Sometimes, you just gotta get brutal ...

A

Arfa Daily

Guest
Had a JTS radio mic receiver on the bench today. "No power", said the job
ticket. With 12 volts going in, the output from the four-legged LDO 8 volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short. Nothing
getting hot because the regulator was in a full foldback condition. Loads of
surface mount 4558's in there, as well as a good selection of more exotic
ICs, and the 1.7 ohms could be measured at any of them. I had a quick word
with the shop that it came from, and the guy there was of the opinion that
it would not be worth pursuing even with the manufacturer, as it was well
out of warranty. "He'll just have to buy a new one" he said. That made me
feel bad, as I felt that I had perhaps not pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had already
been spent, I decided to get brutal with it, to see if I could make the
short show its face. I turned the power supply down to about 4 volts, and
linked across the regulator. I then turned the supply back on and settled
down to wait. As it turned out, it wasn't for very long ... A cloud of
smoke and sparks shot out of a tiny little surface mount solid tantalum 1uF
cap. There are hundreds of these - well, tens anyway! - all over the board.
It was but a few seconds work with the iron to whip this cap off the board.
The short disappeared with it, so I took my bridging link off the regulator,
and let it go back to working normally with a full 12 volt input. This time,
the output of the regulator was 7.96 volts, and the power LED lit. A quick
tune of the signal generator up to 863 MHz, with a bit of wire in the output
to act as an antenna, and the RF and AF LEDs lit. As a final check, I hooked
it into an amplifier, and got audio from the generator.

Sometimes it pays to persevere ... :)

Arfa
 
Arfa Daily wrote:
Had a JTS radio mic receiver on the bench today. "No power", said the
job ticket. With 12 volts going in, the output from the four-legged LDO
8 volt regulator, was almost nothing. A quick stab around with the
ohm-meter revealed about 1.7 ohms across the output. Nothing obviously
short. Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any
of them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with
the manufacturer, as it was well out of warranty. "He'll just have to
buy a new one" he said. That made me feel bad, as I felt that I had
perhaps not pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back on
and settled down to wait. As it turned out, it wasn't for very long
... A cloud of smoke and sparks shot out of a tiny little surface
mount solid tantalum 1uF cap. There are hundreds of these - well, tens
anyway! - all over the board. It was but a few seconds work with the
iron to whip this cap off the board. The short disappeared with it, so I
took my bridging link off the regulator, and let it go back to working
normally with a full 12 volt input. This time, the output of the
regulator was 7.96 volts, and the power LED lit. A quick tune of the
signal generator up to 863 MHz, with a bit of wire in the output to act
as an antenna, and the RF and AF LEDs lit. As a final check, I hooked it
into an amplifier, and got audio from the generator.

Sometimes it pays to persevere ... :)

Arfa
Click to expand...
Or you could track down a Shortsqueek by Global Specialties Model
SQ-1.Made in the 1970s and 80s it is a handy device to keep to track
down shorts on PCBs. Using a small op-amp that changes pitch depending
on how low the resistance is you can find shorts such as you describe
fairly quickly as long as your ear is good for tone changes of a few
Hertz. Polar Devices (UK) made Tone Ohm which was a similar device (I
need a probe if anyone has a spare) that I haven't been able to test
(because I'm missing the probe!).

Here is the manual for Shortsqueek (470k PDF)

http://www.flippers.com/pdfs/GlobalSpecialities_ShortSqueek_Model_SQ-1.pdf

These turn up on eBay from time to time - I bought two for my shop and
they do save hours of time (and chopping traces) every now and then...

