Very interesting 'scoping results

Guest
At least interesting to me. On the advice from members of this
newsgroup I bought a 465B TEK oscilloscope. It comes in handy now and
then. Yesterday I had to replace a power supply in one of my CNC
machines. The only one available in a reasonable length of time was a
used one of unknown quality. I spoke to a friend of mine and he said
to 'scope the thing and look for any ripple on the DC outputs. He said
there should be no ripple. I powered up the power supply with a variac
and watched the 'scope display as the power supplied rose. When the
power supply started to sing a little there was 3.5 volts out from the
5 volt output and there was lots of sawtooth shaped ripple. As the
input voltage rose the volts out went to 5 volts and the 'scope showed
a flat line. Even when the display was at .1 volts per division. Man,
that was so cool. I checked all the outputs and they were all flat.
Sure made me feel good and it sure is neat using an oscilloscope to
watch what's happening.
Eric
 
On 10/17/2013 4:51 PM, etpm@whidbey.com wrote:
At least interesting to me. On the advice from members of this
newsgroup I bought a 465B TEK oscilloscope. It comes in handy now and
then. Yesterday I had to replace a power supply in one of my CNC
machines. The only one available in a reasonable length of time was a
used one of unknown quality. I spoke to a friend of mine and he said
to 'scope the thing and look for any ripple on the DC outputs. He said
there should be no ripple. I powered up the power supply with a variac
and watched the 'scope display as the power supplied rose. When the
power supply started to sing a little there was 3.5 volts out from the
5 volt output and there was lots of sawtooth shaped ripple. As the
input voltage rose the volts out went to 5 volts and the 'scope showed
a flat line. Even when the display was at .1 volts per division. Man,
that was so cool. I checked all the outputs and they were all flat.
Sure made me feel good and it sure is neat using an oscilloscope to
watch what's happening.
Eric

I happy that you enjoyed that.
Click to expand...
 
On 10/17/2013 04:51 PM, etpm@whidbey.com wrote:
At least interesting to me. On the advice from members of this
newsgroup I bought a 465B TEK oscilloscope. It comes in handy now and
then. Yesterday I had to replace a power supply in one of my CNC
machines. The only one available in a reasonable length of time was a
used one of unknown quality. I spoke to a friend of mine and he said
to 'scope the thing and look for any ripple on the DC outputs. He said
there should be no ripple. I powered up the power supply with a variac
and watched the 'scope display as the power supplied rose. When the
power supply started to sing a little there was 3.5 volts out from the
5 volt output and there was lots of sawtooth shaped ripple. As the
input voltage rose the volts out went to 5 volts and the 'scope showed
a flat line. Even when the display was at .1 volts per division. Man,
that was so cool. I checked all the outputs and they were all flat.
Sure made me feel good and it sure is neat using an oscilloscope to
watch what's happening.
Eric
Click to expand...

Good going. That's just what it's supposed to do. It's a bit
dangerous poking round inside line-powered supplies with a scope probe,
so if you're going to make a habit of it I'd recommend using an
isolation transformer as well.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On Mon, 21 Oct 2013 12:37:18 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 10/17/2013 04:51 PM, etpm@whidbey.com wrote:
At least interesting to me. On the advice from members of this
newsgroup I bought a 465B TEK oscilloscope. It comes in handy now and
then. Yesterday I had to replace a power supply in one of my CNC
machines. The only one available in a reasonable length of time was a
used one of unknown quality. I spoke to a friend of mine and he said
to 'scope the thing and look for any ripple on the DC outputs. He said
there should be no ripple. I powered up the power supply with a variac
and watched the 'scope display as the power supplied rose. When the
power supply started to sing a little there was 3.5 volts out from the
5 volt output and there was lots of sawtooth shaped ripple. As the
input voltage rose the volts out went to 5 volts and the 'scope showed
a flat line. Even when the display was at .1 volts per division. Man,
that was so cool. I checked all the outputs and they were all flat.
Sure made me feel good and it sure is neat using an oscilloscope to
watch what's happening.
Eric


Good going. That's just what it's supposed to do. It's a bit
dangerous poking round inside line-powered supplies with a scope probe,
so if you're going to make a habit of it I'd recommend using an
isolation transformer as well.

