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Helpful answers
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Dec 31, 2015 5:28 PM in response to RustyQShacklefordby Malcolm J. Rayfield,Try it with the ceter pin disconnected. There are reports of this fixing 23" display power supplies. It may not help the 30", but shouldn't cause any damage.
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Dec 31, 2015 6:08 PM in response to Malcolm J. Rayfieldby RustyQShackleford,Thank you for the speedy reply. The problem is, I grabbed the tiny PCB (from an old 23"-size PS brick) that holds the connector socket plus a 1K resistor and maybe some other stuff. There seems to be 4 Kohms (measured) between the connector center pins and one side of that 1K resistor (and the other side of the resistor is connected to GND). IOW, I can't just disconnect the center pin (without hacking into the cable, which I HATE to do). I thought about disconnecting the 1K resistor, to see if that'd work. Or maybe trying the hack where you somehow slip a piece of paper into the connector so the center pin can't make contact. I'm guessing that either the 1K resistor, or the mysterious 4K resistance between the center pin and the 1K resistor, is used to indicate (to the monitor) which size PS it is (90w or 150w), and I need to somehow defeat that scheme - just not sure how.
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Dec 31, 2015 6:44 PM in response to RustyQShacklefordby RustyQShackleford,I did the "Jakobean" trick, i.e. sticking a tiny piece of paper in the connector so that the center pin can't make contact, and it works !
I now just have to see if I can duplicate this by somehow hacking the little PCB (from a dead brick) - to avoid having to cut into the cable from the monitor or using the little slip of paper.
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Jan 1, 2016 2:35 PM in response to RustyQShacklefordby RustyQShackleford,Apparently the power supply signals to the monitor, via that center pin, whether it's the 65, 90, or 150 watt version. How ? I guessing it pulls down on that wire (the 5Kohm resistance to GND I'm measuring) a certain amount. The lower-wattage PS pulls down harder, and tells the monitor it's not powerful enough (so the monitor pilot light gives the error code). The more powerful PS pulls down less (or maybe not at all ?) which explains why simply cutting that wire in the cable (or using the piece of paper to block contact) allows the monitor to work properly (assuming, of course, that whatever PS provides enough 24vdc power).
I've read elsewhere that the center pin provides 5vdc for the USB ports on the monitor, but I'm not sure I believe that.
It would be nice if this were all documented, somehow - but I guess that's not Apple's style ...
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Sep 19, 2016 5:41 PM in response to RustyQShacklefordby davizmr,Hi,
Did you managed to make it work?
I am looking for an used 150W one but they are all above 140 USD. Crazy.
Thanks in advance!