Nad Equipment failure and revival

[GregS]

I was fiddling with a Nad receiver over the weekend. I wanted
to check once again about obtaining an obosolete FM chip
I bought the receiver about 7 years ago. I might have rebuilt the power amp
section but the FM did not work and the chip got extremely hot.
I figured it was bad. Now 7 years later I fire it up and am surprised
it works. Not getting hot either. I'm thinking 3 possibilities.

Possible short or power supply problem.
Capacitors doing something different.
Spontanious resurection of the chip.

??

greg

 

[William Sommerwerck]

There might have been a short on the PC board (such as a stray wire end)
that caused the wrong voltage to get to the wrong pin of the chip. I saw
this happen once with an op amp in a kit I was assembling. When I removed
the solder blob, it worked fine.

 

[GregS]

In article <h7ha81$qkb$1@news.eternal-september.org>, "William Sommerwerck" <grizzledgeezer@comcast.net> wrote:

There might have been a short on the PC board (such as a stray wire end)
that caused the wrong voltage to get to the wrong pin of the chip. I saw
this happen once with an op amp in a kit I was assembling. When I removed
the solder blob, it worked fine.

The equipment has moved around since way back, several times.
There is a layer of dust on the uncovered equipment but
I don't think that helped anything. Something to keep in mind though !

I got some other Nad stuff to fix. Nasty how some of the traces have melted
in some cases. I bought all this broken stuff on Ebay.

greg

 

[Allodoxaphobia]

On Mon, 31 Aug 2009 16:25:53 GMT, GregS wrote:

I was fiddling with a Nad receiver over the weekend. I wanted
to check once again about obtaining an obosolete FM chip
I bought the receiver about 7 years ago. I might have rebuilt the power amp
section but the FM did not work and the chip got extremely hot.
I figured it was bad. Now 7 years later I fire it up and am surprised
it works. Not getting hot either. I'm thinking 3 possibilities.

Possible short or power supply problem.
Capacitors doing something different.
Spontanious resurection of the chip.

4. A memory as reliable as mine.
5. Leprechauns

 

[Dave Platt]

There might have been a short on the PC board (such as a stray wire end)
that caused the wrong voltage to get to the wrong pin of the chip. I saw
this happen once with an op amp in a kit I was assembling. When I removed
the solder blob, it worked fine.

One failure mode I observed in a NAD stereo some years ago, was
a slanted resistor. A lot of the through-hole resistors were mounted
in the upright board-space-saving orientation. One of these had been
pushed (or had drooped naturally) far enough off of the vertical, that
the wire lead running to its upper end was contacting the lead on the
component next to it. Tapping on the board elicited quite a lot of
popping and crackling from the speaker, and some sparks from the
errant resistor... quite easy to locate it!

Bending the resistor back to vertical fixed the problem, and the
receiver worked fine (and still works, last time I checked it).

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[Gareth Magennis]

"GregS" <zekfrivo@zekfrivolous.com> wrote in message
news:h7gthu$99q$2@usenet01.srv.cis.pitt.edu...

I was fiddling with a Nad receiver over the weekend. I wanted
to check once again about obtaining an obosolete FM chip
I bought the receiver about 7 years ago. I might have rebuilt the power
amp
section but the FM did not work and the chip got extremely hot.
I figured it was bad. Now 7 years later I fire it up and am surprised
it works. Not getting hot either. I'm thinking 3 possibilities.

Possible short or power supply problem.
Capacitors doing something different.
Spontanious resurection of the chip.

??

greg

A lot of older equipment had loads of tantalum bypass capacitors on the
supply rails, one of which would short. One "bodge" method of finding
these was to send a large amount of current into the power supply rails via
a bench power supply. After a few seconds the shorted capacitor would
dissapear in a puff of smoke, thus identifying the culprit.
The point being that a shorted component might become open circuit any time
later.



Gareth.