Cheers

Phil Hobbs
Click to expand...
Greetings Phil,
I was just checking the low voltage outputs. But now I have the bad
supply to check. I have not been able to find a schematic for it after
lots of looking and asking so I guess I will be poking around in it.
Why the isolation transformer?
Thanks,
Eric
 
On 22/10/13 05:38, etpm@whidbey.com wrote:
On Mon, 21 Oct 2013 12:37:18 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 10/17/2013 04:51 PM, etpm@whidbey.com wrote:
At least interesting to me. On the advice from members of this
newsgroup I bought a 465B TEK oscilloscope. It comes in handy now and
then. Yesterday I had to replace a power supply in one of my CNC
machines. The only one available in a reasonable length of time was a
used one of unknown quality. I spoke to a friend of mine and he said
to 'scope the thing and look for any ripple on the DC outputs. He said
there should be no ripple. I powered up the power supply with a variac
and watched the 'scope display as the power supplied rose. When the
power supply started to sing a little there was 3.5 volts out from the
5 volt output and there was lots of sawtooth shaped ripple. As the
input voltage rose the volts out went to 5 volts and the 'scope showed
a flat line. Even when the display was at .1 volts per division. Man,
that was so cool. I checked all the outputs and they were all flat.
Sure made me feel good and it sure is neat using an oscilloscope to
watch what's happening.
Eric


Good going. That's just what it's supposed to do. It's a bit
dangerous poking round inside line-powered supplies with a scope probe,
so if you're going to make a habit of it I'd recommend using an
isolation transformer as well.

Cheers

Phil Hobbs
Greetings Phil,
I was just checking the low voltage outputs. But now I have the bad
supply to check. I have not been able to find a schematic for it after
lots of looking and asking so I guess I will be poking around in it.
Why the isolation transformer?
Thanks,
Eric

That's to prevent flames from shooting out of your nether region :)
Click to expand...
 
On 10/21/2013 05:38 PM, etpm@whidbey.com wrote:
On Mon, 21 Oct 2013 12:37:18 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 10/17/2013 04:51 PM, etpm@whidbey.com wrote:
At least interesting to me. On the advice from members of this
newsgroup I bought a 465B TEK oscilloscope. It comes in handy now and
then. Yesterday I had to replace a power supply in one of my CNC
machines. The only one available in a reasonable length of time was a
used one of unknown quality. I spoke to a friend of mine and he said
to 'scope the thing and look for any ripple on the DC outputs. He said
there should be no ripple. I powered up the power supply with a variac
and watched the 'scope display as the power supplied rose. When the
power supply started to sing a little there was 3.5 volts out from the
5 volt output and there was lots of sawtooth shaped ripple. As the
input voltage rose the volts out went to 5 volts and the 'scope showed
a flat line. Even when the display was at .1 volts per division. Man,
that was so cool. I checked all the outputs and they were all flat.
Sure made me feel good and it sure is neat using an oscilloscope to
watch what's happening.
Eric


Good going. That's just what it's supposed to do. It's a bit
dangerous poking round inside line-powered supplies with a scope probe,
so if you're going to make a habit of it I'd recommend using an
isolation transformer as well.

Cheers

Phil Hobbs
Greetings Phil,
I was just checking the low voltage outputs. But now I have the bad
supply to check. I have not been able to find a schematic for it after
lots of looking and asking so I guess I will be poking around in it.
Why the isolation transformer?
Thanks,
Eric
Click to expand...

So you don't electrocute yourself by some fat-fingered move while poking
around inside. I almost did that when I was 14 years old, building a
1500V supply for a transmitter that I never finished. I accidentally
touched B+ with my right index finger while holding the chassis with my
left hand.

The power supply went through the window, dropped 2 stories and knocked
a couple of shingles off a porch roof before embedding itself in the
ground. (Still worked though.) I woke up leaning against the opposite
wall. If it had been a 400 volt supply, I might well have died, because
the spasm in my triceps might not have been strong enough to break my
grip, and of course moderately high voltages like that more commonly
cause heart fibrillation, because there isn't enough current to
completely reset the heart rhythm.

An isolation transformer won't save you from fat-fingeredness on that
scale, but it will usually keep you from frying yourself with the AC mains.

And keep one hand in your pocket.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On Tue, 22 Oct 2013 10:32:45 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 10/21/2013 05:38 PM, etpm@whidbey.com wrote:
On Mon, 21 Oct 2013 12:37:18 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 10/17/2013 04:51 PM, etpm@whidbey.com wrote:
At least interesting to me. On the advice from members of this
newsgroup I bought a 465B TEK oscilloscope. It comes in handy now and
then. Yesterday I had to replace a power supply in one of my CNC
machines. The only one available in a reasonable length of time was a
used one of unknown quality. I spoke to a friend of mine and he said
to 'scope the thing and look for any ripple on the DC outputs. He said
there should be no ripple. I powered up the power supply with a variac
and watched the 'scope display as the power supplied rose. When the
power supply started to sing a little there was 3.5 volts out from the
5 volt output and there was lots of sawtooth shaped ripple. As the
input voltage rose the volts out went to 5 volts and the 'scope showed
a flat line. Even when the display was at .1 volts per division. Man,
that was so cool. I checked all the outputs and they were all flat.
Sure made me feel good and it sure is neat using an oscilloscope to
watch what's happening.
Eric


Good going. That's just what it's supposed to do. It's a bit
dangerous poking round inside line-powered supplies with a scope probe,
so if you're going to make a habit of it I'd recommend using an
isolation transformer as well.

