Found a TDS460 with jittery trigger - worth getting as a first decent scope? - Page 1
Forum section: electronics / testgear

author: NRoach44
author_rank: Contributor
timestamp: June 19, 2015, 03:04:26 pm
content: Hi again!I'm in the last stages of my exams and whileprocrastinatingtaking a breather I found a TDS 460 on Ebay. Considering the price, the relative scarcity of scopes in AUS, and it's specs I really want to jump on it. (4 inputs, and the only real feature I want is a decent single-shot capture mode)The only issue is that it fails the "ACQ and ACQ/ATTN" power on tests, and the seller says when attaching to the internal probe test the waveform jitters (on all four channels even!). I think I'd probably be capable of fixing it up (I can almost certainly use the Uni's equipment if need be). But the real thing is would it be a fairly easy thing to diagnose or would it be an utter pain in the arse? I've found copies of the service manual online but I haven't had too much of a read of them.Cheers!

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 19, 2015, 03:32:09 pm
content: Don't do it, seriously! All you would do is wasting your money.The TDS460 is a 20yr old scope with dire specs. It has 400MHz bandwidth but the sample rate is a lousy 100MSa/s which is insufficient to measure anything more than say a 50MHz (pure!) sine or say a 5MHz square wave.ACQ and ACQ/ATTN hints at a problem with the acquisition section, which may or may not be easy to fix. Even if it is easy, you're still left with an antique DSO with very poor performance data.I don't know the scope market in AUS but I'd guess they do sell something like the Rigol DS1054z, which is cheap and a much better investment than some old scraphead Tek.

author: NRoach44
author_rank: Contributor
timestamp: June 19, 2015, 03:38:11 pm
content: At this stage (starting bid + shipping) It's approximately 1/5th of the price of the DS1054z (which is the scope I'd end up getting otherwise).I was going to say that I'm not going to be doing 50MHz stuff but 5MHz square is pretty terrible. The sort of things I'd be wanting to do with it would be mainly switching power supply design, and maybe embedded stuff (where the rigol's serial decoding would massively help). I'm going to assume that it's probably not good enough even for this?

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 19, 2015, 03:56:48 pm
content: Quote from: NRoach44 on June 19, 2015, 03:38:11 pmSee, and even at that price it's still overpriced junk. Having said that, I wouldn't be surprised if the bid price jumps pretty high towards the end. Such scopes, although pretty useless, are often bought by amateurs that have no idea about scope specs and are lulled by the "Tektronix" label, and these people often pay excessive prices for such scopes which keeps prices somewhat high.QuoteNo, the TDS460 is pretty useless for any of that. It might be good enough for some audio stuff, but I guess for that even an old analog boatanchor is better than this Tek.This aside, if you want to dive into serious SMPS design then you're realistically looking at something like an advanced 350Mhz or better scope, preferrably with a good power analysis package. You may get away with something simple like a DS1054z but then you're only seeing a small part of the picture, and may be unable to find certain problems.But as a starter scope the DS1054z is fine.

author: NRoach44
author_rank: Contributor
timestamp: June 19, 2015, 04:01:12 pm
content: QuoteHeh, that probably would've been me.I'm not hoping to get too deep down the SMPS rabbit hole, more along the lines of basic 12v to whatever v converters for replacement chargers and the like.Cheers man! I'll hold off until I get the Rigol.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 19, 2015, 07:33:37 pm
content: Quote from: Wuerstchenhund on June 19, 2015, 03:32:09 pmWhat kind of shit is this?It says 400MHz on the panel. Do you misbelieve their statement? The rated rise time is ~1ns. Do you misbelieve that as well?It will not do fastsingle eventsamples, but that is rarely a problem. Even the famous avalanche pulse generator circuit repeats often enough to resolve its waveform easily (if not particularly quickly).The bandwidth is several times greater than the 1054Z, so saying it will never measure a sharper waveform is downright stupid.Anyway...QuoteMost likely bad electrolytics, which were all over the 460 and similar (but not the -A). Buy it if you don't mind replacing caps. The menus also are slow and awkward to navigate. It's a perfectly fine instrument, as acquisition and accuracy goes, just not the handiest for bench work.Tim

