TEAC Receiver with shorted analog switch chip

[Matt J. McCullar]

Recently I was asked to fix a TEAC home receiver/amplifier and I was able to
do so. I don't work on these things often, so I was surprised to find that
all of the RCA jack inputs (CD, tape, etc.) are routed through a couple of
integrated circuits that are essentially analog switches. This is how the
tin-can pushbutton switches on the front panel effectively choose which
inputs to amplify, instead of a direct mechanical switch selection.

One of these analog switch chips shorted out, making the right audio channel
put out much lower volume than the left -- no matter which audio source you
picked. Replacing the chip fixed the problem, but I'm still wondering what
caused the chip to fail in the first place.

My question is this: Because of these analog switch input chips, is it now
a good idea to turn off the power to the amplifier when installing or
removing the input audio cables? Perhaps a static spike zapped the chip; I
dunno. This unit didn't belong to me and I don't know the story of how the
thing failed.

Thanks!

 

[Mark D. Zacharias]

It's always been a good idea to have the power OFF when plugging /
unplugging cables. Better still to have the piece unplugged from the wall
entirely. Mech switch models still had the potential to loud pops or buzz
when the plugs were inserted or removed, and you've just reminded us of one
possible problem with digital switch IC's used this way.
More likely your friends' problem was caused by lightning/surge or plugging
some other device in there, like an electric guitar or an amp output which
exceeded the voltage rating of that input. Or the chip may have simply
failed for no good reason.

Wouldn't be a bad precaution to try to ground oneself to the chassis when
plugging in the inputs in the future - I may consider it after reading your
post. One could simply touch the metal chassis while at the same time
touching the outer ring of the RCA connector 'til one of them is seated.
That would prevent most problems that might arise from this.

Mark Z.


"Matt J. McCullar" <mccullar@flash.net> wrote in message
news:1clqb.19882$135.13012@newssvr32.news.prodigy.com...

Recently I was asked to fix a TEAC home receiver/amplifier and I was able
to
do so. I don't work on these things often, so I was surprised to find
that
all of the RCA jack inputs (CD, tape, etc.) are routed through a couple of
integrated circuits that are essentially analog switches. This is how the
tin-can pushbutton switches on the front panel effectively choose which
inputs to amplify, instead of a direct mechanical switch selection.

One of these analog switch chips shorted out, making the right audio
channel
put out much lower volume than the left -- no matter which audio source
you
picked. Replacing the chip fixed the problem, but I'm still wondering
what
caused the chip to fail in the first place.

My question is this: Because of these analog switch input chips, is it
now
a good idea to turn off the power to the amplifier when installing or
removing the input audio cables? Perhaps a static spike zapped the chip;
I
dunno. This unit didn't belong to me and I don't know the story of how
the
thing failed.

Thanks!

 

On Thu, 06 Nov 2003 11:30:57 GMT, "Mark D. Zacharias"
<mzacharias@nospam.earthlink.net> wrote:

It's always been a good idea to have the power OFF when plugging /
unplugging cables. Better still to have the piece unplugged from the wall
entirely.

I would think you would be better having all the equipment plugged in
so they are all at the same ground potential.

-Chris

 

[Mark D. Zacharias]

It probably wouldn't make any difference - especially if the Teac has a
"hard" power switch, but it's always been good advice to keep the receiver
unplugged from the wall until all your connections are made. Just reduces
the chances of anything _bad_ happening.

Mark Z.


<chris@nospam.com> wrote in message
news:55qoqvoga1gi40vovbahq631d60i0ig1lu@4ax.com...

On Thu, 06 Nov 2003 11:30:57 GMT, "Mark D. Zacharias"
mzacharias@nospam.earthlink.net> wrote:

It's always been a good idea to have the power OFF when plugging /
unplugging cables. Better still to have the piece unplugged from the wall
entirely.

I would think you would be better having all the equipment plugged in
so they are all at the same ground potential.

-Chris