What is the "signal" pin on the power supply cable for?

X60/X61 series specific matters only.
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What is the "signal" pin on the power supply cable for?

#1 Post by rakirkp » Sun Nov 21, 2010 3:28 pm

What is the "signal" pin on the power supply ("AC Adapter") cable for? I would like to power the PC from a linear power supply to reduce RFI.

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Re: What is the "signal" pin on the power supply cable for?

#2 Post by rkawakami » Sun Nov 21, 2010 6:56 pm

Welcome to thinkpads.com!

My best guess is that it's used to identify the type of power supply (65W vs 90W) that's connected to the system. Given the adapter that's described in this thread: http://forum.thinkpads.com/viewtopic.php?f=18&t=91992 , not connecting anything to that center pin might mean that the laptop will assume that the 65W supply is being used. I say that since to me that's the logical choice; you wouldn't want the system to think it's using a 90W supply and configure itself to use more power than what's available from the adapter.

My X60 systems report correctly that a 65W supply is connected (under the Battery tab of the ThinkVantage Power Manager). I don't seem to have a 90W supply around here but I'd imagine that if one were used, the Power Manager would "see" it. I've measured the center pin with respect to ground; the metal on the outside of the DC plug. There's no voltage present when the supply is plugged in but there is a resistance of 10Kohms when it's unplugged. Maybe if somebody has a 90W supply they can measure the resistance and report.
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