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Magsafe Mystery

G

grantza

macrumors newbie
Original poster
Jun 9, 2014
13
0
Cape Town
I lent an old MBP (15") to a friend. (MBP 3.1)
Somehow, she managed to damage / destroy the Magsafe adaptor.

I realized I had a cable with a Magsafe adapter still on it from an old 13" MacBook (the power unit packed up - so i nipped the cable off it before chucking it out).

I replace the now crushed MagSafe adaptor with the "good" adaptor from the old 13" MacBook's power supply (so now the old MagSafe adapter from the 13" MB is connected to the 85w power supply for the 15" MBP)

Green LED comes on - but no power.
Remove battery & power - do SMC reset - still just green LED & no power.

Remove battery & power, SMC reset again, but this time keep holding the power button down as I connect the MagSafe adapter - continue to hold for a further 5 secs, release power button, & press power button again.
Machine starts up.

However, the fans are flying at full speed & keyboard backlight does not work.
Shutdown, restart & do PRAM reset (3 loops).
Machine restarts - fans still at full speed. (all other functions are perfect).

Is there an incompatibility issue with the MagSafe adapter that came with the power supply units (60w or something) & the MBP's 85w power supply.
I do know the centre pin on the MagSafe adaptor carries certain info between the power supply unit & the machine itself.

***Note***
A friend has the same spec machine as the one in question here, manufactured about 3 months apart.
My power supply (with the newly attached magsafe adapter) starts his MBP perfectly.
His power supply starts my MBP perfectly (as it usually should).
This to me, seems to eliminate a problem on the logic board

Any ideas ?
 
The MagSafe connector includes a chip, that stores some information about the charger (power rating, ID, revision, family, serial number, etc.), and after reading this information the SMC negotiates a connection with the charger. The problem could be, that the old MBP does not recognize the charger with its newer family number as a genuine charger, while a slightly newer MBP recognizes it.

There's an Apple support article about some compatibility issues with 2007-2008 MacBook Pro's, see http://support.apple.com/kb/TS3499

If this is what's going on in your case, there's a firmware update available that could possibly fix the issue. But you might need OS X 10.5 or 10.6 to install it: http://support.apple.com/kb/DL1312
 
laurihoefs said:
The MagSafe connector includes a chip, that stores some information about the charger (power rating, ID, revision, family, serial number, etc.), and after reading this information the SMC negotiates a connection with the charger. The problem could be, that the old MBP does not recognize the charger with its newer family number as a genuine charger, while a slightly newer MBP recognizes it.

There's an Apple support article about some compatibility issues with 2007-2008 MacBook Pro's, see http://support.apple.com/kb/TS3499

If this is what's going on in your case, there's a firmware update available that could possibly fix the issue. But you might need OS X 10.5 or 10.6 to install it: http://support.apple.com/kb/DL1312
Click to expand...

Appears the MBP already has the latest firmware available (SMC Version (system): 1.16f11)
 
grantza said:
states:
Alert
This computer does not need this update
Click to expand...

Is any adapter info visible in System Information > Power > AC Chargers when it's plugged in? What does it say?

Also check that your battery condition is 'Normal'.
 
The "intelligence" of the MagSafe adapter is in the plug. So, basically, you have an 85 watt adapter which identifies itself as a 65 watt adapter.

Could it be that the MBP is ignoring the adapter because it thinks it's too small? It definately won't run and charge the battery simultaneously in that configuration.
 
jruschme said:
The "intelligence" of the MagSafe adapter is in the plug. So, basically, you have an 85 watt adapter which identifies itself as a 65 watt adapter.

Could it be that the MBP is ignoring the adapter because it thinks it's too small? It definately won't run and charge the battery simultaneously in that configuration.
Click to expand...


this is what i also initially thought, however, it powers up & charges a friend's identical model / spec MBP
 
grantza said:
I lent an old MBP (15") to a friend. (MBP 3.1)
Somehow, she managed to damage / destroy the Magsafe adaptor.

I realized I had a cable with a Magsafe adapter still on it from an old 13" MacBook (the power unit packed up - so i nipped the cable off it before chucking it out).

I replace the now crushed MagSafe adaptor with the "good" adaptor from the old 13" MacBook's power supply (so now the old MagSafe adapter from the 13" MB is connected to the 85w power supply for the 15" MBP)

Green LED comes on - but no power.
Remove battery & power - do SMC reset - still just green LED & no power.

Remove battery & power, SMC reset again, but this time keep holding the power button down as I connect the MagSafe adapter - continue to hold for a further 5 secs, release power button, & press power button again.
Machine starts up.

However, the fans are flying at full speed & keyboard backlight does not work.
Shutdown, restart & do PRAM reset (3 loops).
Machine restarts - fans still at full speed. (all other functions are perfect).

Is there an incompatibility issue with the MagSafe adapter that came with the power supply units (60w or something) & the MBP's 85w power supply.
I do know the centre pin on the MagSafe adaptor carries certain info between the power supply unit & the machine itself.