author: nctnico
author_rank: Super Contributor
timestamp: June 19, 2015, 08:04:33 pm
content: Quote from: Wuerstchenhund on June 19, 2015, 03:32:09 pmSorry but that is just nonsense. It has 400MHz bandwidth which it achieves using equavalent time sampling. With the right probe it will show a 50MHz sine or square wave perfectly (within the given bandwidth limits). The problems are most likely caused by leaking capacitors which can be hard to fix if the electrolyte has eaten away PCB traces. A Rigol 1000Z has a lot of features but it doesn't have the 400MHz bandwidth which will be handy every now and then! Back in the day I used to have a 100MHz general purpose scope and one older scope with a higher bandwidth for the odd jobs.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 19, 2015, 09:06:56 pm
content: Quote from: nctnico on June 19, 2015, 08:04:33 pmIn fact, come to think of it -- the trigger and ADC have even more bandwidth than rated, if you don't mind that it's in the stop band. I've observed signals over 600MHz before -- not at nominal amplitude, of course. But that's absolutely something you won't see on a 1054Z: RTS scopes must have a hard bandwidth cutoff. EQS scopes can afford a much more gradual passband, much like some of the older instruments (I've observed 400MHz on my Tek 475 before -- same idea).(Not everything can do that, even analog scopes. Tek's fastest tube scope had a rather abrupt stop band, due to the multiple distributed amplifiers used in the signal path. Not to mention the lumped equivalent delay lines. Both exhibit a strong asymptotic attenuation in cutoff (think -100s of dB/octave), arguably as the price to pay for extending the passband modestly with those techniques.)Tim

author: nctnico
author_rank: Super Contributor
timestamp: June 19, 2015, 10:29:57 pm
content: These older Tektronix scopes with equavalent time sampling do have a pretty good trigger system and a Gaussian frequency roll-off (very gradual to avoid phase shifts in the signal). My 500MHz Tektronix TDS744A would happily trigger on 1.2GHz signals.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 19, 2015, 10:31:46 pm
content: Quote from: T3sl4co1l on June 19, 2015, 07:33:37 pmThe only thing that's stupid is your comment, really. The "shit" is some pretty stubborn physical and mathematical facts that you're apparently oblivious to.For starters, the fact that the analog bandwidth of the TDS460 is 400MHz is irrelevant when the max real-time sampling rate is 100MSa/s, and the mathematical reality is that 100MSa/s are only enough to digitize a 50MHz sine wave. And "sine wave" here means a 100% perfect sine wave, something that you won't ever see in the wild, because almost everything that you think is a sine wave also contains other frequency components. And if the signal is not a perfect sine wave then the useable bandwidth won't even be 50MHz but a lot less.Even worse, for something like a lowly 5MHz square wave the TDS460 will only show up to the 9th harmonic, which means you already loose some of the higher frequency components that make up the waveform, and what you see on the screen will be noticeably distorted compared to the signal you try to measure.Oh, and as to ETS mode: yes, the TDS460 can do Equivalent Time Sampling, and indeed it can make use of its full analog bandwidth in that mode. The problem with ETS is that it is only valid if the signal is 100% repetitive, i.e. no jitter, no runts, no random glitches. If there are any changes between the individual acquisitions then the displayed waveform becomes invalid, which is another mathematical reality. That means ETS is plain shit for most debugging tasks where the idea is to identify changes in a signal.ETS was a crutch at a time when the real time sampling rates of DSOs were as poor as they are for the TDS460, and has very little value in this day and age.And now we have a young fellow who wants to know if the TDS460 would be a good starter scope for things like working on SMPS, something a 100MSa/s DSO is completely useless for because of it's horrible real-time performance (and again, ETS is completely worthless for non-repetitive signals).Seriously, if you believe that the TDS460 is a great scope for that you're either deluded or cluelessQuote from: nctnico on June 19, 2015, 08:04:33 pmI'm really not a big fan of the DS1000z (or Rigol kit in general) but at least it is able to make use of its whole bandwidth in real-time mode, which is somewhat important for stuff you know like finding glitches, runts or other signal deviations. The OP mentioned SMPS, and that means finding glitches and checking signal variations. ETS is absolutely useless for that, and without ETS your useable bandwidth on the TDS460 is limited by the atrocious sample rate.And btw, the max update rate of the TDS460 is somewhere around 200 to 500 wfms/s, compared to what, 30k wfms/s on the Rigol?Still think the TDS460 makes a great beginner's scope?QuoteAm I right when guessing that these were analog scopes? As in scopes that can make use of their full bandwidth in real-time?This aside, we're no longer "back in the days" where even basic scopes cost a fortune. These days even little money buys you some remarkable devices, so there's really no need to resort to old crap like this scope. In fact, I'd say even an old analog scope would be a better choice than this TDS460.

