I'm at a loss

It's not a frequent thing when I'm at a loss on how to fix something, especially with anything electrical.

It's usually a cold day when I give up on something, and I'm usually the last to give up, and I usually give up for good reason. I only had one false-positive, in relation to a bad device, ever. I rid myself of a Linksys LNE100TX, which is a very good NIC, for a D-Link DFE-430TX, also a good NIC, and when I returned back and installed the D-Link, I found the source of my problem, which persisted through NIC changes, however I had garbage-d the Linksys already and was unable to retrieve it.

I've done crazy things with computers, from building something from scratch, to fixing the otherwise unfix-able, that others have given up on as "too frustrating", all the way to re-soldering resistors onto the power-riser on a laptop that wouldn't power-up (it worked afterward by the way).

My point here is, I'm usually the last to give up, and if I give up, I have a good reason. My expertise with all these things is fairly expansive, and only hits a limit when dealing with determining problems on a circuit-by-circuit basis. I have a multimeter, but I'm not always sure what information it's giving me, or how relevant it is.

I recently have been working on a friends Dell XPS m1330, which has a bad video processor (on-board on motherboard), requiring a motherboard replacement. I ordered one, it happened to be from China. The shipping time and method was reasonable, when receiving it, the packing was adequate and the board looks to be in good condition. Upon installing the board, and applying all the screws, cases, cards, thermal paste and coolers (including modifications to the original design, ergo: "copper mod"), I attempted to connect power before I powered up the unit, to test for function, and the charging light didn't come on... that's odd.

I checked, and found the power-light on the PSU wasn't lit. okay? it's plugged in, what gives?

after extensive testing, the new motherboard seems to be causing the power supply to randomly turn off. Probably a fault safety or something. I connected the system to another PSU (variable Voltage, adjustable, universal laptop power supply), and all that accomplished was to reduce the (albeit small) display on the cord, which normally shows the voltage, to a very dim jumble of non-sense data. Removing from the system, the display reset to it's lowest value, 15V, attempting a 15V connection, resulting in the same problem.

Attach either of these power supplies to the original mainboard, that works apart from the graphics being completely unusable, and the result is the same: it works.

I emailed the supplier who claims "it was tested before being sent out"... if that's the case, then sometime between you testing it, and me testing it, it stopped working.

I've handled the motherboard actually BETTER than the original one that came with the system (which I accidentally dropped on the floor from about a foot up), and the original works, the "new" board doesn't. explain that.

The supplier is willing to do an exchange, so the board will be going out on Monday.

I can't help but be a tad bit insulted by the insinuation from the supplier that I'm wrong, and the mobo works. I tested the thing, I even checked the resistance of the original mainboard's pos and neg terminals (incoming to the system), and the resistance between them is very similar (there will be variance between the two due to a tolerance in the resistance of every resistor on the board, eg. 100ohm resistor with +/- 5% tolerance could be anywhere from 95 to 105 ohms in resistance). So, in theory, they should both be very similar. I even tested it with the elbow for the universal power adapter plugged in to check for faults in the power adapter, which I would've been willing to desolder and exchange with the power connector from the original mobo, if I thought it would fix the problem, however, the resistance doesn't change, indicating no short in the connector.

I'm baffled. Apart from a major fault of a circuit that handles the current on the mainboard, that isn't obvious, I don't see why this would be happening.

Oh well, another 2-3 weeks before I can reassemble this with yet another motherboard.