Forums

Very interesting 'scoping results

Started by Unknown October 17, 2013
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.
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 -- 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
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 :-)
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 -- 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
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. >
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.
--- How would an isolation transformer have prevented that? -- JF