John :-#)#


--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
 
Arfa Daily wrote:
Had a JTS radio mic receiver on the bench today. "No power", said the job
ticket. With 12 volts going in, the output from the four-legged LDO 8 volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short. Nothing
getting hot because the regulator was in a full foldback condition. Loads of
surface mount 4558's in there, as well as a good selection of more exotic
ICs, and the 1.7 ohms could be measured at any of them. I had a quick word
with the shop that it came from, and the guy there was of the opinion that
it would not be worth pursuing even with the manufacturer, as it was well
out of warranty. "He'll just have to buy a new one" he said. That made me
feel bad, as I felt that I had perhaps not pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had already
been spent, I decided to get brutal with it, to see if I could make the
short show its face. I turned the power supply down to about 4 volts, and
linked across the regulator. I then turned the supply back on and settled
down to wait. As it turned out, it wasn't for very long ... A cloud of
smoke and sparks shot out of a tiny little surface mount solid tantalum 1uF
cap. There are hundreds of these - well, tens anyway! - all over the board.
It was but a few seconds work with the iron to whip this cap off the board.
The short disappeared with it, so I took my bridging link off the regulator,
and let it go back to working normally with a full 12 volt input. This time,
the output of the regulator was 7.96 volts, and the power LED lit. A quick
tune of the signal generator up to 863 MHz, with a bit of wire in the output
to act as an antenna, and the RF and AF LEDs lit. As a final check, I hooked
it into an amplifier, and got audio from the generator.

Sometimes it pays to persevere ... :)
Click to expand...

I used to use a current limited power supply and a 4.5 digit voltmeter
to track the voltage drop on power rails. You would see larger voltage
drops till you reached the short, and smaller ones after that. I did
this at the factor on boards that cost us $8000 in components to stuff,
so I had to use non destructive testing.


--
You can't have a sense of humor, if you have no sense.
 
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in
news:ayv0r.137413$R65.96955@newsfe04.ams2:

Had a JTS radio mic receiver on the bench today. "No power", said the
job ticket. With 12 volts going in, the output from the four-legged
LDO 8 volt regulator, was almost nothing. A quick stab around with the
ohm-meter revealed about 1.7 ohms across the output. Nothing obviously
short. Nothing getting hot because the regulator was in a full
foldback condition. Loads of surface mount 4558's in there, as well as
a good selection of more exotic ICs, and the 1.7 ohms could be
measured at any of them. I had a quick word with the shop that it came
from, and the guy there was of the opinion that it would not be worth
pursuing even with the manufacturer, as it was well out of warranty.
"He'll just have to buy a new one" he said. That made me feel bad, as
I felt that I had perhaps not pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about
4 volts, and linked across the regulator. I then turned the supply
back on and settled down to wait. As it turned out, it wasn't for very
long ... A cloud of smoke and sparks shot out of a tiny little
surface mount solid tantalum 1uF cap. There are hundreds of these -
well, tens anyway! - all over the board. It was but a few seconds work
with the iron to whip this cap off the board. The short disappeared
with it, so I took my bridging link off the regulator, and let it go
back to working normally with a full 12 volt input. This time, the
output of the regulator was 7.96 volts, and the power LED lit. A quick
tune of the signal generator up to 863 MHz, with a bit of wire in the
output to act as an antenna, and the RF and AF LEDs lit. As a final
check, I hooked it into an amplifier, and got audio from the
generator.

Sometimes it pays to persevere ... :)

Arfa
Click to expand...
Ive done the same thing on TEK scopes.
sometimes,I paralleled the current limit resistor on a supply with another
R to increase the current output and see what smokes or pops. those glass
axial ceramic caps would pop,the dipped tantalums would smoke.
Sometimes,the scope would begin working,because the current limit was right
at the hairy edge.
I found a series pass XSTR with a bad B-E junction that way.It affected the
current limit point.

--
Jim Yanik
jyanik
at
localnet
dot com
 
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:ayv0r.137413$R65.96955@newsfe04.ams2...
Had a JTS radio mic receiver on the bench today. "No power", said the job
ticket. With 12 volts going in, the output from the four-legged LDO 8 volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short.
Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any of
them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with the
manufacturer, as it was well out of warranty. "He'll just have to buy a
new one" he said. That made me feel bad, as I felt that I had perhaps not
pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back on
and settled down to wait. As it turned out, it wasn't for very long ...
A cloud of smoke and sparks shot out of a tiny little surface mount solid
tantalum 1uF cap.
Click to expand...
That method has located many S/C zeners for me.
 
