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Author Topic: Oscilloscope training class (long)  (Read 92422 times)

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Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #25 on: September 11, 2011, 11:51:09 AM »
Do I understand it correctly that this is what Agilent's MegaZoom technology is for?

I remember Megazoom as a memory management technology from Agilent's digital scopes from about a decade ago, like the 54600 series - to make it easy to navigate through deep record memory.  Of course, back then, 1Mpoints was considered deep memory.  Are they still using this Megazoom terminology today?
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Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #26 on: September 11, 2011, 11:53:09 AM »
Just last night I was trying to find information about 1x vs 10x probes, ac vs dc coupling, and triggering. I found your channel and it was exactly what I was looking for! Great videos with great explanations! Thanks!

Joshua,
I'm glad you found the videos useful!  It's a good thing I did three videos specifically on those topics!!  Of course, please let me know if there are other similar topics that you'd like to see in the future.

Best Regards,
Alan
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Offline ToBeFrank

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Re: Oscilloscope training class (long)
« Reply #27 on: September 12, 2011, 02:10:54 AM »
Do I understand it correctly that this is what Agilent's MegaZoom technology is for?

I remember Megazoom as a memory management technology from Agilent's digital scopes from about a decade ago, like the 54600 series - to make it easy to navigate through deep record memory.  Of course, back then, 1Mpoints was considered deep memory.  Are they still using this Megazoom terminology today?

Yes, they are. I was really confused by your video. I couldn't figure out why your scope didn't always use all its acquisition memory. After some searching, I think this is because my scope has the MegaZoom feature. If I understand it correctly, MegaZoom allows them to always fill memory at max possible sample rate without affecting update rates. Thus, MegaZoom equipped scopes don't have a record length selection.
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #28 on: September 12, 2011, 06:03:47 AM »
Yes, they are. I was really confused by your video. I couldn't figure out why your scope didn't always use all its acquisition memory. After some searching, I think this is because my scope has the MegaZoom feature. If I understand it correctly, MegaZoom allows them to always fill memory at max possible sample rate without affecting update rates. Thus, MegaZoom equipped scopes don't have a record length selection.

Ok, very good, I didn't know that about the MegaZoom.  I assume that this means that you'd be able to make an accurate measurement (like a frequency measurement) on these two signals simultaneously, even though their frequencies differ by 10,000.  I know that some of the older scopes made the measurements on the displayed points, and not on the complete max-sample rate points, which would result in errors in the frequency measurement for the higher frequency signals when time/div was adjusted for the lower frequency signal.  Has this been addressed in the newer incarnations of MegaZoom?  What scope do you have?
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Offline ToBeFrank

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Re: Oscilloscope training class (long)
« Reply #29 on: September 12, 2011, 08:50:27 AM »
I know that some of the older scopes made the measurements on the displayed points, and not on the complete max-sample rate points, which would result in errors in the frequency measurement for the higher frequency signals when time/div was adjusted for the lower frequency signal.  Has this been addressed in the newer incarnations of MegaZoom?  What scope do you have?

That's still the same on my DSOX3000 scope. You zoom in on the higher frequency signal to make the measurements.
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #30 on: September 12, 2011, 09:18:59 AM »
That's still the same on my DSOX3000 scope. You zoom in on the higher frequency signal to make the measurements.

Oh, OK.  I guess that's part of why the scope feels fast, because it's making its measurements on the decimated data points rather than the full set of samples.  Does it give you any indication that the displayed result may be inaccurate due to the sample decimation?
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Offline Snapcase

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Re: Oscilloscope training class (long)
« Reply #31 on: September 29, 2011, 08:42:55 PM »
This is awesome. Thanks so much!

I've got a Tektronix 2225 for cheap some time ago. But I've never learned how to use it quite well. I decided to fully go over it along this week and finally fully learn how to get the most of it. I've made some searches and found Dave's #196 video. That was a great start. He fully describes the 2225! Never heard of the EEV blog before, watched a couple of dozens of his videos and went very curious about the forum. Just joined a few minutes ago (my very first post here) and just found this. Amazing! it's been a very fruitful week!

