MagSafe mystery

Grant

Grant

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I lent an old MBP (15") to a friend.
Somehow, she managed to damage / destroy the Magsafe adaptor.

I realized I had a cable with an 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.
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.

Any ideas ?
 
There ought to be no problem, there are only x2 wires in the lead itself....I have extended one of mine with x2 core ripcord.
I ran my 2010 13" MBP on 60w and 85w chargers, all pre latest magsafe adapter, and now using them with the add-on adapter on my 2013 13" MBPR no issues.
Just check if the charger points are clean...unplug the charger, wait a few min then with some Q20 or similar and a toothbrush, clean them and check they move in and out freely..the little brass contact pins, then switch off laptop and do the same to the charge port,....also see if any small pieces of metal have possibly gotten into the adapters or the laptop charge port...use magnifying glass if need be, and remove with tweezers.
PM me if you wish.
 
Last edited:
D tj said:
There ought to be no problem, there are only x2 wires in the lead itself....I have extended one of mine with x2 core ripcord.
I ran my 2010 13" MBP on 60w and 85w chargers, all pre latest magsafe adapter, and now using them with the add-on adapter on my 2013 13" MBPR no issues.
Just check if the charger points are clean...unplug the charger, wait a few min then with some Q20 or similar and a toothbrush, clean them and check they move in and out freely..the little brass contact pins, then switch off laptop and do the same to the charge port,....also see if any small pieces of metal have possibly gotten into the adapters or the laptop charge port...use magnifying glass if need be, and remove with tweezers.
PM me if you wish.
Click to expand...

everything was clean, but gave the magsafe adaptor & the connector area on the laptop a good cleaning for good measure.
pins all move freely & smoothly.
power supply itself is good, when magsafe is not connected to laptop, the power supply delivers the correct 6v (forgot the exact voltage), when connected to the mbp and one hits the power button, the laptop sends the correct signal & the power supply responds & delivers the full voltage (18v.)

i did however notice a very distinct difference in the core of the cable between the 65w & 85w power supply units - the 85w cable core is considerably thicker / heavier - this is immediately noticeable.


the other thing is the startup of the mbp itself.
with the magsafe adapter from the 65w power supply, the machine will not start unless the power button is being held down (and held for a further 5 secs or so) while the magsafe adapter is being connected to the laptop.
failing the above procedure, the mbp simply will not start up.


**
i found another magsafe adapter from another older 15" mbp.
removed the adapter that came from the 13" machine & replaced it with the one from the 15" machine I had just found - works perfectly.

odd !!
 
Thanks for the Magsafe teardown link, very interesting, my guess is 15" MB does not "like" the 13" magsafe cable even if on the correct charger....85W .
I have only used 13" MBooks on my chargers, so not had this issue.
If that 13" lead is going begging, I'm interested: I want to split a lead to be able to charge from either side of my bed.
 
so, i got curious about this again.
seems the SMC version on the laptop & the magsafe plug (centre pin) do a bit of chatting.

when the magsafe plug is connected, it communicates with the SMC.
SMC will decide whether the power supply is good enough or not.
the chip inside the magsafe plug, identifies itself as either from a 85w (15") or 65w (13") power supply.
if SMC is happy with what it sees, it then tells the power supply to release it's full voltage.

however, SMC versions seem to come into play as well.
so the SMC version on the machine in question is specifically looking for a magsafe plug identifying itself as 85w - which in this instance, is not the case - it is identifying itself as 65w & therefore the SMC is not issuing a command for full voltage

this article explains a little more - although it related to a 13" mbp, the symptoms are similar & make sense.
http://forums.macrumors.com/showthread.php?t=1122338
 
grantza said:
the chip inside the magsafe plug, identifies itself as either from a 85w (15") or 65w (13") power supply.
if SMC is happy with what it sees, it then tells the power supply to release it's full voltage.
Click to expand...

60W, not 65. There are three bricks as far as I know: 85w (15/17"), 60w (13") and 45w(Air).
 
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