Cheers

Phil Hobbs
Greetings Phil,
I was just checking the low voltage outputs. But now I have the bad
supply to check. I have not been able to find a schematic for it after
lots of looking and asking so I guess I will be poking around in it.
Why the isolation transformer?
Thanks,
Eric


So you don't electrocute yourself by some fat-fingered move while poking
around inside. I almost did that when I was 14 years old, building a
1500V supply for a transmitter that I never finished. I accidentally
touched B+ with my right index finger while holding the chassis with my
left hand.

The power supply went through the window, dropped 2 stories and knocked
a couple of shingles off a porch roof before embedding itself in the
ground. (Still worked though.) I woke up leaning against the opposite
wall. If it had been a 400 volt supply, I might well have died, because
the spasm in my triceps might not have been strong enough to break my
grip, and of course moderately high voltages like that more commonly
cause heart fibrillation, because there isn't enough current to
completely reset the heart rhythm.

An isolation transformer won't save you from fat-fingeredness on that
scale, but it will usually keep you from frying yourself with the AC mains.

And keep one hand in your pocket.

Cheers

Phil Hobbs
Click to expand...
I thought the isolation transformer advice was being given because it
protects the oscilloscope. I do keep one hand in a pocket when
checking high voltages. After getting a few whopper shocks when I was
a kid I learned to respect electricity. Nevertheless, I will get an
isolation transformer to use when testing the bad power supply.
Eric
 
On Tue, 22 Oct 2013, Phil Hobbs wrote:


So you don't electrocute yourself by some fat-fingered move while poking
around inside. I almost did that when I was 14 years old, building a 1500V
supply for a transmitter that I never finished. I accidentally touched B+
with my right index finger while holding the chassis with my left hand.

The power supply went through the window, dropped 2 stories and knocked a
couple of shingles off a porch roof before embedding itself in the ground.
(Still worked though.) I woke up leaning against the opposite wall. If it
had been a 400 volt supply, I might well have died, because the spasm in my
triceps might not have been strong enough to break my grip, and of course
moderately high voltages like that more commonly cause heart fibrillation,
because there isn't enough current to completely reset the heart rhythm.
Click to expand...
The incident that made sure I was careful of high voltage in the future
was when I was about 14 too. I don't really remember the shock, I
remember banging my elbow against something, which hurt, as my arm jerked
away from the high voltage (which was a lower high voltage). It was the
hurt elbow that is the reason I'm more careful. Though I can (not so
vividly) remember that funny feeling from touching B+ and ground, so
different from the funny feeling when I accidentally put my fingers across
the 120VAC line.

The important thing is to hope the lesson comes early, because otherwise
it's fatal.

Michael
 
On Tue, 22 Oct 2013 12:54:43 +0800, Rheilly Phoull wrote:

> That's to prevent flames from shooting out of your nether region :)

Chance would be a fine thing ;-)

--
"Design is the reverse of analysis"
(R.D. Middlebrook)
 
On Tue, 22 Oct 2013 10:32:45 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 10/21/2013 05:38 PM, etpm@whidbey.com wrote:

Greetings Phil,
I was just checking the low voltage outputs. But now I have the bad
supply to check. I have not been able to find a schematic for it after
lots of looking and asking so I guess I will be poking around in it.
Why the isolation transformer?
Thanks,
Eric


So you don't electrocute yourself by some fat-fingered move while poking
around inside. I almost did that when I was 14 years old, building a
1500V supply for a transmitter that I never finished. I accidentally
touched B+ with my right index finger while holding the chassis with my
left hand.
Click to expand...

---
How would an isolation transformer have prevented that?

--
JF
 
On 10/22/2013 4:41 PM, John Fields wrote:
On Tue, 22 Oct 2013 10:32:45 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 10/21/2013 05:38 PM, etpm@whidbey.com wrote:

Greetings Phil,
I was just checking the low voltage outputs. But now I have the bad
supply to check. I have not been able to find a schematic for it after
lots of looking and asking so I guess I will be poking around in it.
Why the isolation transformer?
Thanks,
Eric


So you don't electrocute yourself by some fat-fingered move while poking
around inside. I almost did that when I was 14 years old, building a
1500V supply for a transmitter that I never finished. I accidentally
touched B+ with my right index finger while holding the chassis with my
left hand.

---
How would an isolation transformer have prevented that?
Click to expand...

It wouldn't, as I noted in the part you snipped. However, every bit helps.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058

hobbs at electrooptical dot net
http://electrooptical.net
 
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