Thanks so much, guys. You both made my day!
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #32 on: October 02, 2011, 01:06:33 PM »
This is awesome. Thanks so much!

I've got a Tektronix 2225 for cheap some time ago. But I've never learned how to use it quite well. I decided to fully go over it along this week and finally fully learn how to get the most of it. I've made some searches and found Dave's #196 video. That was a great start. He fully describes the 2225! Never heard of the EEV blog before, watched a couple of dozens of his videos and went very curious about the forum. Just joined a few minutes ago (my very first post here) and just found this. Amazing! it's been a very fruitful week!

Thanks so much, guys. You both made my day!

Congrats on the 2225!  Be sure to ask if you have any questions.  If the loooooong "Scopes for Dopes" class video doesn't answer your questions, or any of the dozen or more videos on my youtube channel http://www.youtube.com/w2aew don't help, be sure to ask - we'll be happy to help you out.
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Online EEVblog

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Re: Oscilloscope training class (long)
« Reply #33 on: October 15, 2011, 02:48:18 PM »
To make it easier to navigate this long video - over 2 hours long, here is a list of time-stamps and the topics that begin at those timestamps. Using this "table of contents", you can easily move the youtube player location to the topic of interest.

0:00:00 Opening and Agenda
0:02:50 Brief History of Oscilloscopes – with Al Klase
0:15:00 Start of Basics of Oscilloscopes – with Alan Wolke
0:19:00 Basic Block Diagram of an Oscilloscope
0:19:50 Oscilloscope / Display Overview
0:23:00 Display Section Functions and Controls
0:28:10 Vertical Section Description
0:33:17 Vertical Scale / Coupling Controls, Input Impedance
0:38:04 Vertical Mode Controls
0:48:05 In-circuit Example of using two traces on the oscilloscope
0:52:41 Horizontal Section Description
0:53:48 Horizontal Sweep Types & Controls
1:10:15 Triggering (Synchronization) Section Description
1:13:19 Trigger Source, Mode and Coupling Controls
1:19:56 Trigger Level and Slope Controls
1:23:29 Introduction to Oscilloscope Probes
1:31:45 1X and 10X Passive Probes
1:34:00 10X Probe Compensation and Use Considerations
1:48:48 XY Mode of Operation
2:00:12 Front Panel Control Layout
2:02:20 Pop Quiz!
2:03:00 Wrap Up: Oscilloscope adds Intuitive Feel to circuit operation
2:04:45 Questions and Answers
2:13:35 Brief History of Oscilloscope Tubes

Awesome work.
People always keep asking me for a "simple" and "short" beginner oscilloscope tutorial, it's just not possible, there is just so much stuff to cover. I'm surprised you got it all into in a 2 hour presentation!

Dave.
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #34 on: October 22, 2011, 12:10:27 PM »

Awesome work.
People always keep asking me for a "simple" and "short" beginner oscilloscope tutorial, it's just not possible, there is just so much stuff to cover. I'm surprised you got it all into in a 2 hour presentation!


Thanks Dave.  Of course, this only covers the basics of the old school analog scopes.  Lots more to cover on these (advanced triggering, delaying timebases, etc.), so I've tried to cover those with some of my other vids. 

Then there's a whole host of additional topics when you get into digitizing scopes, with issues such as sample rate, aliasing, memory length, automatic measurements, etc.  It hit me one day when speaking with a younger colleague about a scope, and I said something like "...now change the sweep speed...", and he stopped me and said, "What's a sweep speed?"  All he had ever seen was a Horizontal Scale control on a digital scope.  Sad.  I hate to see the genius and power of the analog scopes fade away.
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Offline Mint.

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Re: Oscilloscope training class (long)
« Reply #35 on: November 19, 2011, 12:01:45 PM »
Excellent class, however, the sound quality was very poor and hard to understand. You gotta focus real hard to hear what they say  >:(
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Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #36 on: November 19, 2011, 02:22:54 PM »
Excellent class, however, the sound quality was very poor and hard to understand. You gotta focus real hard to hear what they say  >:(

I'm sorry about the audio quality.  Unfortunately, the decision to record the class was a "last minute" decision, and thus the right equipment and setup wasn't available.  Originally, I was just going to teach the class to the group in attendance only.  I'm glad that it was recorded, but you are right, the audio isn't great.

