battery by a standard 3V battery to power the PRAM and SMC, and add a physical switch to disconnect the main battery while hibernating. Sounds like a less risky alternative as only two solder points on the board would be required.

The question would be: where is the supercap holding the charge for the PRAM and SMC on a Late 2011 MBP?

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Update (02/11/2018)

An update on an old thread: the main battery is now at 3.4% capacity and I am, again, at a crossroad. I suspect the few times I left it sleeping while forgetting to plug it in took their toll by draining the battery further than it could recover from.

The RTC chip (Silego SLG3NB148V) CAN be powered by a 3V coin battery through pin 13 (page 26 of the board schematic: match with similar part Silego SLG3NB114, page 11), it just isn't installed, and no provision is made on the board for such a battery. The "chip that doesn't sleep" is U9310, and marked as "Critical" on the schematic. What does that mean exactly? That it can't simply be removed and have the computer still working?

I found one mail-in repair service in Tennessee that claims to do "most"repairs between $75 and $125US, but still unsure if they would do mine as I'm far away from their shop.

To get the laptop back in proper working order, I'd be looking at a rather hefty bill:

replacement battery $80

repair existing motherboard: between $100 and $400, depending on shop and custom fees.

swap faulty motherboard for one taken from a Mid-2012 A1278 model in order to gain performance (Swap USB 2.0 for USB 3.0). I checked, they are screw-compatible. $500+, more so if I'm unlucky with customs.

And maybe get about $60 back selling the current faulty board?

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Show a picture of the burned chip and what do you mean the only shop that does this repair??? That is fairly easy repair (qfn) for what is today alot of shops that do component work. I pull them on off in 5 seconds and reuse solder on them tracking shorts etc everyday. You need to find some Macbook REAL motherboard repair shops. I would like to see the burned chip if you can I'm thinking replacing U2800 the RTC clock signal chip or the RTC crystal might do the trick but that's just a first guess. Your less risky idea won't work making a switch to turn off the battery will only shut the mac completely off which would be so risky it could catch on fire never do any modifications to a lithium battery!!


Apparently no shop is doing component-level work in my city. Only full motherboard replacements.

Why would I have to replace the RTC?


Who told you about this unknown chip ??? The problem sounds more in the battery charging QFN . There are a slew of mail in repairs on ebay pick one with great feedback and great reviews.

Would really like to see a picture of the chip if you can take a snapshot and upload it.


Mail in repairs are also extremely expensive, 400$+ s&h + insurance + conversion rate = almost more economical to buy a full motherboard.

I still don't get the point why an HDMI-related chip would also hold the RTC function, nor how it would allow me to replace the presumed supercapacitor powering it by a standard battery.



I can't see the picture I think it was uploaded wrong. I know that a HDMI QFN is not going to drain the battery. Sounds like you have battery charging circuit problem as well as the HDMI QFN.

But the answer to the question is the short needs to be removed on one or both chips. You will NEVER be able to power the SMC on with a 3v battery.


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There may be other things going with your mac that will need professional motherboard repair.

There is no super capacitor on the motherboard that capacitor that guy is talking about is a capacitor inline of PP3V3_G3_RTC the RTC circuit. The work around for your idea will not work there is no way to power the SMC with a button cell battery the chips design does not allow this. If you don't want to spring for the high repair sell the board in it's state now and use the money towards a working board.

There is no substitute - that chip that is too hot to touch needs to come OFF to at least take That the short away then it's possible there are other faults if its liquid damaged ,the board will still function if the chip is removed except no HDMI.

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