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Old 10-05-2014, 12:12 AM
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Tubejunke Tubejunke is offline
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Tektronix 2205 Oscilloscope with flashing trace..

I bought this Tektronix 20Mhz scope to increase my knowledge and capabilities in radio and TV troubleshooting. All of the functions seem to work, but the trace constantly flashes. I have seen videos on YouTube of other scopes and some do the same thing and others have a nice, non strobing waveform.

I'm just wondering if anyone knows about this. Is it normal for some models or is it a defect. It's not actually strobing, but more of a rather large variation in intensity on a steady and constant frequency. It is less disturbing of course if I turn the intensity down low. I am thinking that when there is no signal applied that the flat line is steady.

Any advice here would be greatly appreciated
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Old 10-06-2014, 09:33 AM
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Make sure the sweep mode isn't in chop or alternate - both will give a strobed effect to the sweep. At slower sweep speeds, this effect is quite noticeable.

I generally use auto sweep, one channel, and trigger on that channel. I rarely use more than one channel when using my scope (with 5 channels!).

Hope this helps,
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Old 10-07-2014, 04:33 PM
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OK Brian, I will check my settings. Also, I need to find two cables for my scope. One would be BNC to BNC to run from my function generator to the scope. Another would be a BNC with alligator clip ends to apply signals from the generator to a circuit. Not that my lack of having these is the problem.

Just figured I would mention it because I was using an O scope probe to apply and/or measure signals from the generator until I found out that evidentally all scope probes are made with resistance wire. Someone on another page mentioned a need for the same thing as I and they thought that they could just cut the probe off and add some clips. Not quite that simple.....
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Old 10-07-2014, 09:01 PM
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If you have the trigger level set near zero, random noise will trigger the sweep intermittently. If you turn the trigger level up or down, two things can happen:
1) sweep stops completely (trigger not on auto)
2) sweep becomes steady (trigger on auto)
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Old 10-08-2014, 01:55 AM
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Quote:
Originally Posted by Tubejunke View Post
I am thinking that when there is no signal applied that the flat line is steady. Any advice here would be greatly appreciated
Wow! I've never quoted myself before.. Anyway, with the two sets of possibilities that I have so far been given I had time to check things out. First off I realized that I was wrong in saying the above first sentence. It does this at all times; signal applied or not.

I tried everything mentioned thus far and every other combination of the many (too many) settings and nothing will give me that rock steady trace that I would like to have and have seen on even the oldest of units. Again though I have seen others that do the same thing in YouTube vids, but the videos I have seen it in are not about this particular issue.

All in all I like this scope. Once the college loaned me one of their digital pieces of junk in my opinion and I quickly realized why my professor had the labs set up with analog scopes. Admittedly, I know that digital units have come a long way and I would hope so as much money as can be spent on one. I guess there is at least one good reason why I am not an engineer which would be about the only reason I think that you would need the numbers and capabilites of the new generation of scopes.

They say there are a few odd ball guys in the upper echelons of electronics that still use older analog equipment, but supposedly they get a lot of ribbing from their peers. Sort of like me taking my Simpson 260 to work and getting 'the look', even from my boss who I went to school with. Funniest thing is one day we had a piece of equipment with a bad potentiometer. The house Fluke 5 had some issue besides the mind boggling array of way too fast moving numbers.

So it was Simpson to the rescue. Of course I was the only tech there who could operate it. My boss tried to brush off the embarrassment of not being the superior being my telling me that it was too old and could only measure 10Kohms (the highest selection) and we had a larger pot. I tried to explain multipliers, but time has moved forward too far I guess. People now just want everything simple, easy and basically done for them without thought. I did at least get to prove the undeniable tool that the analog meter is in this particular instance by showing them the sweep of the dial indicator up to the problem point within the potentiometer.

I better stop before I go on another rant about the dumbing down of electronics. In a sentence at least, you simply don't need to know what you used to.....
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Old 10-08-2014, 03:53 AM
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Quote:
Originally Posted by Tubejunke View Post
I tried everything mentioned thus far and every other combination of the many (too many) settings and nothing will give me that rock steady trace that I would like to have and have seen on even the oldest of units. Again though I have seen others that do the same thing in YouTube vids, but the videos I have seen it in are not about this particular issue.:
Setting up, I'd choose:

Working, left to right, choose channel 1, norm, alt, mid-to-fast sweep speed (1msec/div or faster), trigger centered (slope switch to either setting for now), sweep mode to PP-Auto, source to channel 1 or vert mode.


Quote:
Originally Posted by Tubejunke View Post
They say there are a few odd ball guys in the upper echelons of electronics that still use older analog equipment, but supposedly they get a lot of ribbing from their peers. :
Jim Williams, a famous IC designer for both National Semiconductor and Linear Technology, once wrote about his home lab, which consisted of all analog equipment. His book "The Art and Science of Analog Design" had a chapter about his home lab, with a picture of it, and not one piece of digital equipment is to be found. Far from oddball, old-school, or antiquated, and he was esteemed by everyone!

Cheers,
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Old 10-08-2014, 06:09 PM
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OK Brian, thanks again. I am not home with the scope at the moment, but will try what you mentioned as soon as possible. That story about Jim Williams is quite refreshing. Sometimes I feel as if my 'analog' ways will leave me behind in the electronics world, or more specifically; on the job.