On Mon, 20 Feb 2012 17:38:14 -0000, "Arfa Daily"
<arfa.daily@ntlworld.com> put finger to keyboard and composed:

On the basis that the job wasn't going anywhere anyway, and time had already
been spent, I decided to get brutal with it, to see if I could make the
short show its face. I turned the power supply down to about 4 volts, and
linked across the regulator. I then turned the supply back on and settled
down to wait. As it turned out, it wasn't for very long ... A cloud of
smoke and sparks shot out of a tiny little surface mount solid tantalum 1uF
cap.
Click to expand...
Nice work!

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
"Arfa Daily"
Had a JTS radio mic receiver on the bench today. "No power", said the job
ticket. With 12 volts going in, the output from the four-legged LDO 8 volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short.
Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any of
them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with the
manufacturer, as it was well out of warranty. "He'll just have to buy a
new one" he said. That made me feel bad, as I felt that I had perhaps not
pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back on
and settled down to wait. As it turned out, it wasn't for very long ...
A cloud of smoke and sparks shot out of a tiny little surface mount solid
tantalum 1uF cap. There are hundreds of these - well, tens anyway! - all
over the board. It was but a few seconds work with the iron to whip this
cap off the board. The short disappeared with it, so I took my bridging
link off the regulator, and let it go back to working normally with a full
12 volt input. This time, the output of the regulator was 7.96 volts, and
the power LED lit. A quick tune of the signal generator up to 863 MHz,
with a bit of wire in the output to act as an antenna, and the RF and AF
LEDs lit. As a final check, I hooked it into an amplifier, and got audio
from the generator.

Sometimes it pays to persevere ... :)
Click to expand...

** This is known as the " tune for maximum smoke " method.

Often shows up short circuit bypass ceramics and regular pigtail tantalums
too.

How come you did not have the matching transmitter ??

I always insist on customers including them - more than once I have been
given a mic and receiver pair that do not work because they are on different
frequencies.


..... Phil
 
Ian Field <gangprobing.alien@ntlworld.com> wrote in message
news:vny0r.179314$WX2.157486@newsfe28.ams2...
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:ayv0r.137413$R65.96955@newsfe04.ams2...
Had a JTS radio mic receiver on the bench today. "No power", said the
job
ticket. With 12 volts going in, the output from the four-legged LDO 8
volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short.
Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any
of
them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with
the
manufacturer, as it was well out of warranty. "He'll just have to buy a
new one" he said. That made me feel bad, as I felt that I had perhaps
not
pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back on
and settled down to wait. As it turned out, it wasn't for very long ...
A cloud of smoke and sparks shot out of a tiny little surface mount
solid
tantalum 1uF cap.

That method has located many S/C zeners for me.
Click to expand...

A non contact IR thermometer can be useful for such and similar low ohmic
VTS , to wave over the errant board
 
On Mon, 20 Feb 2012 17:38:14 -0000 "Arfa Daily" <arfa.daily@ntlworld.com>
wrote in Message id: <ayv0r.137413$R65.96955@newsfe04.ams2>:

