[Cube] smoking Cube

[Dan Oetting]

On Jan 28, 2007, at 10:51 PM, Jan Georgen wrote:

> Good  evening. The saga continues. I was ready to start random  
> swaps (since I happen to be a random-styled thinker) but heeded  
> Dan's advice. For the most part. I pulled the hard drive then  
> plugged in the power supply, then observed. Quickly.
>
> The red light/lcd turned on when the power was plugged in (no power  
> switch attached).
> Very shortly thereafter, there was a popping/crackling sound.  
> Followed by smoke emitting from both sides of video card. Followed  
> by a pungent, metallic odor.
> Then a quick pull-out of the power plug.
>
> then a quasi-systematic take-apart, down to the pulling out of the  
> DC-DC board. The gold contacts on the DC board that fit into the  
> slot on the motherboard (the slot you have to push the 'ejector' to  
> release the DC board) have a sort of gold-ish crust around each  
> point and another sniff test yields sharp remnants of that metallic  
> odor. Sort of smells like fingernails on a chalkboard sound, if you  
> can switch sensory brain parts.
>
> That's where I stopped tonight. Thoughts?
>
> Thanks so much for all the ideas, directions, and warnings.

The golden crust might be normal, this could be a resin used in  
soldering or an insulator applied over high power circuits. I'm  
suspecting you have a damaged IC that is shorting out a power supply.  
The IC could be cracked open and there may be a whitish spray of what  
used to be the thousands of transistors in that IC. The power leads  
going to that IC should show clear signs of overheating from  
blistering of the protective coating on top to darkening and burning  
of the epoxy/fiberglas circuit board.

When one IC melts down like this, any of it's inputs and outputs  
could connect to higher voltages supplied to the chip and propagate  
damage to other chips. The short circuit will invariably propagate  
damage back towards the power source, blistering circuit traces,  
melting wires, tarnishing contacts and burning out the power supply.  
This cascading effect is why it's usually a bad idea to randomly swap  
components when there is a serious failure. You could easily end up  
with two dead machines. [Most failures are minor involving broken  
bonding wires inside ICs, failed open gates, cracked traces on  
circuit cards or low current shorts. These failures don't make smoke  
and usually don't propagate failures to other parts of the system.  
Swapping parts is then usually a fast technique to locate the problem.]

What you need to do is visually inspect the boards to find the  
damage. Then follow the power lines back to see if this caused any  
permanent damage to another board. The most serious problems would be  
if insulation on wires melted through to cause other short circuits  
or if a DC-DC converter failed and delivered a high voltage to a low  
voltage circuit. The spray from the failed IC can also contaminate  
other boards. After the visual inspection, sometimes you can simply  
remove the failed board and smoke test the rest of the system. Check  
the voltages on any power circuit feeding the removed board. If you  
can get schematics or a diagnostics/repair manual, they usually list  
the voltage test points. Otherwise you can make comparisons with a  
working system.

-- Dan Oetting