***Note***
A friend has the same spec machine as the one in question here, manufactured about 3 months apart.
My power supply (with the newly attached magsafe adapter) starts his MBP perfectly.
His power supply starts my MBP perfectly (as it usually should).
This to me, seems to eliminate a problem on the logic board

Any ideas ?
Click to expand...

The 13" models use the 60 watt adapter. Since the internal chip is in the head of the MagSafe itself, and not in the brick you essentially put a Chihuahua's head on a Great Dane.

Since the other adapter works fine, I recommend buying a new adapter. You may be able to get lightly used adapters from eBay or shopgoodwill.com.
 
grantza said:
***Note***
A friend has the same spec machine as the one in question here, manufactured about 3 months apart.
My power supply (with the newly attached magsafe adapter) starts his MBP perfectly.
His power supply starts my MBP perfectly (as it usually should).

Any ideas ?
Click to expand...


Yes. Trade power adapters.
 
JustinePaula said:
"put a Chihuahua's head on a Great Dane."

The mental picture....thanks for the laugh...OMG
Click to expand...

Your welcome. I laughed thinking of how to write it.

grantza said:
I chuckled as well.
Had a vision of a scene in the movie Mars Attacks.
Click to expand...

You can get a gently used or new MagSafe on eBay or Amazon for not much dough in comparison to using your "mutt" charger. I'd recommend doing that.
 
Altemose said:
Your welcome. I laughed thinking of how to write it.



You can get a gently used or new MagSafe on eBay or Amazon for not much dough in comparison to using your "mutt" charger. I'd recommend doing that.
Click to expand...

It's for an old spare MBP, so I am in no rush - was more curious as to what was going on with the MagSafe adaptors.
I'll be in London for a few days next week, will pick one up there.

Here in South Africa you get screwed over so badly by the Apple distributor - they do not even bother to offer a dab of KY to ease the pain !
 
I'm still quite intrigued by this, and have been thinking what could explain this behaviour.

All the logic is in the connector. So it should not matter what's at the other end of the power cord, as long as it supplies the correct voltage. But that's the one key difference between the 85W and 60 W chargers: the 85 W charger provides 18,5 V, while the 60 W one provides 16,5 V. So maybe this is about component tolerances.

If the SMC detects the charger as a 60 W version, it's going to expect a voltage close to 16,5 V. Your power supply should provide 18,5 V, but due to component tolerances, the real output may be a bit lower or higher, and might fluctuate. So maybe it just happens, that your charger is on the high side.

Then there's the power-in board, which has voltage and current sensing circuitry. Maybe it also happens to detect the voltage as slightly higher than it actually is. Combine this with the higher-than-expected voltage, and the power-in board might detect it as a fault, and prevent charging.

If the other computer happens to have components from the other end of the tolerance scale, it might not detect the over-voltage, and allow charging, despite the voltage being on the high side.

Well, maybe someone can come up with a better explanation, that's all I can come up with :D
 
laurihoefs said:
I'm still quite intrigued by this, and have been thinking what could explain this behaviour.

All the logic is in the connector. So it should not matter what's at the other end of the power cord, as long as it supplies the correct voltage. But that's the one key difference between the 85W and 60 W chargers: the 85 W charger provides 18,5 V, while the 60 W one provides 16,5 V. So maybe this is about component tolerances.

If the SMC detects the charger as a 60 W version, it's going to expect a voltage close to 16,5 V. Your power supply should provide 18,5 V, but due to component tolerances, the real output may be a bit lower or higher, and might fluctuate. So maybe it just happens, that your charger is on the high side.

Then there's the power-in board, which has voltage and current sensing circuitry. Maybe it also happens to detect the voltage as slightly higher than it actually is. Combine this with the higher-than-expected voltage, and the power-in board might detect it as a fault, and prevent charging.

If the other computer happens to have components from the other end of the tolerance scale, it might not detect the over-voltage, and allow charging, despite the voltage being on the high side.

Well, maybe someone can come up with a better explanation, that's all I can come up with :D
Click to expand...

I am not aware of the differences but your answer definitely makes sense! In simple terms, the OP has to get rid of the mutt of a charger.
 
laurihoefs said:
I'm still quite intrigued by this, and have been thinking what could explain this behaviour.


If the other computer happens to have components from the other end of the tolerance scale, it might not detect the over-voltage, and allow charging, despite the voltage being on the high side.

Well, maybe someone can come up with a better explanation, that's all I can come up with :D
Click to expand...

I too am intrigued.
The other MBP that the charger / MagSafe works on has a manufacture date 3 months apart (earlier).
There are 2 other small differences:
My MBP has 4GB RAM - the other has the standard 2GB.
My MBP has a 320GB 7200rpm HD - the other has the standard 160GB @ 5400rpm.
Otherwise identical.
 
grantza said:
I too am intrigued.
The other MBP that the charger / MagSafe works on has a manufacture date 3 months apart (earlier).
There are 2 other small differences:
My MBP has 4GB RAM - the other has the standard 2GB.
My MBP has a 320GB 7200rpm HD - the other has the standard 160GB @ 5400rpm.
Otherwise identical.
Click to expand...

I would just get a new MagSafe adapter to be honest with you.
 
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