Had a JTS radio mic receiver on the bench today. "No power", said the job
ticket. With 12 volts going in, the output from the four-legged LDO 8 volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short. Nothing
getting hot because the regulator was in a full foldback condition. Loads of
surface mount 4558's in there, as well as a good selection of more exotic
ICs, and the 1.7 ohms could be measured at any of them. I had a quick word
with the shop that it came from, and the guy there was of the opinion that
it would not be worth pursuing even with the manufacturer, as it was well
out of warranty. "He'll just have to buy a new one" he said. That made me
feel bad, as I felt that I had perhaps not pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had already
been spent, I decided to get brutal with it, to see if I could make the
short show its face. I turned the power supply down to about 4 volts, and
linked across the regulator. I then turned the supply back on and settled
down to wait. As it turned out, it wasn't for very long ... A cloud of
smoke and sparks shot out of a tiny little surface mount solid tantalum 1uF
cap. There are hundreds of these - well, tens anyway! - all over the board.
It was but a few seconds work with the iron to whip this cap off the board.
The short disappeared with it, so I took my bridging link off the regulator,
and let it go back to working normally with a full 12 volt input. This time,
the output of the regulator was 7.96 volts, and the power LED lit. A quick
tune of the signal generator up to 863 MHz, with a bit of wire in the output
to act as an antenna, and the RF and AF LEDs lit. As a final check, I hooked
it into an amplifier, and got audio from the generator.

Sometimes it pays to persevere ... :)
Click to expand...
You could also try using a good four wire DMM set to measure resistance. I
use a Keithley 2000 which gives me resolution down to 100 micro-ohms.
 
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:ayv0r.137413$R65.96955@newsfe04.ams2...
Had a JTS radio mic receiver on the bench today. "No power", said the job
ticket. With 12 volts going in, the output from the four-legged LDO 8 volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short.
Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any of
them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with the
manufacturer, as it was well out of warranty. "He'll just have to buy a
new one" he said. That made me feel bad, as I felt that I had perhaps not
pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back on
and settled down to wait. As it turned out, it wasn't for very long ...
A cloud of smoke and sparks shot out of a tiny little surface mount solid
tantalum 1uF cap. There are hundreds of these - well, tens anyway! - all
over the board. It was but a few seconds work with the iron to whip this
cap off the board. The short disappeared with it, so I took my bridging
link off the regulator, and let it go back to working normally with a full
12 volt input. This time, the output of the regulator was 7.96 volts, and
the power LED lit. A quick tune of the signal generator up to 863 MHz,
with a bit of wire in the output to act as an antenna, and the RF and AF
LEDs lit. As a final check, I hooked it into an amplifier, and got audio
from the generator.

Sometimes it pays to persevere ... :)

Arfa
Click to expand...

I do this sometimes, but occasionally:

a.) The short will burn itself open, or

b.) The short is really zero point zero ohms and you start burning foil runs
before any component reveals itself by getting hot.

I might try the current limited method next time, but those very small
voltage differences may be a problem. I don't own such a DC supply though,
I'd have to use an actual resistor.

Might also be a good excuse to buy a non-contact thermometer ;-)

Mark Z.
 
Mark Zacharias <mark_zacharias@labolgcbs.net> wrote in message
news:4f43780f$0$32464$4c5efc6d@fastusenet.org...
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:ayv0r.137413$R65.96955@newsfe04.ams2...
Had a JTS radio mic receiver on the bench today. "No power", said the
job
ticket. With 12 volts going in, the output from the four-legged LDO 8
volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short.
Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any
of
them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with
the
manufacturer, as it was well out of warranty. "He'll just have to buy a
new one" he said. That made me feel bad, as I felt that I had perhaps
not
pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back on
and settled down to wait. As it turned out, it wasn't for very long ...
A cloud of smoke and sparks shot out of a tiny little surface mount
solid
tantalum 1uF cap. There are hundreds of these - well, tens anyway! - all
over the board. It was but a few seconds work with the iron to whip this
cap off the board. The short disappeared with it, so I took my bridging
link off the regulator, and let it go back to working normally with a
full
12 volt input. This time, the output of the regulator was 7.96 volts,
and
the power LED lit. A quick tune of the signal generator up to 863 MHz,
with a bit of wire in the output to act as an antenna, and the RF and AF
LEDs lit. As a final check, I hooked it into an amplifier, and got audio
from the generator.