I guess it's really a matter of what facet of electronics you are involved with and/or interested in. I find low voltage semiconductor, microchip stuff to be a bore personally, but I must accept and understand it to a certain degree to be any kind of a tech these days. I really wish that I lived near one of the music amplifier companies that still produce vacuum tube equipment, or even some service center for that matter. It just doesn't exist anywhere near my home here in VA. It would be great though even to be involved in the production of that equipment.

There should still be some home audio companies producing tube amplifiers. I know that big component stereo equipment like so many things is suffering a decline in interest due I guess to the Ipods and smart?phones.
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Old 10-09-2014, 06:16 AM
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Quote:
Originally Posted by Tubejunke View Post
Sometimes I feel as if my 'analog' ways will leave me behind in the electronics world, or more specifically; on the job.
I too am an analog junkie - my only digital preferences are in frequency counters and some high accuracy DMM applications. I was a child of the 70s/80s and was never impressed by all the "digital" innovations.

Quote:
Originally Posted by Tubejunke View Post
I really wish that I lived near one of the music amplifier companies that still produce vacuum tube equipment, or even some service center for that matter. It just doesn't exist anywhere near my home here in VA. It would be great though even to be involved in the production of that equipment.

There should still be some home audio companies producing tube amplifiers. I know that big component stereo equipment like so many things is suffering a decline in interest due I guess to the Ipods and smart?phones.
The problem with companies wishing to make tube audio equipment these days is the audiophiles - they either trash it if it can be produced cheap or praise it, creating demand, and driving the price beyond what most can afford. I was given a Daisano tube preamp, made in Japan in the early 90s, that was about 120 bucks new. One bad audio review, and the company folded, creating an orphan, that then was worth quite a lot due to it's rarity. Once I got a Magnavox tube amp, I sold the Daisano on eBay, and got almost 700 dollars from an audiophile lawyer in Connecticut. One tranny, two 12AX7s, and a few other parts....for 700 bucks? Clones of the Daisano now come from China, with iPod connectors for about 270 bucks. There are even more preamp kits than finished products, all overpriced.

Cheers,
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  #9  
Old 10-12-2014, 03:35 PM
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Quote:
l I found out that evidentally all scope probes are made with resistance wire. Someone on another page mentioned a need for the same thing as I and they thought that they could just cut the probe off and add some clips. Not quite that simple.....
Actually, the wire is just wire. The "probe" as a finished item, has an impedance
matching item on it, and includes a trim cap that you make sure the little test
wave looks square when tested. It's on the front of that scope, 1khz test I think it says...
1khz at something like .5v...

if the probe has also a 10X divider built in, you will have a switch that will divide your
signal source by 10. 100v signal will max at 10v. I use to use home made probes with
rg6 and connectors from RS, just be careful where you stick it, you don't wanna
overload the vertical amplifiers in the scope. AND most important, check to be sure
your potential between ground for the scope, and ground on yer test item is 0V.
Be aware Hot chassis sets can make cool sparks shows if you ground a ground
to a not so ground ground.

Also check the sensitivity of the brightness control, it may be noisy and flash the
screen. But mostly as mentioned, the sync will flash the screen if it's not
running freely enough. If you hook up your ch1 to the test point, and sync
off ch1 as well, you should see a stable square wave, and the sync should lock,
and you should be able to get a stable screen... turn the variable sync threshold
you should see it lock at one end, and maybe even stop scanning,
and lose sync at the other extreme...

.
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Last edited by Username1; 10-12-2014 at 03:44 PM.
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Old 10-13-2014, 07:14 PM
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I copied this from the other thread that I made that can be found in Vintage Test Equipment. I think I titled it WTB Two Sets of Leads. At any rate a good fellow who calls himself NoPegs posted this and the link to a YouTube video that explains what I was trying to say. And yeah, I'll watch out for a ground loop. Your mention of transformerless "hot" chassis leads me to something that I have wondered for a while, but never posted anything about. What is the approach to using a scope or even other test equipment with a "hot" chassis? I'm sure it's simple and I will fell dumb when I hear the answer. Would an isolation transformer be the right way to go?

So anyway, here goes with what NoPegs said and that link: "The old scope probe is a no-go my friend. In short, they're not built with normal coax. For more detail you can watch https://www.youtube.com/watch?v=OiAmER1OJh4"
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Old 10-13-2014, 07:41 PM
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Quote:
Originally Posted by Tubejunke View Post
...What is the approach to using a scope or even other test equipment with a "hot" chassis?... Would an isolation transformer be the right way to go?...
Definitely! Plug the TV into the isolation transformer. Then when you connect the scope ground to the chassis, it establishes that the chassis is at ground potential. If you don't use an isolation transformer, you may have the chassis hot, which is both a shock hazard and an arc hazard.

The scope will have a three prong grounded plug. Use it with a correctly wired three prong grounded electrical outlet and do not try to defeat it in any way. If you trip a breaker or GFI socket, it is evidence that something is dangerously wrong with your setup.
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Old 10-14-2014, 01:32 AM
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Quote:
Tubejunke OK Brian, I will check my settings. Also, I need to find two cables for my scope. One would be BNC to BNC to run from my function generator to the scope. Another would be a BNC with alligator clip ends to apply signals from the generator to a circuit. Not that my lack of having these is the problem.
Another link to one of Dave's great videos. This one explains why is may not be a good idea to just assume that a piece of coaxial cable will function correctly in all situations when used with an oscilloscope.

Of course it depends on the application.


The measurements made with an oscilloscope are only as good as the oscilloscope and the probes that are used.

I am posting a clickable link to Tubejunke's information just to make it easy because it is some great information for those that are interested.
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