Fried computer - why??

[EWCguy]

Although it may not isolate the problem that destroyed the laptop, having identified a difference in hum on the system with this one aisle light circuit turned on/off surely tells us something. I'm imagining that when the contractor tapped into the electrical panel (or when they were finished), it resulted in dislodging a ground or neutral for this circuit. Could both the augmented hum (as picked up by the antenna supposition) and the electrical ground fault be caused by this one problem? My idea here is that once the computer fried, the AC ground problem was then "open" again and the remaining audio connection to the computer became the antenna.

Once the electrician opens the panel, it may be obvious to them regarding the status of connections there. I should look again at the panel to see if any labeld circuits match the outlet on the stage... having those two in proximity would certainly allow for crossed wires.

In testing with my assistant the other day with audio on and connected (mic cable only), we did NOT discover voltage potential between the outlet used to power the computer and the audio system on any mic pin with AC circuit neutral or ground (we also ruled out the AV cart power strip, another variable that was involved). There was an expected ~120v AC potential between the AC load side and each of the mic jack pins. ** The same was true when tested again with all aisle light circuits on. **

 

[TimMc]

Fried computers are better than steamed, broiled or baked, and don't even think about boiling... They never even get to al dente.

Thanks for the clap, folks! I'll be here all week!

 

[JD]

Still, Laptop should not have been at ANY potential. If there was nothing else connected to it that could leak voltage, then it leads back to the AC adapter / supply. The frame of the laptop (Jack shells) should be open circuit with reference to ground. However, to test this, do not use the "ohms" setting as you may fry the meter. Plug in the supply, set the meter to AC 200 volts (or close) and measure from the metal shell (barrel) of the DC connector to ground. Treat the DC connector as a live wire until the meter proves it isn't. If you are seeing a significant voltage, have the laptop supply checked out professionally.

 

[Ben Stiegler]

Uh, is there any step down transformer on the aisle lights, or are the lamps 120? If xfmr, check it out for short between primary/secondary, funky ground, etc

 

[EWCguy]

Update from physical plant:

>> Found a missing ground wire on the apron receptacles, pulled new grounding wire for apron receptacles. << Laptop was connected where they *found* ground, projector was connected where ground was *missing*
>> Found and repaired poor neutral connection for the aisle lights.

I'm still not sure how this ties the two systems from two different circuit-breaker panels in different rooms together. I'll do the previous "antenna" test to see what happens. If no increase in ground hum, then it's time to try JD's test before we toast another laptop.

Still, Laptop should not have been at ANY potential. If there was nothing else connected to it that could leak voltage, then it leads back to the AC adapter / supply. The frame of the laptop (Jack shells) should be open circuit with reference to ground. However, to test this, do not use the "ohms" setting as you may fry the meter. Plug in the supply, set the meter to AC 200 volts (or close) and measure from the metal shell (barrel) of the DC connector to ground. Treat the DC connector as a live wire until the meter proves it isn't. If you are seeing a significant voltage, have the laptop supply checked out professionally.