author: dom0
author_rank: Super Contributor
timestamp: June 19, 2015, 10:55:52 pm
content: Expect electrolyte leaked all over the analog PCBs, if it saw use after the caps spilled, expected lots of eaten PCB tracks, dissolved components etc.These scopes with this kind of damage are often beyond economical repair.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 20, 2015, 12:19:26 am
content: Dear Wuerstchenhund,Thanks! Most brilliant satire I've read all day.

author: rs20
author_rank: Super Contributor
timestamp: June 20, 2015, 12:34:12 am
content: Quote from: T3sl4co1l on June 20, 2015, 12:19:26 amSeriously? Care to explain where the satire is? ETS being useless for the enormous majority of usecases seems like a correct assertion to me. And that was the only subjective/potentiallywrong thing in his post.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 20, 2015, 01:07:32 am
content: Quote from: T3sl4co1l on June 20, 2015, 12:19:26 amI seriously can't tell if he's insane or just trolling.

author: rs20
author_rank: Super Contributor
timestamp: June 20, 2015, 01:16:50 am
content: OK, time out everyone. All of this "insane" / "trolling" / "satire" talk is completely cowardly and unproductive. See a claim you think is wrong? Then make a counterclaim. This isn't YouTube.ETS is only useful on perfectly repetitive signals. Wuerstchenhund's claim is that perfectly repetitive signals are sufficiently rare that a scope which such poor realtime performance will cause a lot of confusion, especially for beginners. Is this what you disagree with? Or something else?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 20, 2015, 03:22:50 am
content: Quote from: Alex Eisenhut on June 20, 2015, 01:07:32 amTo be fair, the better a satire gets, the more indistinguishable it becomes from the thing it aims to make fun of.I thought about just leaving no replies at all. I thought better of it by attempting to acknowledge the satire, rather than leaving it up to the reader to weigh the value of the post -- a method that surely would backfire upon its author.Quote from: rs20 on June 20, 2015, 01:16:50 amYou're right, it's worse: YouTube with all the comments and none of the video.Specifically, what I was laughing at was the absurd string of troll level statements, combined with straw man after straw man.But if you insist...First of all:QuoteCitation needed.QuoteIt's patently false, yes.Required reading before continuing:http://www.wescottdesign.com/articles/Sampling/sampling.pdfExample from the lab:I have here an avalanche pulse generator. Not a very good one, and much more periodic than I would've liked for the example.I have another generator, which has a quite nasty repetition frequency indeed. It averages about 100kHz, but the delay between events varies widely, give or take a factor of 2 or more. The pulses look something likethis, except you'll have to imagine the irregular sawtooth profile consists of full (rather than partial) discharge events.That generator has decided not to cooperate (and I don't feel like poking it to make it work). So you will have to take my word that this series works just as well for aperiodic, repetitive signals.The first is under "real time sampling" conditions. Let us examine the assertions:Quote from: Wuerstchenhund on June 19, 2015, 10:31:46 pm(First note: none of my quoted statements (trimmed) were addressed individually. So I have already been discriminated against by not being given the benefit of an orderly, rational exchange.)The first waveform above is "zoomed out" under "real time" conditions, as displayed.According to the above assertion, there should be absolutely, positively no features visible with a pulse width under about 10ns.At 500ns/div, and 1 div being about 50 pixels wide, one pixel is about 10ns (which corresponds to the 100MS rate, after all).In fact,three pulsesof nearly 100% amplitude are visible. They are only one or a few pixels wide, but they clearly were sampled, somehow. Curiously, not all pulses were sampled at the same amplitude. It's impossible to see on a static photograph of course, but the actual display flickers wildly, so that you can clearly see some peaks are higher or lower. The repetition rate is a bit under 2MHz, so according to the above, no harmonics above the 25th should ever appear (or any wave shape that would be equivalent to their presence).All of which is inconsistent with the display, which clearly shows sharp behavior. No, you can't measure the actual risetime from here, but that's precisely as much a fault of the visual display as of the sample rate: if the signal changes in one pixel, then it must be, at most, 10ns -- but it could be much, much shorter.And yes, if you perform a DFT (Discrete Fourier Transform) on the displayed data series, you -- by definition -- won't see anything above what corresponds to the 25th harmonic: but that's trivial, because the data set simply does not have any finer data. It could be sampled in such a way to contain finer timesteps, but it's not configured to do so at these settings. Thinking that is a failure of the instrument is directly akin to cursing the sea when the tides roll in!Likewise, it also doesn't contain any low frequency (extremely coarse) data: from this one picture, it wouldn't be obvious if there is, say, a 60Hz component riding on the trace -- you'd have to zoom out to see it. But that's true of any instrument, as you need to be reading on a suitable scale in order to resolve a signal or component of a similar scale!Quote(Does this not utterly contradict the proceeding statements, which were presented absolutely, without exception?... Anyway...)QuoteAgain, you will have to take my word that the above waveforms need not be perfectly periodic, with unknown amounts of jitter, or runts, or random glitches. But the display looks just the same, when zoomed in to the same scale.QuoteThis is a very mushy statement, so of course I can try