Failure modes in sound cards

[Cydrome Leader]

Mark Zacharias <mark_zacharias@labolgcbs.net> wrote:

"Jeroni Paul" <JERONI.PAUL@terra.es> wrote in message
news:9164fb16-b71e-43c0-b54c-4072b6d4b8c2@googlegroups.com...
Mark Zacharias wrote:
Horseshit. It would make a loud hum noise - nothing worse.
I see this sort of thing all the time.

Wrong, this is very risky to do and I have seen lots of stuff damaged that
way. Common to >damage the inputs on TV scart sockets, TV outputs in video
cards, audio inputs and outputs, >etc.

I particularly hate RCA connectors, most of them have the center terminal
longer than the >ground so it is the first to contact when plugged. Very
dangerous situation if there is no other >link joining the grounds of both
devices. Audio jacks and F plugs suffer the same problem. >Other connectors
are somewhat better where ground usually contacts first like USB, DVI,
legacy PC ports (serial, parallel, VGA) and Scart. But do not rely on
that, connector design if >far from perfect in this regard.

To avoid nasty surprises I always plug sensitive cables with both devices
unplugged from >mains and have the precaution to momentarily touch grounds
first to discarge any static.


I'm with you on not plugging stuff in when powered. It's only common sense.

I stand by my statements however. Been repairing audio for more than 30
years, and have factory training from majors such as Sony, Yamaha, Pioneer,
NEC, Hitachi, Denon-Marantz, and others.

Any great stories of weird training or tips and tricks from any of these
companies?

I came across a operator/service manual for a machine that said buff and
shine the shiny mechanical parts with car polish or wax, and that the idea
came from customers, it seems like a good idea and so that's now suggested
as standard operating procedure for everybody.

 

[Cydrome Leader]

jurb6006@gmail.com wrote:

One thing to consider is that PCs are usually equipped with three prong cords which means they have an Earth ground. this means that all the line leakage of any connected equipment flows throught the commons, or grounds on anything like an audio cable, anything.

I had to deal with a wierd ground loop problem on a commercial projector because it was properly grounded and so was thre cable coming in. Turns out the guy had two ground rods installed and there apparently was a ground gradient. the guy is an electrician actually ! I had to build him an isolator. It came out of an old TV that had a hot chassis, all I had to do was attach the correct connector.

That happened because the projector was three prong, but can happen to anything else like that, if they do not go to the same ground.

In other words, your ground is not my ground.

Ground issues with parallel cables running to printers in other rooms was
always interesting. There's nothing like sparks when pluggin in a
centronics connector.

10base 2 networks had this issue too with everything all over the place
being grounded to each other.

 

[Mark Zacharias]

"Jeroni Paul" <JERONI.PAUL@terra.es> wrote in message
news:83d57a23-4c42-48ea-b10c-971ad3de7341@googlegroups.com...
While ground loop noise is fixed disconnecting grounds *one* ground *must*
remain connected so both chassis are at the same potential. In this case
both devices are properly grounded and no loud hum occurs.

But if one or both devices are not properly grounded and you do not connect
audio ground you will get a loud hum and you are asking for trouble. The
ungrounded device is being grounded through audio circuits. This is not OK
and may result in damage and you was not right when you said that was safe
to do.

Of course the danger level depends on the equipment used. Some people likes
to connect the PC to a music box that in turn is connected to a FM aerial
together with some TV sets and other equipment all of them ungrounded. In
this scenario many devices are grounded through the audio cable, a real
danger if it goes open or it is plugged/unplugged.


***************************************************************

(Windoze not quoting properly...)


Not dangerous to the user - just annoying for the noise, I have suspected,
but could not prove, that an FET at an input stage might have been damaged
by plugging and unplugging while powered. There was only 1K worth of input
protection on that unit, and I have seen several of that type with the FET
blown, hence my suspicion.

Mark Z.