Power Failure/Short Circuit

Hello Jamie,

I recently had the same power problem with my M1730.  The fact that the power brick light comes on when you disconnect from the computer and cycle the power at the wall socket, but then goes out when you plug it into the computer indicates a short circuit somewhere in the computer.

The most likely place is the power supply, but on these notebook computers, that's integrated into the motherboard, so the first thing to try is replacing the mobo.  In my case, that didn't solve the problem - the short turned out to be in the video card (8800M GTX SLI).  Obviously, replacing two major subsystems is very expensive, unless you're covered by a warranty or service contract, as I was.

If you're not under warranty, and feel comfortable disassembling a notebook computer (much harder than working on a desktop, BTW), you can try downloading the service manual.  You can't really diagnose a mobo problem without test equipment, but if the short is not in the mobo itself, you can narrow the problem down by unplugging the major subsystems one at a time, then testing with your power brick.  In my case, removing the video card, unplugging the power brick from the computer, cycling the power at the wall socket so that the power brick's light comes on, then plugging the brick back into the computer would have resulted in the light NOT going out.  (No need to actually boot the computer for this test.)  So one could conclude the video card was the culprit.  If the short is in the mobo itself, though, every test would fail (i.e., power brick's light would go out every time).

As for swapping out CPUs and screens on a replacement system you got off Ebay, it might work, but no guarantees.  It's possible that Dell has upgraded to a new mobo for your machine which supports a faster CPU than that of the Ebay machine.  You'd have to check parts lists on both machines to see if they're the same.  The WLED screen is more likely to be swappable than the CPU, but its possible that it has different power requirements (voltage, in particular).  Again, you'd want to see if both machines are using the same mobo, as the screen gets its power from there.

Of course, any major surgery of this sort on your notebook will probably void your warranty, so if you're still covered, it's best to let Dell do the servicing.

Best,
BT

Thanks. I have already taken the machine apart and have tried disconnecting everything I could and the power brick LED still went out. I think the M1730 must be different to the M1330 as I am pretty sure I saw the nVidia chip soldered to the main board so I don't think I can check/replace that. I'm not sure where I can find out if the chip/screen is compatable, I was hoping someone on here might know or be able to point me in the right direction.

Thanks very much for your reply, Jamie

Hi Jamie,

Thanks for the additional information.  I assume you're no longer under warranty.

I took a look at the service manual for the M1330, and the customizable options if you were to purchase one from Dell today.  Here's what I would conclude from that:

There's nothing about being able to remove the video card in the service manual, and there's only one option available for purchase, (8400M GS), so I concur with your observation that it's wave soldered onto the mobo.  Since you've done the unplug-the-subsystems test, it looks like you're going to need a new motherboard.  (Unless you have access to test equipment and can track down the short on the mobo yourself.)

I also checked the CPU options, and I'm guessing that you have a T6400 processor.  Checking on http://processorfinder.intel.com/Default.aspx I find that this CPU uses an 800MHz front side bus (FSB), and the feature size of its die is 45nm.  I'm guessing the machine you're looking at on Ebay has either an L7400 or T5250 processor, most probably the latter, and these have a 667MHz FSB and 65nm feature size.  So there's got to be different mobo's used in the two machines, and different Northbridges.  (The 45nm parts use lower voltages than the 65nm, for example.)  So I'm guessing your plan to swap CPUs and screens won't work.

If, however, the processor in your current machine is a T5750 or a T7200, there's a much better chance your plan would work.  Both of those have a 667MHz FSB and 65nm feature size.

My advice would be to see if you can purchase a reconditioned mobo from Dell (or whoever Dell gets its parts from) which supports your particular CPU, and do the replacement yourself.  That may even turn out to be cheaper than your Ebay plan.

Best of luck,
BT

Hi,

I don't know much about the ebay machine, I've asked for the service tag, hopefully I might get it before the auction ends :)

The processor in my machine is a T7250 I think, they have a 800MHz FSB, but I notice there are 1.8GHz processors with 800MHz FBS so there's not much point speculating :-/

Thanks again, Jamie

This guy reckons that the screens are compatibile.

http://forum.notebookreview.com/showthread.php?t=258686#post3462953

Well, the T7250 is a 65nm device, rather than the 45nm CPU's Dell offering in new M1330's, so that's a good sign for your Ebay plan.  I've seen designs in which the CPU's FSB doesn't match the maximum supported by the mobo, though it's obviously suboptimal.  So it's possible the same mobo is being used in both cases.  (The feature size is a better determinant than the FSB.)  And if the same mobo is used, it's likely your WLED screen will work, too.  The other post you pointed to is a good sign as well.

FWIW, Dell offers a refurb mobo for the M1330 for about US $410: 

Another thing to keep in mind is that Nvidia admitted to a design flaw with its 8400 series chips, and Dell has some program to address this problem.  I don't know the details, as it doesn't apply to my M1730, but if your video chip is the source of the short, there might be some way you can get it repaired for free.  A quick search brought up this post:  http://en.community.dell.com/forums/t/19223085.aspx?c=us&l=en&cs=19&s=dhs

Hope that helps.

Best,
BT

I guess so:

http://en.community.dell.com/forums/t/19251593.aspx#19467254

Very common issue. The motherboard can be repaired...although not sure if it's less than what you're going to find a donor M1330 for, ....but AQSTECH.com does these repairs for $100