to pin down something, but I will inevitably be "missing the point of it" in so doing. So, again, I make this reply only grudgingly;If the trigger fires, causing a sampling event, then a new set of data will be added to the display.It's important to note that the signal need not be periodic, because the trigger ensures that the sampled data remains temporally coherent to the signal.If that set is sparse (i.e., ET), it will be interleaved with the existing data. (In this way, a complete image is built up over time, by sampling at random offsets.)If the set of new data is inconsistent with the data it replaces, or its adjacent data, then an apparent error will appear. The usual manifestation is an overly jaggy or noisy and shimmering trace, where potentially every other sample is damn near random.The fact is, in the vast majority of cases, this is not a problem. And in the situations where it is of consequence, understanding the nature of that image is of greater value than seeing it all blurred together, such as on an analog oscilloscope.(To put it very frankly: if you're too stupid to read what a DSO is telling you, you probably shouldn't be reading one in the first place. Please don't impose your stupidity upon others. Please allow for the possibility that others may be more capable than yourself.)Seeing it properly sampled, at full acquisition and analog bandwidth, of course is better, but there are few situations where this is insufficient.In my work with power supplies, I find it more than sufficient. I have no trouble determining what part of the waveform I am looking at, or during what part of the cycle, if it has a slower repeating modulation (e.g., line rippleQuoteNow we leave the domain of signal theory and enter the mushy realm of personal preference.It would be much simpler, and much less ingenuous, to make a simple statement of fact such as,QuoteRather than projecting your preference onto all others, when using a statement such asQuoteNot to out-do himself, one final straw man:QuoteI'm afraid I don't know what mental age you come from, but in polite, adult society, it is possible to be simultaneously supportive of, and critical of, a subject. When you grow up*, you will realize that one can defend something, without the necessity of endorsing the things it represents. Some dude named Voltaire I think had a famous quote to this effect.Curiously, I never once offered my personal opinion on this instrument, yet I am being attacked as though I thought it was the best thing since sliced silicon.(*I'm using age as a metaphor here, not as an attack on the person's physical age. I would like to use the analogy of mental age, but alas, many legal adults also seem to make the same type of mistake on a regular basis, so that wouldn't be as apt as the idealized metaphor.)Anyway, back to my waveforms. Zooming in, clearly, it is resolving the full ~1ns rise/fall and 2ns pulse width, which corresponds to the nameplate 350MHz bandwidth. The physical sample rate might be quite a bit less than 25GS (indeed, it's probably substantially less than 100MS given the poor refresh rate), but that clearly hasn't affected the waveform one bit! So as you can clearly see, when the analog bandwidth is greater than the Nyquist rate, it is no problem whatsoever to acquire signals and waveforms much finer than the Nyquist Reconstruction Theorem would suggest. Stating otherwise illustrates only how poorly the detractor understands the theorem! If this pulse train were filtered to a bandwidth more typical of the sample rate (i.e., 20-50MHz at 100MS/s), the peak amplitudes would never be greater than about two divs, and they would always be consistent. The narrow (and seemingly stochastic) pulses are proof that higher bandwidth is available, and working -- and that aliasing is working, as well.Now, this is where aliasing is harnessed as a benefit, rather than thrown away as interference. When one thinks to understand what aliasing is, rather than rejecting it with prejudice as confusing and unnecessary -- one finds great value in this characteristic of periodic sampling.In this case, it happens that, most of the time, the peaks won't be picked correctly, but sometimes they will. When one builds a statistical collection of these events (such as by viewing the dancing waveforms in real time), it becomes obvious that there is more information to be seen here. Just as one can see faint peaks on an analog scope trace, and knows to zoom in on them for closer inspection. They can also be highlighted with the Peak Detect or Envelope mode, or filtered as nuisances using the Hi Res mode (or reduced analog bandwidth, or both). An immediate consequence of aliasing comes out of this: if the signal is periodic, then the difference between fundamental and sample rate (or the harmonics of either) show up periodically, as determined by the ratio of the two rates. In the first waveform, the peaks on the left seem to be sampled well, while the peaks on the middle and right were cut short. One can use the pulse height as an indicator of vernier time with respect to the sampling event, and in fact, resolve time divisions much smaller than the 10ns/pixel displayed on the screen.Using a frequency domain view instead, one can see a triggered (= phase locked to some rational ratio to the fundamental) ET sampler as a mixer, where the harmonics of the signal are mixed with the harmonics of the trigger frequency. When these differences are fully accounted for, the baseband signal becomes an exact downshifting of the original signal, given that it be rebuilt in order. (This analysis requires periodic signals; of course, by invoking harmonics, we imply the use of the periodic Fourier transform, which by definition is not aperiodic.)This is easiest to see when the number of samples per trigger event is large, but reordering random samples by timestamp has an exactly equivalent result, so we don't mind.Tim

