Recognise this trace?

[Cursitor Doom]

Gentlemen,

The link below shows a scope trace of the output of a linear PSU (voltage
4.7VDC) with about 300mV of 100Hz ripple riding on it. This PSU is in-
circuit under load from the boards it supplies. Normally I would assume a
filter capacitor to be at fault here, but they all check out fine so
something else is causing this ripple. Note there is a characteristic
'knee' on the high peaks and I'm thinking this must be indicative of
*something* trouble is, I don't know what. If anyone recognises this
waveshape and knows what causes it, that'd be "awesome" - as our American
friends describe everything. Check it out:


https://www.flickr.com/photos/128859641@N02/35684682551/in/dateposted-
public/

 

[Foxs Mercantile]

On 7/9/2017 10:10 AM, Cursitor Doom wrote:

If anyone recognises this waveshape and knows what causes
it, that'd be "awesome"

Not sure what's causing it, but it's indicative of a non-
linear load. The "knee" is where the load transitions from
one value to a smaller value.



--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

---
This email has been checked for viruses by AVG.
http://www.avg.com

 

[Jeff Liebermann]

On Sun, 9 Jul 2017 15:10:46 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

>Gentlemen,

Surely, you jest.

The link below shows a scope trace of the output of a linear PSU (voltage
4.7VDC) with about 300mV of 100Hz ripple riding on it. This PSU is in-
circuit under load from the boards it supplies. Normally I would assume a
filter capacitor to be at fault here, but they all check out fine so
something else is causing this ripple. Note there is a characteristic
'knee' on the high peaks and I'm thinking this must be indicative of
*something* trouble is, I don't know what. If anyone recognises this
waveshape and knows what causes it, that'd be "awesome" - as our American
friends describe everything. Check it out:

https://www.flickr.com/photos/128859641@N02/35684682551/in/dateposted-public/

Is the mystery load the hardware appearing in adjacent photos? EXIF
says that they were taken 4 days earlier, which suggests a connection.

These photos looks odd:
<https://www.flickr.com/photos/128859641@N02/34892442244/in/photostream/>
<https://www.flickr.com/photos/128859641@N02/35564536392/in/photostream/>
because C17 (the 2nd blue electrolytic from the right) seems to have
been soldered into the wrong PCB holes. The white silk screen circle
makes a good target for installing capacitors. If my crystal ball is
correct, this capacitor might be presenting a higher than normal
current load to the power supply, which is reacting by producing
excessive ripple that you're seeing on the scope.

Is this the capacitor you removed from the board?
<https://www.flickr.com/photos/128859641@N02/35050368241/in/photostream/>
If so, you ripped out the plated through hole. 4 terminal radial caps
are not common, so I guess you substituted something else. What did
you put in its place? Did you test and fix the PCB traces?

Oh, never mind. I found your rather ugly solder wick PCB fix:
<https://www.flickr.com/photos/128859641@N02/35602405551/in/photostream/>
You might want to double (or triple) check your soldering and PCB
through hole connections.

From this photo:
<https://www.flickr.com/photos/128859641@N02/35564539582/in/photostream/>
there's a tuning screw, semi-rigid coax cable, and cavity filter on
the left side. Too bad the power supply board is missing. There are
some gold connector pins in the photo. So, what is it?


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

 

[Tim Williams]

If it's your signal generator thing, yes, it's very possible / likely to
have dried out caps (excess ESR).

Yes, the nippley appearance is likely ESR. But, if you say it's okay, then
it must be okay. Right?

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com

"Cursitor Doom" <curd@notformail.com> wrote in message
newsjth1m$vqg$1@dont-email.me...

Gentlemen,

The link below shows a scope trace of the output of a linear PSU (voltage
4.7VDC) with about 300mV of 100Hz ripple riding on it. This PSU is in-
circuit under load from the boards it supplies. Normally I would assume a
filter capacitor to be at fault here, but they all check out fine so
something else is causing this ripple. Note there is a characteristic
'knee' on the high peaks and I'm thinking this must be indicative of
*something* trouble is, I don't know what. If anyone recognises this
waveshape and knows what causes it, that'd be "awesome" - as our American
friends describe everything. Check it out:


https://www.flickr.com/photos/128859641@N02/35684682551/in/dateposted-
public/

 

[Cursitor Doom]

On Sun, 09 Jul 2017 10:20:47 -0700, Jeff Liebermann wrote:

Is the mystery load the hardware appearing in adjacent photos? EXIF
says that they were taken 4 days earlier, which suggests a connection.

