Problem with oscilliscope

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David Kunkle
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Problem with oscilliscope

Post by David Kunkle » Wed Sep 21, 2016 7:26 pm

Bought my first oscilloscope off ebay for $35. Phillips PM 3200. Excellent condition- especially for as old as it must be. Figured out 90% of it so far by playing with it and a 9V battery. Have a manual coming that I bought separately.

Problem is that on the CRT screen, it has just a dot that moves. It leaves no "trace" behind like a sine wave, etc. that I'm used to seeing in pics and video. Is this some ancient scope that will not do this, something set wrong, or something burned out? It will be a pain to take measurements with just a dot jumping around. Thanks for any help.
If your experiment needs statistics, you ought to have done a better experiment.

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Rex Allers
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Re: Problem with oscilliscope

Post by Rex Allers » Wed Sep 21, 2016 10:20 pm

Searching ebay for PM3200 and closed listings, I found this picture, maybe the one you bought.
PM3200.jpg
Sorry to be the bearer of bad news, but that's a pretty crappy scope even if it works perfectly. Only one channel, and only 10 MHz bandwidth. I think most people would recommend a useful scope should have at least two channels and 100 MHz bandwidth or more.

Anyway, to your actual question. Set the sweep timebase (TIME/div) somewhere around the middle, like in the picture. Set X DEFL (x deflection) to INT (internal). External should move the dot left/right as a voltage is applied to the X Input. This is usually called X/Y mode. In Internal, the dot should be swept from left to right at the rate determined by the timebase.

The trace (dot left-right drive) normally won't start until triggered. You should be able to get it "free running" by setting the right-hand triggering switch to LINE. This should start the trace at the AC line rate (50 or 60 Hz). If you set the sweep rate very low (CCW end of the dial) you should be able to see the dot sweep left to right at a slow rate. As the sweep rate is raised the human eye (and phosphor persistance) should just see a horizontal line.

Most scopes have a square wave output. You can connect a probe from the input of the scope to this terminal and see a square wave on the display, with proper settings of sweep rate and Y gain. That may be what the PROBE ADJ in the picture is, but I never saw an output on a scope before that didn't have a pin or loop that you could hang a probe on.

Lots more could be said, but maybe this is enough to get you started.
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David Kunkle
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Re: Problem with oscilliscope

Post by David Kunkle » Fri Sep 23, 2016 6:40 pm

Not the same one, but the same model. Did everything you suggested, but no change in the trace/dot. Even got the manual, but it's really no help at all. Seems to be written for an electrical engineer. The only thing I learned is that it's from 1971 and utilizes some kind of newfangled transistor thingies. ;) I thought it had vacuum tubes for as long as it takes to warm up and show signs of life.

Anyways, I think I accidentally applied line voltage to the probe ground, and now the dot won't respond to any input- so I think I fried it. Not much of a loss now at this rate. I'm prepared to call it a learning experience.

Now I'm looking at some used HP 54600B Digital 2 Channel 100MHz with storage capability on ebay for around $100. Any thoughts?
If your experiment needs statistics, you ought to have done a better experiment.

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Richard Hull
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Re: Problem with oscilliscope

Post by Richard Hull » Fri Sep 23, 2016 9:24 pm

Any 2 channel 100mhz storage scope is a steal at $100.00! Provided it is in flawless operational condition. Therein lay the rub. Very early storage scopes were crap! No modern scope is all that repairable. Custom house numbered components abound in these critters and the latest are microprocessor driven. Problems with your scope? Two places to take it....The manufacturer $$$$ or the dumpster.

I currently have 5 storage scopes of very modern vintage and three older, 80's, non-storage types and have owned many over the years. As an electronics engineer, I have used scopes for 56 years. Unless you are in HF radio and beyond, no one needs more than a truly good 60mhz scope, but 100mhz units are replacing them at the same price. If you are digital at all, you need the best storage scope money can buy. Beyond 100mhz, the scope probes tend to need to be "active" and very very special and hyper expensive.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Rex Allers
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Re: Problem with oscilliscope

Post by Rex Allers » Sat Sep 24, 2016 3:48 am

I agree with everything Richard said. Hard to cover important stuff in a few words, but I'll try.

I think the gold standard for analog scopes was Tektronics. I think all of them used CRT's as the display. One problem is that it will be hard to find a CRT analog scope with a CRT that has much or any life left. If you can't sit in front of it before purchase, that will be hard to tell. Here's a pic captured from one current eBay listing where they do show you something.
scope blooming.jpg
For this they do use the scope's internal square wave (as I mentioned in earlier post) as the source, so you can see it does sort of work. But the traces are big and fuzzy. Either they cranked the intensity adjustment up too high for the picture or the CRT is dying and you have to overdrive the intensity to see the trace. Buying would be a gamble, in my view. There are many others that are worse or show no useful signal for evaluation.

Analog scopes are good for seeing fast glitches in the signal, but for most stuff a good digital scope is just as good and is the only tool for looking at single or random events. Most of the digital scopes of the last decade or so don't use CRTs for display so should also last longer. Some digital scopes may let you download a captured trace to a PC via GPIB or USB but some may charge a big premium for this feature.

