EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: opensourcefan on January 23, 2016, 12:25:46 am
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Hello, I'm new to the forum and new to electronic engineering. I think I'm having a bit of an issue with my V-222 scope and I have searched but I don't really know what to call my issue so that didn't go well.
This scope was purchased used on eBay and has always performed like this.
I can't get any wave forms to show completely. To identify the wave form ie. a triangle wave, I need to slow the Time/Div to a moving dot, then I can see it's moving in a triangle pattern but of course it's only a dot that I'm seeing. If I speed up the Time/Div the triangle wave flattens out. This is true for a square wave as well, I only get the top and bottom and the faster the Time/Div the flatter it gets and ends up just being oscillating up down flat lines. Everything eventually goes to a flat line. Is this normal for an old analog 20MHZ scope?
This happens on both channels. I have taken the unit apart and it is very clean with no damage. I found a large input filter cap with cold broken joints so I removed it, checked it and re-installed it but no change. No other caps appear to be bulging, leaking or bad. I can't see anything obvious that may have released smoke.
If this isn't normal and something is broke I would greatly appreciate some hints as to what this issue would be called so I can know where to start looking. I do have the manual with schematics. If there is any obvious info that I missed to help with this please advise.
Thank you.
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Welcome to the forum.
Pics of the probe cal waveform will help.
So we're all on the same page ;) link to Service manual:
http://elektrotanya.com/hitachi_v211_v212_v222_v422_sm.pdf/download.html (http://elektrotanya.com/hitachi_v211_v212_v222_v422_sm.pdf/download.html)
Note this site checks to see if you have downloaded more than 2 free manuals/day then offers a link.
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Thank you for the welcome.
I made a quick video: It is a triangle wave from a 555 astable circuit. I start out at the lowest Time/Div and gradually increase it to max, then back down again.
https://youtu.be/pulFD-4gcPo
Hope this helps some.
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Seems to be a low frequency input signal, try a faster one for triangle goodness ;)
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Ah yes, it is a very low freq signal indeed, just an led flashing on and off (300ms). This was my first kick at the kitty with this setup, I should have known better.
Thank you.
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No problem, enjoy the scope. Played around with one, seems like a fine piece of kit ;)
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The vid did not reveal much. :-//
So I'll ask again for Pics of the probe cal 1 KHz waveform.
Simple pic is all that's required and NOT in the dark and preferably of the whole front of the scope.
Use the "Attachments" and upload a photo.
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"probe cal 1 KHz waveform" I'm just guessing but is this what you mean?
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"probe cal 1 KHz waveform" I'm just guessing but is this what you mean?
Exactly.
Every scope has one and it's the first thing you use for a "sanity" check.
Looks perfect with a nice sharp trace. :-+
Back to the original problem; a CRO struggles to display slow frequency waveforms in a manner that is obvious to the inexperienced....but you've leant that. ;)
Enjoy.
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Thank you for the welcome.
I made a quick video: It is a triangle wave from a 555 astable circuit. I start out at the lowest Time/Div and gradually increase it to max, then back down again.
(video here)
Hope this helps some.
This looks 100 percent totally normal to me.
You are scoping a very low frequency signal, and since you aren't using a DSO, the dot does not leave a "trace" behind it, except that due to the persistence of the phosphor. As you make the horizontal timebase faster and faster, the scan of the beam increases until you see what looks like a single continuous trace across the entire screen. It is still moving up and down at the frequency of the input signal, very slowly compared to the horizontal scan rate.
Here's the same thing shown on my Tek 2213a. It has a slightly more persistent phosphor than your V-222.
https://www.youtube.com/watch?v=EOYDzt08RD0 (https://www.youtube.com/watch?v=EOYDzt08RD0)
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Thank you very much for the confirmation, that does behave exactly like mine.
I'm slowly learning :o
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You are very welcome.
And thank you, for this opportunity to illustrate another important difference between analog and digital oscilloscopes. While there are several very good low-end DSOs on the market which tempt beginner scoposcopists, I still maintain that it is better to learn the basics on an analog scope. You should understand the relationship between scan rate, graticule markings and signal frequency in the time domain, and between displayed signal amplitude, channel input attenuation settings and graticule markers in the voltage domain, so that you can read frequencies and voltages from the screen display without depending on the (digital) scope's "numbers in boxes".
DSOs make it way too tempting to bypass this knowledge base. You can just press the "Auto" button and select some Measurements, and you don't even need to look at the waveform itself..... but you should do. One should always check the "numbers in boxes" against what the trace is _actually_ showing you, using the horizontal and vertical settings and the graticule markings.
Using an analog scope as one's first scope rather forces one to develop these skills from the very beginning. Then when one transitions to the DSO, one not only has a better appreciation for its "bells and whistles" but also one has the basic knowledge to avoid being fooled by what it is showing and telling you.
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Using an analog scope as one's first scope rather forces one to develop these skills from the very beginning. Then when one transitions to the DSO, one not only has a better appreciation for its "bells and whistles" but also one has the basic knowledge to avoid being fooled by what it is showing and telling you.
+1
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I decided to play around a bit more and built a little F-Gen out of a XR2206. I'm happy to report that all is well with this scope now that I have some higher frequency's hitting it.
Just need to un-stick the Ch2 Volts/Div knob, wow is it stiff, almost need a pair of pliers.
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Nice looking traces you got there! Cool little scope.
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Love those channel coupling switches, I'd flip em just for the sensation :D
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That actually is a decent little scope, it was my first "real" / modern scope and had a real workout with tube amps. Sadly, it developed a triggering problem along with channel 1 controls becoming worn / dirty and the scope was just problematic. Now it has been relegated to the corner of the room.... Someday, someday, maybe I'll find the time to look at it - which is doubtful.
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If anyone has any advice on how to clean those strange white pots on the inside that would be cool. I was going to hit them with contact cleaner hoping that some would work it's way into the housings. I did find a thread regarding this but no real solution.
I do love this scope though, as my first it feels great and exudes quality.