If the adjacent photos were of any relevance, Jeff, I'd have mentioned it
and linked to them.

Oh, never mind. I found your rather ugly solder wick PCB fix:
https://www.flickr.com/photos/128859641@N02/35602405551/in/photostream/

You might want to double (or triple) check your soldering and PCB
through hole connections.

All I did was replace an electro with one of identical parameters; it
just happened to be a bit smaller than the original (which is not at all
uncommon).

From this photo:
https://www.flickr.com/photos/128859641@N02/35564539582/in/photostream/

there's a tuning screw, semi-rigid coax cable, and cavity filter on the
left side. Too bad the power supply board is missing. There are some
gold connector pins in the photo. So, what is it?

You're complicating this unduly and massively, Jeff. I simply posed a
question about an oscilloscope trace, that's all.

 

[mike]

On 7/9/2017 8:10 AM, Cursitor Doom wrote:

Gentlemen,

The link below shows a scope trace of the output of a linear PSU (voltage
4.7VDC) with about 300mV of 100Hz ripple riding on it. This PSU is in-
circuit under load from the boards it supplies. Normally I would assume a
filter capacitor to be at fault here, but they all check out fine so
something else is causing this ripple. Note there is a characteristic
'knee' on the high peaks and I'm thinking this must be indicative of
*something* trouble is, I don't know what. If anyone recognises this
waveshape and knows what causes it, that'd be "awesome" - as our American
friends describe everything. Check it out:


https://www.flickr.com/photos/128859641@N02/35684682551/in/dateposted-
public/

You might get this when you have two caps separated by an inductor.
First cap usually gets more peak charge current than the second one
and develops high ESR first. Even if both caps are good, the inductor
(or resistor) in between can cause this effect.

 

[Cursitor Doom]

On Sun, 09 Jul 2017 12:34:51 -0700, mike wrote:

You might get this when you have two caps separated by an inductor.
First cap usually gets more peak charge current than the second one and
develops high ESR first. Even if both caps are good, the inductor (or
resistor) in between can cause this effect.

Someone on SER said a non-linear load could explain the shape of that
trace and my initial reaction was that sounded quite plausible. However,
on reflection I think if that *were* the case, then the knee would span
600-700mV (when the semis start conducting) and that isn't what we see
here.
The obvious thing to do next is whip off the output plugs from the PSU
one by one and see if that clears the problem and if so, which sub-
circuit is responsible for the overload as it may be nothing to do with
the PSU at all.

--
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protocols constitutes acceptance of this condition.

 

[Robert Baer]

Cursitor Doom wrote:

Gentlemen,

The link below shows a scope trace of the output of a linear PSU (voltage
4.7VDC) with about 300mV of 100Hz ripple riding on it. This PSU is in-
circuit under load from the boards it supplies. Normally I would assume a
filter capacitor to be at fault here, but they all check out fine so
something else is causing this ripple. Note there is a characteristic
'knee' on the high peaks and I'm thinking this must be indicative of
*something* trouble is, I don't know what. If anyone recognises this
waveshape and knows what causes it, that'd be "awesome" - as our American
friends describe everything. Check it out:


https://www.flickr.com/photos/128859641@N02/35684682551/in/dateposted-
public/

Cause: stored charge in the rectifiers.

 

[David Eather]

On Mon, 10 Jul 2017 01:10:46 +1000, Cursitor Doom <curd@notformail.com>
wrote:

Gentlemen,

The link below shows a scope trace of the output of a linear PSU (voltage
4.7VDC) with about 300mV of 100Hz ripple riding on it. This PSU is in-
circuit under load from the boards it supplies. Normally I would assume a
filter capacitor to be at fault here, but they all check out fine so
something else is causing this ripple. Note there is a characteristic
'knee' on the high peaks and I'm thinking this must be indicative of
*something* trouble is, I don't know what. If anyone recognises this
waveshape and knows what causes it, that'd be "awesome" - as our American
friends describe everything. Check it out:


https://www.flickr.com/photos/128859641@N02/35684682551/in/dateposted-
public/

a soft diode in the bridge rectifier?