Sometimes it pays to persevere ... :)

Arfa


I do this sometimes, but occasionally:

a.) The short will burn itself open, or

b.) The short is really zero point zero ohms and you start burning foil
runs
before any component reveals itself by getting hot.

I might try the current limited method next time, but those very small
voltage differences may be a problem. I don't own such a DC supply though,
I'd have to use an actual resistor.

Might also be a good excuse to buy a non-contact thermometer ;-)

Mark Z.
Click to expand...

I would recommend one, useful for zeroing in on failing caps in SMPS also,
no probes anywhere near any HV. Use on the Fahrenheit scale for more
resolution.
Try along the wall of TVs in an electronics retail barn is quite an eye
opener (makers never seem to specify electricity consumption so this is a
good proxy).
I'm surprised the cops don't dish them out to beat officers - much cheaper
than flying FLIR choppers/planes to pick up skunk factories (another thing
to try by walking along a street - noticeable variation in heat loss between
brick & windows etc).
 
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:ayv0r.137413$R65.96955@newsfe04.ams2...
Had a JTS radio mic receiver on the bench today. "No power", said the job
ticket. With 12 volts going in, the output from the four-legged LDO 8 volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short.
Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any of
them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with the
manufacturer, as it was well out of warranty. "He'll just have to buy a
new one" he said. That made me feel bad, as I felt that I had perhaps not
pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back on
and settled down to wait. As it turned out, it wasn't for very long ...
A cloud of smoke and sparks shot out of a tiny little surface mount solid
tantalum 1uF cap. There are hundreds of these - well, tens anyway! - all
over the board. It was but a few seconds work with the iron to whip this
cap off the board. The short disappeared with it, so I took my bridging
link off the regulator, and let it go back to working normally with a full
12 volt input. This time, the output of the regulator was 7.96 volts, and
the power LED lit. A quick tune of the signal generator up to 863 MHz,
with a bit of wire in the output to act as an antenna, and the RF and AF
LEDs lit. As a final check, I hooked it into an amplifier, and got audio
from the generator.

Sometimes it pays to persevere ... :)

Arfa
Click to expand...


Behringer 24 channel M8000 Eurodesks used to regularly come in with one of
the 100's (if not 1000's) of 17v rail bypass capacitors shorted. I used to
stick 5 amps from a bench supply down the offending rail, and it would
disappear in a puff of smoke within 10 seconds.

Although not strictly a pro repair, I always told the customer what I was
going to do, how much it would cost, and how much it would cost if I had to
dismantle the whole desk instead and conduct a proper search.
Not one chose the dismantling route, funnily enough.



Gareth.
 
Gareth Magennis <sound.service@btconnect.com> wrote in message
news:pYqdnQ7pNqV2J97SnZ2dnUVZ8lqdnZ2d@bt.com...
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:ayv0r.137413$R65.96955@newsfe04.ams2...
Had a JTS radio mic receiver on the bench today. "No power", said the
job
ticket. With 12 volts going in, the output from the four-legged LDO 8
volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short.
Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any
of
them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with
the
manufacturer, as it was well out of warranty. "He'll just have to buy a
new one" he said. That made me feel bad, as I felt that I had perhaps
not
pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back on
and settled down to wait. As it turned out, it wasn't for very long ...
A cloud of smoke and sparks shot out of a tiny little surface mount
solid
tantalum 1uF cap. There are hundreds of these - well, tens anyway! - all
over the board. It was but a few seconds work with the iron to whip this
cap off the board. The short disappeared with it, so I took my bridging
link off the regulator, and let it go back to working normally with a
full
12 volt input. This time, the output of the regulator was 7.96 volts,
and
the power LED lit. A quick tune of the signal generator up to 863 MHz,
with a bit of wire in the output to act as an antenna, and the RF and AF
LEDs lit. As a final check, I hooked it into an amplifier, and got audio
from the generator.