author: nctnico
author_rank: Super Contributor
timestamp: June 20, 2015, 10:23:54 am
content: Quote from: Wuerstchenhund on June 19, 2015, 10:31:46 pmAs usual: if the price is right. 'if you spend more you can get something better' is more than true of oscilloscopes.An analog scope shows signals using it's full bandwidth. The theory that is... Occasional spikes won't show up especially at high sweep rates when the trace already gets dim from sweeping fast. On both a slow sampling DSO and analog scope you have to setup the triggering to capture a spike. The DSO (even with equivalent time sampling) is more likely to show something meaningful than an analog scope.

author: G0HZU
author_rank: Super Contributor
timestamp: June 20, 2015, 09:22:02 pm
content: QuoteCan you explain to me how the the (deluded and/or clueless?) people at Texas Instruments managed to use a 'completely useless' Tek 460A in their test procedure for this DCDC converter design?http://www.ti.com.cn/cn/lit/ug/sluu429b/sluu429b.pdfQuote

author: Rupunzell
author_rank: Frequent Contributor
timestamp: June 21, 2015, 03:44:13 am
content: Quote from: G0HZU on June 20, 2015, 09:22:02 pmTexas Instruments power division still uses more than a few items of "vintage test gear" some here would consider to be old-obsolute and in the way of modern stuff. This was verified by a recent visit to Ti.Bernice

author: ebastler
author_rank: Super Contributor
timestamp: June 21, 2015, 06:12:01 am
content: May I remind everyone of the original poster's key requirement:Quote from: NRoach44 on June 19, 2015, 03:04:26 pmThat should make it pretty clear that he needs a scope where the sampling rate matches the bandwidth, for single-shot, real time sampling, right?