--
Using Opera's mail client: http://www.opera.com/mail/

 

[tom]

"David Eather" <eather@tpg.com.au> wrote in message
newsp.y24qvzulwei6gd@fx-6300...

On Mon, 10 Jul 2017 01:10:46 +1000, Cursitor Doom <curd@notformail.com
wrote:

Gentlemen,

The link below shows a scope trace of the output of a linear PSU (voltage
4.7VDC) with about 300mV of 100Hz ripple riding on it. This PSU is in-
circuit under load from the boards it supplies. Normally I would assume a
filter capacitor to be at fault here, but they all check out fine so
something else is causing this ripple. Note there is a characteristic
'knee' on the high peaks and I'm thinking this must be indicative of
*something* trouble is, I don't know what. If anyone recognises this
waveshape and knows what causes it, that'd be "awesome" - as our American
friends describe everything. Check it out:


https://www.flickr.com/photos/128859641@N02/35684682551/in/dateposted-
public/

a soft diode in the bridge rectifier?

--

It is showing two half cycles at 50 Hz and they are the same. Most likely
not a diode issue. Most likely a bad capacitor with high ESR. Or you got the
replacement capacitor in the wrong holes on the pc board. Can you remove the
new cap and get a photo of the top side of the board?

 

[Phil Allison]

Foxs Mercantile wrote:

If anyone recognises this waveshape and knows what causes
it, that'd be "awesome"

Not sure what's causing it, but it's indicative of a non-
linear load. The "knee" is where the load transitions from
one value to a smaller value.

** The "knee" or bump on the saw tooth is caused by electro cap ESR.

If you add a say a 1 ohm resistor in series, the bump will get much larger.

The bump is visible, along with ripple, on most unregulated DC supplies.



..... Phil

 

[Tauno Voipio]

On 9.7.17 23:44, Cursitor Doom wrote:

On Sun, 09 Jul 2017 12:34:51 -0700, mike wrote:

You might get this when you have two caps separated by an inductor.
First cap usually gets more peak charge current than the second one and
develops high ESR first. Even if both caps are good, the inductor (or
resistor) in between can cause this effect.

Someone on SER said a non-linear load could explain the shape of that
trace and my initial reaction was that sounded quite plausible. However,
on reflection I think if that *were* the case, then the knee would span
600-700mV (when the semis start conducting) and that isn't what we see
here.
The obvious thing to do next is whip off the output plugs from the PSU
one by one and see if that clears the problem and if so, which sub-
circuit is responsible for the overload as it may be nothing to do with
the PSU at all.

The peak is definitely from the charge pulse from the rectifier. A
capacitor-input PSU charges only 5 to 10 % of the half-cycle time,
depending on the resistances and inductances in the charge path.

--

-TV

 

[Phil Allison]

Tauno Voipio wrote:

----------------------------------

The peak is definitely from the charge pulse from the rectifier. A
capacitor-input PSU charges only 5 to 10 % of the half-cycle time,
depending on the resistances and inductances in the charge path.

** Wrong on both claims.

The charging current pulse has the same duration as the rising part of the voltage waveform - about 15 to 30% of the half cycle period.

The bump is due to resistance in series with the capacitance - use a film cap and it disappears.




..... Phil

 

[Cursitor Doom]

On Sun, 09 Jul 2017 19:37:39 -0400, tom wrote:
-

It is showing two half cycles at 50 Hz and they are the same. Most
likely not a diode issue. Most likely a bad capacitor with high ESR. Or
you got the replacement capacitor in the wrong holes on the pc board.
Can you remove the new cap and get a photo of the top side of the board?

When I tested this psu out-of-circuit with a dummy load I got less than
5mV of ripple on that rail. Now I may have too lightly-loaded the output,
I can't say for sure, but that does tend to indicate to me I should check
for shorted components down the line from the psu before I do anything
else.