I have a Tektronics 2236 analog scope that is still working good, but the main scope I use is an Agilent DSO 3152A digital that I bought new around 2011. I think it is actually a re-branded Chinese Rigol scope. It has a 1 GSa/s sample rate, which is the key to performance rate for a digital scope, rather than bandwidth for an analog scope. The 1 GSa/s should be on the order of 100 MHz BW. A reasonable rule of thumb -- divide the sample rate by 10 for the effective bandwidth.

For new scopes, it looks to me that the safe buys start with Rigol models that begin in the $250 - $300 range. I also saw one used Rigol a little bit lower. Usable, properly rated probes and accessories (tips, adapters, etc.) are another thing you should factor in vs. used ebay listings.

It might be worthwhile to study a bit more before buying anything. The Australian guy who has the YouTube channel EEVBlog, might not be a bad place to start. I think he has a couple introductory vids on scopes. Here's a link to his channel posts narrowed to 'oscilloscope':
https://www.youtube.com/user/EEVblog/se ... cilloscope

Good luck. Unless you think you can narrow down to probable real bargains on used ebay scopes, I think I would recommend something on the order of a new ~$300 Rigol.
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Re: Problem with oscilliscope

Post by Jerry Biehler » Sat Sep 24, 2016 6:57 pm

Tek TDS340A scopes can be had for around $100. Great scopes, have lots of very useful functions like measurement and data capture.

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Re: Problem with oscilliscope

Post by Jeroen Vriesman » Sat Sep 24, 2016 7:30 pm

some time ago I bought one of these Chinese scopes, the type is UTD2052, and it was only 250 euro's new, with two probes.
bought it from aliexpress.com, they have newer types now, and usually Chinese specs are exaggerated by at least a factor two.

Besides making some noise (fan) and having to figure out how to set the language to English (default was Chinese) it's ok, the fft function is useless, but the rest is ok, not very good, bur for that price much more than you get form old analog scopes.

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Re: Problem with oscilliscope

Post by Jon Rosenstiel » Sun Sep 25, 2016 6:56 pm

Beckman 9022.jpg
David,

I have a Beckman 9022 that a friend gave me and I don't really need it.
Cost is free, but you pay the shipping.
Original manual included.

Please contact me if you'd like the scope.

Jon Rosenstiel
Last edited by Jon Rosenstiel on Sun Sep 25, 2016 9:12 pm, edited 1 time in total.

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Richard Hull
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Re: Problem with oscilliscope

Post by Richard Hull » Sun Sep 25, 2016 7:44 pm

Analog scopes are great and I retain two of them for video work. Yes, I am still 100% NTSC even on my giant flat sceen. 1080 what? Blue ray what?

Analog scopes do very well on mixed signal repetive waveforms, like video where they really are the cat's P.J.s. Digital scopes were crap on this for years and a few digital manufacturers realized this and put a special "video" mode selection on their scopes. Still sort of crappy.

Analog scopes are somewhere between terrible and worthless on glitches, (fast intermittent, irregular nasties on a signal line.) This is where digital storage scopes shine like a torch in th' night! A digital storage scope will catch and store those nasty bastards and leave you to figure out where you screwed up and work towards elimenating them.

As most of my work is now digital, those are what I tend to go to first and foremost. I tend to own and only like Tektronix but I have seen cheapo Rigols do great work as long as you don't push them to the brink. Tektronix has always tended to be a "closed shop"....(Buy only my stuff at my prices), even on their early low end digitals. They are waking up quickly due to the bottom line Chi-Com digitals filling up the low end market with scopes at half Tek's price and with features included in them that Tek used to force you to buy as extras!

Example: Teks earliest TDS digitals had zero features beyond a scope. Want RS-232? $395 plug in. Want GPIB? $495 plug in. Want math functions and fast fourier? another $400. Want RGB video output to a giant monitor? $350 plug in. Wanted parallel printer capability? $350, want storage to tranfer to a computer (floppy). Internal (buy a more expensive TDS) or external $500
The beat goes on.......They were one of the last companies to attach a standard USB port realizing a huge market for extras would close. So I have hated and loved tektronix.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Rich Feldman
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Re: Problem with oscilloscope

Post by Rich Feldman » Sun Sep 25, 2016 9:34 pm

David,

'Scopes are great tools & yours, if working, would be no exception. I think the step from analog bandwidth of 10 MHz to 60 or 100 MHz might open very few applications, depending on what you are doing. 10 MHz ( 35 ns risetime) will do for mains, audio frequencies, and many switched-power applications.

Digital storage makes it much easier to study single-shot events, as opposed to ones which repeat more than once per second. With it comes the ability to see the waveform at times substantially before the trigger event. Manhattan project observations got it done with analog methods.
http://electronicdesign.com/test-amp-me ... illoscopes

An important consideration in digital 'scopes is the sample rate, which (for periodic signals) can be much less than the useful analog bandwidth. There have been fine 14 GHz sampling scopes since the late 1960's. Can give high fidelity views of periodic pulses, TDR steps, and high-speed data eyes. Unable to capture isolated events.
220px-Tek-s-4.jpg
220px-Tek-s-4.jpg (9.46 KiB) Viewed 4633 times
The picture is from http://w140.com/tekwiki/wiki/S-4 . On many modern DSO's, you can observe periodic signals using time resolution much finer than the single-shot sample rate by selecting "Equivalent Time Sampling" mode, but that doesn't magically increase the front-end analog bandwidth.
All models are wrong; some models are useful. -- George Box

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