Sometimes it pays to persevere ... :)

Arfa



Behringer 24 channel M8000 Eurodesks used to regularly come in with one of
the 100's (if not 1000's) of 17v rail bypass capacitors shorted. I used
to
stick 5 amps from a bench supply down the offending rail, and it would
disappear in a puff of smoke within 10 seconds.

Although not strictly a pro repair, I always told the customer what I was
going to do, how much it would cost, and how much it would cost if I had
to
dismantle the whole desk instead and conduct a proper search.
Not one chose the dismantling route, funnily enough.



Gareth.
Click to expand...

If these were MLCC caps then maybe no less than .2 ohm or so , so a chance
an IR non contact thermometer would pick it up with only forcing an amp
through the rail, would save stressing the traces and leaving a time bomb in
the works
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ji0f9s$nkb$1@dont-email.me...
Gareth Magennis <sound.service@btconnect.com> wrote in message
news:pYqdnQ7pNqV2J97SnZ2dnUVZ8lqdnZ2d@bt.com...

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:ayv0r.137413$R65.96955@newsfe04.ams2...
Had a JTS radio mic receiver on the bench today. "No power", said the
job
ticket. With 12 volts going in, the output from the four-legged LDO 8
volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short.
Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any
of
them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with
the
manufacturer, as it was well out of warranty. "He'll just have to buy a
new one" he said. That made me feel bad, as I felt that I had perhaps
not
pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back
on
and settled down to wait. As it turned out, it wasn't for very long ...
A cloud of smoke and sparks shot out of a tiny little surface mount
solid
tantalum 1uF cap. There are hundreds of these - well, tens anyway! -
all
over the board. It was but a few seconds work with the iron to whip
this
cap off the board. The short disappeared with it, so I took my bridging
link off the regulator, and let it go back to working normally with a
full
12 volt input. This time, the output of the regulator was 7.96 volts,
and
the power LED lit. A quick tune of the signal generator up to 863 MHz,
with a bit of wire in the output to act as an antenna, and the RF and
AF
LEDs lit. As a final check, I hooked it into an amplifier, and got
audio
from the generator.

Sometimes it pays to persevere ... :)

Arfa



Behringer 24 channel M8000 Eurodesks used to regularly come in with one
of
the 100's (if not 1000's) of 17v rail bypass capacitors shorted. I used
to
stick 5 amps from a bench supply down the offending rail, and it would
disappear in a puff of smoke within 10 seconds.

Although not strictly a pro repair, I always told the customer what I was
going to do, how much it would cost, and how much it would cost if I had
to
dismantle the whole desk instead and conduct a proper search.
Not one chose the dismantling route, funnily enough.



Gareth.




If these were MLCC caps then maybe no less than .2 ohm or so , so a chance
an IR non contact thermometer would pick it up with only forcing an amp
through the rail, would save stressing the traces and leaving a time bomb
in
the works
Click to expand...


I suspect the remaining 999 capacitors were far more of a time bomb - this
was a regular occurrence.



Gareth.
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:jhvkm2$4jn$1@dont-email.me...
Ian Field <gangprobing.alien@ntlworld.com> wrote in message
news:vny0r.179314$WX2.157486@newsfe28.ams2...

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:ayv0r.137413$R65.96955@newsfe04.ams2...
Had a JTS radio mic receiver on the bench today. "No power", said the
job
ticket. With 12 volts going in, the output from the four-legged LDO 8
volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short.
Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any
of
them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with
the
manufacturer, as it was well out of warranty. "He'll just have to buy a
new one" he said. That made me feel bad, as I felt that I had perhaps
not
pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back
on
and settled down to wait. As it turned out, it wasn't for very long ...
A cloud of smoke and sparks shot out of a tiny little surface mount
solid
tantalum 1uF cap.

That method has located many S/C zeners for me.




A non contact IR thermometer can be useful for such and similar low ohmic
VTS , to wave over the errant board
Click to expand...