So, if you have any questions on what was said - just ask me!  I should remember what I said... ;-)
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Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #37 on: January 07, 2012, 12:40:30 AM »
...reposted here by request...

A question I'm often asked is - how much BW do I need get with my oscilloscope.  I usually answer with - get as much as you can afford!  Even low frequency circuits can do some wacky high frequency things.  Check out my latest video for an example...
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Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #38 on: January 30, 2012, 08:37:19 AM »
I posted another video (by request).  This on describes the function and use of some of the Vertical controls on an analog scope - specifically the ALT, CHOP, ADD and INVERT functions.
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Offline Chris Wilson

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Re: Oscilloscope training class (long)
« Reply #39 on: February 02, 2012, 07:37:30 AM »
I believe that if an independent like yourself did a short video on choosing a `scope for automotive (engine analysis) work it would be both popular and very useful. All the ones I have found save a few by ScannerDanner on YouTube, have been by people trying to sell you their product, and I have found them couched in tech speak that hides the products weaknesses whilst extolling their (fantastic) strengths ;) Memeory depth and the ability to run a slow timebase seem essentials, but how would an analogue `scope fare, is it essential to go digital? One maker of specialist USB `scopes for automotive use says their floating inputs are essential, another very popular maker poo poos this and says it's not necessary, then a month later, on their own forum, goes into a diatribe of the risks of injudicious probing.
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Offline sdscotto

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Re: Oscilloscope training class (long)
« Reply #40 on: February 12, 2012, 09:43:06 AM »
I've added a number of new videos to my YouTube channel regarding oscilloscope usage.  The two most recent additions illustrate how to properly simultaneously capture and visualize two signals that are at dramatically different frequencies.

Thanks for doing these series of tutorial videos.

I have always struggled with the delayed timebase feature on my analog scopes.  I followed along in your tutorial with both a 2252 and 2232 (in analog mode), and learned that my most basic mistake was incorrectly triggering on the B sweep.

However, I found that the B trace was almost invisible at 50ns, even with max brightness/contrast.  At first I thought it was because of the age of my scopes and the possibility that the CRT was not as bright as it could be, but in reality, they are extremely bright.

Is it normal for the B sweep to be so low in contrast well within the bandwidth of the scope?  Are there certain analog scopes that are better than others for displaying delayed timebase?

Thanks in advance!
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #41 on: February 12, 2012, 12:57:29 PM »
Thanks for doing these series of tutorial videos.

I have always struggled with the delayed timebase feature on my analog scopes.  I followed along in your tutorial with both a 2252 and 2232 (in analog mode), and learned that my most basic mistake was incorrectly triggering on the B sweep.

However, I found that the B trace was almost invisible at 50ns, even with max brightness/contrast.  At first I thought it was because of the age of my scopes and the possibility that the CRT was not as bright as it could be, but in reality, they are extremely bright.

Is it normal for the B sweep to be so low in contrast well within the bandwidth of the scope?  Are there certain analog scopes that are better than others for displaying delayed timebase?

Thanks in advance!

The low brightness of the B sweep is most likely normal - it depends a lot on the difference between the sweep speeds of the A and B sweeps.  The larger the difference, the dimmer the B sweep will be.  Some scopes (like the 485) had a separate intensity control to help brighten up the B sweep when using high levels of "zoom" in the sweep speeds between A and B. 

A few "special" models of scopes, like the 2467, included a very special CRT - something called a Micro-channel Plate CRT.  This CRT had an electron multiplier immediately behind the CRT's face which dramatically improved the writing rate - and thus the brightness of these very fast sweeps. I show this scope in a few of the videos, like the one that shows the characterization of the RF Power Detector.

