Understanding Computers/AC adapter for HP Compaq nx7300


DJ SIMBA wrote at 2008-08-04 15:50:13
Hi, i seem to have a similar situation with my HP compaq nx6310 AC adapter. It has the same 7.4mm cylinder power jack with the small centre pin inside that provides 2 voltage outputs.

 The laptop will run perfectly fine on battery power but when you insert the AC power cable it slows down hugely. almost unusable.

 When measured with a voltmeter, between the outer cylinder and the inner cylinder of the plug, i get 18.6v. But when measured from outer cylinder to the centre pin i only get 12.5v.  After searching numerous forums for days and finding nothing, i brought myself to the conclusion that the AC adaptor must be faulty.

 It is a cheap replacement adapter made in china.  Il have to invest in a genuine HP adapter and see if there is a difference.

Ken wrote at 2010-07-12 08:44:58
Hi all.

I also am interested in this discussion.  I acquired an HP notebook (G61) recently when my previous notebook died, and was most disconcerted to discover the centre pin.  I only went so far as to measure the output voltages present open-circuit, but my experience as an electronics engineer lead me to suspect it was some kind of feedback arrangement.

The reason for my research is a desire to re-use my universal car power adapter, which of course only has the one fixed output (selectable voltage).  I have a suitable connector, but no means to provide the electrical requirements it seems (in the absence of proper data from HP).

My conclusion: unless I can locate more data, I shall give up and resort to my car-to-mains adapter to feed my notebook mains-to-DC adapter (inelegant, but it will do the job).  Next time I'm shopping for a notebook I shall look more carefully at the PSU requirements, as I am now effectively "locked in" to HP spares if my PSU goes down (maybe I need to think of getting a spare just in case - I would only have 2 hours of computer use left if it did, and then only if I noticed that the battery wasn't charging).


Jardaj wrote at 2012-07-12 14:07:21
It is much easier - it is a system by which laptop you "check" source of originality. The source is the PIN and the positive lead connected resistor 270kOhm. The original source and the connector is 3 wire.

In non-original sources, or reduce the resistance involved directly inside the connector. The sources go in this case only two wires.

Notebook check its value to control the PIN and then "allows" charging.

Dell uses the same system, except that a different resistance value. Therefore, the source from Dell, though it has the same connector does not work.

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Understanding Computers

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David Freitag


I can answer questions about all kinds of computers, operating systems, software and hardware in clear and easily understandable language. I have dealt with sorts of software and hardware issues in PCs from before windows to the present. I can explain basic concepts and deal with complex detailed issues in the guts of operating systems, including drivers, bios, hardware issues and software problems.


I have over 3 decades of experience ranging from mainframes and minis and microcomputers to all flavors of personal computers. I have programmed in assembler language, Fortran, C, VB, C# and I have worked with the major relational databases. I have been a CIO of an energy company and I have provided hands on technical management for Windows software development. In the course of my career, I have had to deal with all sorts of configurations and nitty gritty system problems which exposed me to all aspects of personal computer systems.

I am an expert author in Ezinearticles and have had articles published in Buzzle, IdeaMarketer, ArticleCube and other article sites.

I have a BS in Physics from CCNY. I have received credits from courses dealing with OLE automation and computer systems management from the AMA

Awards and Honors
Phi Beta Kappa Achievement awards for software development efforts in a leading Voip provider company.

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