Maplin didn't stock those back in the days when I used brute force &
ignorance to weed out dud zeners.
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:9qgl88FfevU1@mid.individual.net...
"Arfa Daily"

Had a JTS radio mic receiver on the bench today. "No power", said the job
ticket. With 12 volts going in, the output from the four-legged LDO 8
volt regulator, was almost nothing. A quick stab around with the
ohm-meter revealed about 1.7 ohms across the output. Nothing obviously
short. Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any
of them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with
the manufacturer, as it was well out of warranty. "He'll just have to buy
a new one" he said. That made me feel bad, as I felt that I had perhaps
not pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back on
and settled down to wait. As it turned out, it wasn't for very long ... A
cloud of smoke and sparks shot out of a tiny little surface mount solid
tantalum 1uF cap. There are hundreds of these - well, tens anyway! - all
over the board. It was but a few seconds work with the iron to whip this
cap off the board. The short disappeared with it, so I took my bridging
link off the regulator, and let it go back to working normally with a
full 12 volt input. This time, the output of the regulator was 7.96
volts, and the power LED lit. A quick tune of the signal generator up to
863 MHz, with a bit of wire in the output to act as an antenna, and the
RF and AF LEDs lit. As a final check, I hooked it into an amplifier, and
got audio from the generator.

Sometimes it pays to persevere ... :)


** This is known as the " tune for maximum smoke " method.

Often shows up short circuit bypass ceramics and regular pigtail tantalums
too.

How come you did not have the matching transmitter ??

I always insist on customers including them - more than once I have been
given a mic and receiver pair that do not work because they are on
different frequencies.


.... Phil
Click to expand...

This work comes from a music shop. Usually, if it seems to be an RF issue,
they will send both bits to me. In this instance, as the receive unit was
obviously dead, that was all that the owner brought in. They pulled it apart
in the shop, in case there was a fuse to try, but once they saw that there
wasn't, they just shipped it out to me, knowing that I have a decent HP
generator that's good to 2.4 GHz. I do not see any that are a channel
mis-match issue, because that sort of thing is filtered in the shop. The guy
that owns the shop is fairly technical and can deal with testing and
replacing valves. He is able to replace HF drivers, and has been a bass unit
re-coner for years. But he knows his limitations, and anything beyond that,
is just passed out to me.

Oddly, a couple of months ago, I had two radio mic receivers in the space of
a couple of weeks, which both had the demodulator tank mis-tuned by a good
half turn. Neither had been 'got-at' as far as we know, and both remained
stable and correctly tuned over a soak test of several days. Neither has
come bouncing back either, so it's a bit of a mystery as to why they were
like it.

Arfa
 
"Mark Zacharias" <mark_zacharias@labolgcbs.net> wrote in message
news:4f43780f$0$32464$4c5efc6d@fastusenet.org...
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:ayv0r.137413$R65.96955@newsfe04.ams2...
Had a JTS radio mic receiver on the bench today. "No power", said the job
ticket. With 12 volts going in, the output from the four-legged LDO 8
volt regulator, was almost nothing. A quick stab around with the
ohm-meter revealed about 1.7 ohms across the output. Nothing obviously
short. Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any
of them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with
the manufacturer, as it was well out of warranty. "He'll just have to buy
a new one" he said. That made me feel bad, as I felt that I had perhaps
not pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back on
and settled down to wait. As it turned out, it wasn't for very long ... A
cloud of smoke and sparks shot out of a tiny little surface mount solid
tantalum 1uF cap. There are hundreds of these - well, tens anyway! - all
over the board. It was but a few seconds work with the iron to whip this
cap off the board. The short disappeared with it, so I took my bridging
link off the regulator, and let it go back to working normally with a
full 12 volt input. This time, the output of the regulator was 7.96
volts, and the power LED lit. A quick tune of the signal generator up to
863 MHz, with a bit of wire in the output to act as an antenna, and the
RF and AF LEDs lit. As a final check, I hooked it into an amplifier, and
got audio from the generator.