For most scopes - yours included that do not have have these special features, the intensity of the B sweep can be improved by using a smaller ratio of A:B sweep speeds when possible.  Or simply change the Horizontal Mode from ALT (alternating between A and B) to using just B only.  In other words, use ALT-A/B to properly set the delay and B sweep speed.  Then, once they're set, change the horizontal mode to B-only to just show the B sweep.
« Last Edit: February 12, 2012, 12:59:21 PM by w2aew »
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Offline Chris Wilson

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Re: Oscilloscope training class (long)
« Reply #42 on: February 13, 2012, 06:40:52 AM »
I think I can guess the answer, but why have most CRT type analogue and digital scopes historically had relatively tiny screens compared to say a TV? Is it something to do with cost of tube manufacture that is either accurate enough, or trace refresh fast enough, in large sizes that is / was the limiting factor? I know some of the automotive engine analysers from the likes of Sun had TV sized screens, but i guess they are being used at low refresh rates? Where there any relatively fast scopes ever made with large screen sizes? Just curious.

I am also curious as to why analogue scopes have vast amounts of set up "adjusters" inside them for calibration purposes, yet even a high end USB scope has virtually nothing obviously adjustable within them.

Great video re triggering again, the last one on auto triggering. I thank you for these.
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Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #43 on: February 13, 2012, 07:54:43 AM »
Chris - as you guessed, it all comes down to speed.  TV screens are scanned at much slower rates than even a modest analog scope.  The lower scan rates allow for magnetic deflection (coils on the outside of the neck of the tube), which would generally be incompatible with fast deflection speeds.  CRTs in analog scopes used electrostatic deflection (deflection plates inside neck of the tube), which lend themselves to much faster drive frequencies.

As for calibration adjustments in the analog scopes...  There are a lot of variables that enter into the accuracy of the analog scopes, mainly due to the multitude of circuitry between the front panel connector and the deflection plates (attenuators, preamps, amplifiers, offset control circuits, drivers, final amps for the plates, etc. - and that's just a portion of the vertical analog path).  Each of the analog circuits will have offsets, non-linearities, etc. that need to be zero'd out to calibrate the response).  Similar adjustments would be need for the horizontal and trigger circuits.

By contrast, the digital scopes are much simpler.  There is some analog conditioning circuitry between the front panel connection and the ADC (analog to digital converter).  Once the signal is sampled by the ADC, any calibrations adjustments to the signal can be applied digitally before being displayed.  Thus, ALL of the complexity of amplifying the signal to drive the deflection plates of the scope is gone.  Basically all of the calibrations and corrections are applied to the sampled data numerically after the data is sampled using calibration data installed at the factory. 
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Offline jahonen

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Re: Oscilloscope training class (long)
« Reply #44 on: February 13, 2012, 11:47:03 PM »
I think that the analog CRT could be bigger with an electrostatic deflection without any sacrifice of a speed, but deflection angle of an electrostatic deflection system is usually small. Correction of non-linearities resulting from larger angle becomes more difficult considering faster sweeps.

That means if the scope screen would be bigger (keeping the deflection angle constant), then the CRT neck would become impractically long (it is already very long even with "small" scope screens). Scale that length in proportion of your desired screen size and think whether or not you would want it to your bench. TV CRT's used 90 or 110° deflection angle, thus it makes shorter tube necks possible.

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Janne
 

Offline Chris Wilson

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Re: Oscilloscope training class (long)
« Reply #45 on: February 14, 2012, 12:28:13 AM »
I think that the analog CRT could be bigger with an electrostatic deflection without any sacrifice of a speed, but deflection angle of an electrostatic deflection system is usually small. Correction of non-linearities resulting from larger angle becomes more difficult considering faster sweeps. <SNIP>

http://www.ebay.co.uk/itm/OSCILLOSCOPE-COUNTER-TIMER-MULTIMETER-TEKTRONIX-2236-/150757466948?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2319d86344

He obviously doesn't know this ;)

Thanks for another detailed and helpful reply, I have to say one of the nice things about my USB scope is I can be working on a vehicle and have the 17 inch laptop display show the traces, or even a 24 inch monitor or one could use a projected image. It's a big time saver being able to watch traces without coming out of the footwell, or walking upp to a tiny screen.
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Offline tekfan

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Re: Oscilloscope training class (long)
« Reply #46 on: February 14, 2012, 01:41:38 AM »
Somewhere I read a story about Tektronix. Sometime in the late 80's they were designing transient digitizers that used a scan converter tube. They made digitizers that could capture 4 GHz transients. The russians then invited the guys from Tek to show them their transient digitizer. While the Tek digitizer fit into a 19'' rack the russian version had a scan converter tube that was 10 feet long and worked well into the 20 GHz range.