 

[Tom Gardner]

On 09/07/17 16:10, Cursitor Doom wrote:

Gentlemen,

The link below shows a scope trace of the output of a linear PSU (voltage
4.7VDC) with about 300mV of 100Hz ripple riding on it. This PSU is in-
circuit under load from the boards it supplies. Normally I would assume a
filter capacitor to be at fault here, but they all check out fine so
something else is causing this ripple. Note there is a characteristic
'knee' on the high peaks and I'm thinking this must be indicative of
*something* trouble is, I don't know what. If anyone recognises this
waveshape and knows what causes it, that'd be "awesome" - as our American
friends describe everything. Check it out:


https://www.flickr.com/photos/128859641@N02/35684682551/in/dateposted-
public/

It took me <5 minutes to do a spice simulation
sufficient to generate such a picture.

The components were an ideal ac voltage source,
a diode, an ideal capacitor for smoothing, an
ideal resistor for the load, and an ideal resistor
in series with the smoothing capacitor representing
the smoothing cap's ESR.

 

[Phil Allison]

Tom Gardner wrote:

-----------------------

https://www.flickr.com/photos/128859641@N02/35684682551/in/dateposted-
public/

It took me <5 minutes to do a spice simulation
sufficient to generate such a picture.

The components were an ideal ac voltage source,
a diode, an ideal capacitor for smoothing, an
ideal resistor for the load, and an ideal resistor
in series with the smoothing capacitor representing
the smoothing cap's ESR.

** The REAL AC supply is not an good sine wave, it is normally somewhat flat topped. Take a look on a scope using a 10:1 probe.

Transformers have significant resistance in their windings, so you need to add some on the AC side of the simulation. The rising part of the saw tooth wave should not be too short, as it will be with zero source impedance.

If you wish to see reality, forget trying to sim it.

In this case grab any unregulated transformer wall wart, put a resistor across the output and scope the voltage across it.

Takes only seconds and leaves no room for doubt.



..... Phil

 

[Cursitor Doom]

On Mon, 10 Jul 2017 19:06:55 +0100, Tom Gardner wrote:

It took me <5 minutes to do a spice simulation sufficient to generate
such a picture.

The components were an ideal ac voltage source,
a diode, an ideal capacitor for smoothing, an ideal resistor for the
load, and an ideal resistor in series with the smoothing capacitor
representing the smoothing cap's ESR.

You achieved full-wave rectification using just the above parts? May we
see this remarkable circuit, please?

 

[Tom Gardner]

On 11/07/17 19:55, Cursitor Doom wrote:

On Mon, 10 Jul 2017 19:06:55 +0100, Tom Gardner wrote:

It took me <5 minutes to do a spice simulation sufficient to generate
such a picture.

The components were an ideal ac voltage source,
a diode, an ideal capacitor for smoothing, an ideal resistor for the
load, and an ideal resistor in series with the smoothing capacitor
representing the smoothing cap's ESR.

You achieved full-wave rectification using just the above parts? May we
see this remarkable circuit, please?

Half wave rectification is sufficient to show your waveform.

Why do you think full-wave rectification is important? Which
*significant* aspect of your waveform would it change?

 

[Cursitor Doom]

On Tue, 11 Jul 2017 21:11:46 +0100, Tom Gardner wrote:

Half wave rectification is sufficient to show your waveform.

Why do you think full-wave rectification is important? Which
*significant* aspect of your waveform would it change?

I'd KF'd you previously due to your politics, but it seems your
electronics is no better.

<*PLONK!*>

 

[Tim Williams]

"Cursitor Doom" <curd@notformail.com> wrote in message
newsk3e3e$bke$13@dont-email.me...

On Tue, 11 Jul 2017 21:11:46 +0100, Tom Gardner wrote:

Half wave rectification is sufficient to show your waveform.

Why do you think full-wave rectification is important? Which
*significant* aspect of your waveform would it change?

I'd KF'd you previously due to your politics, but it seems your
electronics is no better.

*PLONK!*

For the record, you didn't answer his question. I'm genuinely curious now,
too.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com