Sometimes it pays to persevere ... :)

Arfa


I do this sometimes, but occasionally:

a.) The short will burn itself open, or

b.) The short is really zero point zero ohms and you start burning foil
runs before any component reveals itself by getting hot.

I might try the current limited method next time, but those very small
voltage differences may be a problem. I don't own such a DC supply though,
I'd have to use an actual resistor.

Might also be a good excuse to buy a non-contact thermometer ;-)

Mark Z.
Click to expand...
I actually have a non-contact IR thermometer, and it's just about OK on
biggish items like chips, but nothing like tight enough on its sensing area,
to be able to detect a gnat's bollock cap getting hot !

Arfa
 
On Wed, 22 Feb 2012 02:36:14 -0000, "Arfa Daily"
<arfa.daily@ntlworld.com> wrote:

I actually have a non-contact IR thermometer, and it's just about OK on
biggish items like chips, but nothing like tight enough on its sensing area,
to be able to detect a gnat's bollock cap getting hot !
Click to expand...
I made an attachment that resembles a black (non-reflective) soda
straw, about 8 mm in diameter. It is fitted to the lens on my IR
thermometer with an ugly mess of electrical tape. The idea is for
only the light coming down the soda straw to hit the pyrometer. Works
fine for measuring individual components (although the readings appear
to be lower than expected).

Got $2,000 and up?
<http://www.flir.com/cvs/americas/en/personalvision/view/?id=44756>

I like your "big bang" method of troubleshooting. I've used when
desperate, with variable success. In one case, I destroyed a
transceiver when the PCB traces decided to immitate a fuse. Other
times, it clearly identified a shorted capacitor, by exploding.
Tantalums are rather interesting, producing a bright red glow, and
belching toxic fumes.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS
 
Jeff Liebermann <jeffl@cruzio.com> wrote in message
news:siq8k7tf9755g2605m2auib1aan69o6kgs@4ax.com...
On Wed, 22 Feb 2012 02:36:14 -0000, "Arfa Daily"
arfa.daily@ntlworld.com> wrote:

I actually have a non-contact IR thermometer, and it's just about OK on
biggish items like chips, but nothing like tight enough on its sensing
area,
to be able to detect a gnat's bollock cap getting hot !

I made an attachment that resembles a black (non-reflective) soda
straw, about 8 mm in diameter. It is fitted to the lens on my IR
thermometer with an ugly mess of electrical tape. The idea is for
only the light coming down the soda straw to hit the pyrometer. Works
fine for measuring individual components (although the readings appear
to be lower than expected).

Got $2,000 and up?
http://www.flir.com/cvs/americas/en/personalvision/view/?id=44756

I like your "big bang" method of troubleshooting. I've used when
desperate, with variable success. In one case, I destroyed a
transceiver when the PCB traces decided to immitate a fuse. Other
times, it clearly identified a shorted capacitor, by exploding.
Tantalums are rather interesting, producing a bright red glow, and
belching toxic fumes.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS
Click to expand...

I tried that a couple of years back and found what you found and by
experiment no better resolution with or without the shroud, so went back to
plain unshrouded and localising to area rather than individual SMD
 
Arfa Daily wrote:


Oddly, a couple of months ago, I had two radio mic receivers in the space
of a couple of weeks, which both had the demodulator tank mis-tuned by a
good half turn. Neither had been 'got-at' as far as we know, and both
remained stable and correctly tuned over a soak test of several days.
Neither has come bouncing back either, so it's a bit of a mystery as to
why they were like it.
Same make of unit? Sounds like a screw-up at the factory, and really weak
Click to expand...
QC. Somebody had the wrong tuning procedure, or the transmitter they were
using to tune it was set to the wrong freq.

Well, that's China for you.

Jon
 
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