Quote
This tube is very similar to the Tektronix T-7912 scan converter CRT, which was capable of recording 2.5 gigahertz signals. A 'write' electron gun with traveling wave deflection system deposits charge patterns on a thin silicon wafer. These patterns are read by a low velocity 'read' electron beam from a gun mounted in the opposite end of the tube, scanning the back surface of the silicon wafer.
[From Peter A. Keller, The Cathode-Ray Tube, Palisades Press, 1991]
Total length : 57.5 cm (22.64 in)

A nice site for old tubes: http://www.lampes-et-tubes.info/p/sc.htm
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Re: Oscilloscope training class (long)
« Reply #47 on: February 14, 2012, 05:55:42 AM »
I think that the analog CRT could be bigger with an electrostatic deflection without any sacrifice of a speed, but deflection angle of an electrostatic deflection system is usually small. Correction of non-linearities resulting from larger angle becomes more difficult considering faster sweeps.
The voltage swing was also limited by the output transistors avaliable at that time. You may be able to do something about the plate geometry to increase deflection, but I'm not sure if this can be done without any reduction in bandwidth.

That means if the scope screen would be bigger (keeping the deflection angle constant), then the CRT neck would become impractically long (it is already very long even with "small" scope screens). Scale that length in proportion of your desired screen size and think whether or not you would want it to your bench. TV CRT's used 90 or 110° deflection angle, thus it makes shorter tube necks possible.
There's definitely a correlation between deflection angle and bandwidth. For example the 1 GHz Tektronix 519 (ca. 1959 or so, the input directly drove the vertical plates, without any amplifications/attenuation) had a very small CRT surface, only 4x2 divs or so. The low-bandwith Tektronix 5000 series, designed for biomedical experiments, had a very large CRT. Bandwidth was ultimately limited by the depth of a standard 19" rack as used by the US army (how many people do atomic bomb tests in their backyard?). I believe the USSR had a scope with a larger bandwidth, which just used an extremely long CRT. No idea if this idea ever made it into production.
 

Offline WBB

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Re: Oscilloscope training class (long)
« Reply #48 on: March 14, 2012, 08:19:53 AM »
Thanks for the excellent videos. They have been very educational, easy to follow & understand. Excellent work that is very much appreciated.

A few questions about the coax video. Would other faults show up? eg, a hole in the shield but not a complete break? A compressed shield but not touching the center conductor and creating a short, yet? Also, is it possible to calculate the distance to a short?

Sorry for all the questions. All your videos have been great but the coax one is a subject that I am specifically interested in! Again, thanks for the great work.
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #49 on: March 14, 2012, 08:56:31 AM »
Thanks for the excellent videos. They have been very educational, easy to follow & understand. Excellent work that is very much appreciated.

A few questions about the coax video. Would other faults show up? eg, a hole in the shield but not a complete break? A compressed shield but not touching the center conductor and creating a short, yet? Also, is it possible to calculate the distance to a short?

Sorry for all the questions. All your videos have been great but the coax one is a subject that I am specifically interested in! Again, thanks for the great work.

The answer is - it depends....

- a hole in the shield without a complete break, or a compressed shield may or may not show up.  It all depends on how much of an impedance discontinuity it creates.  Impedance discontinuities cause reflections, just like the mis-termination of the end of the line (like the open circuit example I used, or the shorted example I showed).  The worse the impedance discontinuity of the defect, the easier it will be to detect.  Once observed, you can measure the round-trip delay and calculate the approximate position of the defect.

- Yes, you can determine the distance to a short (only the first short!).  You can see this at the end of the video where I dialed the pot down to zero.  You can measure the width of the pulse that's shown, and that will be the roundtrip delay from the scope to the short and back.  Calculate the distance the same way as I did for the open.

For those that missed it, here is the video that WBB is referring to:
« Last Edit: March 14, 2012, 08:59:22 AM by w2aew »
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