Newsgroups: sci.electronics.misc
Subject: Re: A S-Video connection fried both my laptop and TV! Help needed!
References: <[email protected]>
"Gabriel"  writes:

> Hello,
> 
> Recently, I had a big power surge problem involving both my brand new
> laptop and my less than two years old TV. Two total looses.
> 
> My main concern is that I don't really understand what happened and,
> thereof, can't see a way to prevent it in the future.

I just can give quesses also... 
To giv definitive answer, I would need to be in place with 
some measurement instruments... 

 
> Here's the story :
> 
> I bought a few weeks ago an HP notebook with an S-Video output. I used
> my laptop (on battery and AC power) a week and a half before trying the
> S-Video output and did not have a single problem.
> 
> So, someday, I decided it was time to try to connect my laptop on my TV
> by using the S-Video output. I bought a S-Video-to-RCA cable at
> Radioshack because I thought it would be more practical to have my
> laptop connected to the front RCA jacks of my TV.

Generally sounds OK. 
The safest idea is to do the connection while the components 
are turned off and not plugged to wall... 
Sfest bet in connection is to make sure your PC is 
not connected to mains, connect the video cable and then 
plug it to wall if needed...

> As soon as the contact was made, both my laptop and TV went off and I
> could smell a light odour of burnt electronic components. The TV did
> not seem to be damaged because I could turn it on almost immediately.
> As for the laptop, I simply had to reinsert the battery to make it
> start.

Sounds like you got quite a surge to the system.... 

> Maybe it was very stupid, but I thought that the problem could be the
> cheap RadioShack cable. So I decided to buy a true S-Video cable.

Most propably the problem here was not in the cable construction itself.. 

> For my second try, I choose to not plug the laptop into the AC outlet
> and just use the battery. After connecting the laptop to the TV, all I
> see is a black screen. By the way, I did not feel like there was a
> power surge problem this time.

The surge could have damaged the video output on your PC or 
the input on the TV.. A surge through RCA connector can 
cause this.. RCA connector is a very stupid connector 
for audio/video connection because normally it connectes the 
center pin that carries the signal before the signal ground, 
allowing the potential difference between the different equipment 
to enter the equipment as surge! This has damaged many equipment 
in systems where there are ungrounded PCs or other grounding problems... 
I know people who have damaged for example PC sound cards, PC video 
cards, TV audio/video inputs, AV amplifier audio/video connections etc.. 
And the real life experiences (few damaged components) have teched 
me to become careful.

In the computer connections there would be lots of less 
damaged equipment if proper connections for the applications 
are used... Professional audio/video world prefers 
XLR and BNC connectors for their connections, both of those 
guarantee that ground gets always connected first... 
Lots of less fried equipment and more reliable connections. 


If things are correct, meaning the cable is correct and still working, computer 
settings are correct, TV video input still working and TV settings correct 
you should get picture when you run the computer from battery. 
Generally with a laptop it is safest to run the computer from 
battery on its own (not connected to anything else connected 
to mains power or anything else). When you have just the computer 
running with batteries it is harver to fry it...

> Days later, I really wanted to make my S-Video port work. So, I
> downloaded the latest devices drivers for my graphic card and gave the
> S-Video output a new try with the laptop connected to the AC outlet.
> Not a good idea.
> Again, as soon as the contact was made, both my laptop and TV went off
> and I could smell a strong odour of burnt electronic components. This
> time the damage was terrible. Both my laptop and TV are completely
> fried. There is just no way to make'em work anymore.

I would have tried the computer running at batteries without mains 
connection. Your sirge problems are most proplably somehow related 
to AC power connection. 
 
> So my questions are :
> 
> 1) What happened ?

There was some form of surge formed when you do the connection. 
There are varuous possibilities. Some possibilities:
- your TV is conencted to cable TV system that is not properly 
  grounded and there is some energu there that gets through 
  your cable and equipment to mains ground
- your ungrounded TV + DVD system is not connected to cable TV outlet, 
  but some equipment inside it is damaged to that the mains power 
  gets to the equipment case + AV conenctor ground, when you 
  do connection to grounded PC you will create a short circuit 
  (this will generate huge surge and generally burn fuse on mains panel), 
- Your TV system is connected to properly grounded cable TV connection 
  (or properly grounded antenna on your roof) but the is something 
  wrong in the grounding of your mains outlet grounding (miswired etc..) 
  so you mains outlet ground has some power on it, when you equipment 
  chain makes link to cable TV ground you get a large current surge 
  through your wiring and equipment (might not burn any fuses..)
- your TV + DVD system is not connected to cable TV or other ground, 
  the ungrounded properly working equipment "leak" some small amount 
  of power to their cases (this is normal), so the cases are 
  not at ground potential (usually at around 30-60V AC potential 
  if you measure them agains ground with a modern multimeter), 
  when you do the connection with RCA connector, this voltage 
  difference causes a surge to both equipment on the end of cable 
  (before the voltage difference gts nulled when groudn gets connected)
- laptop computer power supply is damaged and leaks mains power to PC 
  case, this gets though your witing to cable TV ground 

> 2) How could I prevent this kind of surge ?

Here are few tips:

- do the connections only when equipment are not powered up and 
  not plugged to wall
- run your PC preferably with it's internal battery only and not 
  connected to anything else (modem and Ethernet with UTP cable are OK, 
  USB connection to equipment with its own power supply is not a good idea)
- do the connections so that you always the ground gets connected 
  before the signal itself (might need you to used special RCA 
  connectors or adaters to BNC connections etc..)

Best if yuo can use all of those tips... Sometimes you can only 
follow some of them and you need to take your changes...

> 3) Should I never try to connect a laptop to a TV ?

With a properly caefully done connection will work well... 

> I made a diagram of my living room electrical setup. You can see it at
> this URL : http://home.ca.inter.net/~gdupuis/livingroomsetup.jpg
> 
> I don't think that the problem is from my TV since it is almost new and
> because it never fried my DVD player or VCR. I guess the problem comes
> from my laptop, but I still don't really understand.

The problem could in any equiopment or your house wiring 
(antenna/cableTV/mains). 

> Any help would be greatly appreciated. I really need to understand
> since I don't know much about electricity.
> Thank you very much.

Hopefully my tips have helped you. 

> (By the way, I am very sorry for the poor English. It is not my
> language.)

Your message was very well readable and understandable English.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/