author: NRoach44
author_rank: Contributor
timestamp: June 21, 2015, 06:23:00 am
content: Quote from: ebastler on June 21, 2015, 06:12:01 amTo clarify I'm not sure if that's as important as I feel it is, but I mentioned that because it's what I sorely miss on my terrible 10MHz CRO.I feel that the more higher-spec sorta things I'd do with it would be the power-on of a SMPS. But I'm not entirely sure what I foresee myself using it for, other than "Lets have a look at this circuit is doing".So far it looks like I'll get the DS1054z and see how that suits my needs.

author: PA4TIM
author_rank: Super Contributor
timestamp: June 21, 2015, 07:30:57 am
content: Quote from: T3sl4co1l on June 19, 2015, 09:06:56 pmI have a 547, it is a 50MHz scope. It still triggers and shows a 150MHz sinewave see:http://www.pa4tim.nl/wp-content/uploads/2011/08/547_150MHzsinus.jpgand it shows a 20 MHz square as :http://www.pa4tim.nl/wp-content/uploads/2011/08/547_20HMzblok.jpgThis is the same signal on a 280MHz version of the Tek 7704Ahttp://www.pa4tim.nl/wp-content/uploads/2011/08/7704_20MHzblok.jpgWith the 1S1 plugin the 547 is a 1 GHz sample scope. I think the old sample scopes are a bit like the early DSO's. They are good for repetitive signals. So no things like runts or glitches.The "williams" avalanche pulser on a 1S1http://www.pa4tim.nl/wp-content/uploads/2012/01/williams1.jpgandhttp://www.pa4tim.nl/wp-content/uploads/2012/02/williams2.jpg"zoomed in"But that does not say much, here the same pulse on a 7 MHz analog scopehttp://www.pa4tim.nl/wp-content/uploads/2012/02/HM108williamspuls.jpgAnd finally on a modern 350 MHz DSO from Hameghttp://www.pa4tim.nl/wp-content/uploads/2012/02/WPtestopbouw.jpgBesides a whole bunch of analog scopes I had a 100 MHz Rigol, DS1102, and for a while a Tek 210 from a friend. According to many one of the worst scopes Tek made. I used the Tek more often as the Rigol. I used my analog scopes more then the Rigol. I do not have the Rigol anymore. I gave it away because I hated that piece of crap (buttons fell of or refused to work, the probes lasted a few months, the power button stopped working, several push buttons gave problems and it was blind for glitches and runts. I did reverse recovery time measurements with it and did the same one on the Hameg DSO.http://www.pa4tim.nl/wp-content/uploads/2010/11/1N4148.pngthe Hameghttp://www.pa4tim.nl/wp-content/uploads/2010/11/1n4148Trr_1S1.jpgon a 7704Ahttp://www.pa4tim.nl/wp-content/uploads/2010/11/1n4148.pngon the RigolBut besides that. I would not buy a broken DSO from that area for trouble shooting SMPS's as it is your only scope. They can be a challenge to repair. I have no experience with that scope my self but I repaired a hybrid Tek 2710 SA and that was not an easy job. The biggest problem can be finding special Tek parts. That is, I assume those scopes a stuffed with that like they did in the 7000 series scopes and 27XX SA's. And if caps are the problem then first check the SM and count the caps, good caps are not cheap. Someone told me about a Tek DSO he repaired, I do not remember the type and I did not checked his statement but he replaced over 200 caps (that sounds a bit unbelievable to me but I'm to lazy to count them) ;-)I would not buy a Rigol too >:-)I am not anti-DSO, I was, until I bought the 350 MHz Hameg. I repair test and calibration gear as a living and use it every day, I love it. I use it 95% of the time.I still use a 547 because it can do some things modern scopes can not (I have a lot of plugins), and because it is compact and has cursors a Hameg HM1004 (most times coupled to a Tek current probe amp and a Tek Diff probe amp) A 7603 is coupled to a power meter. A 453, 7704 and a 1GHz Philips sample scope are stored under the benches but fully operational.A good DSO can do almost everything needed. But an analog scope too (Nasa did not have DSO's in the 60's, that did not stopped them from getting on the moon ;-) )But a good DSO is a powerful instrument that has many handy things and is comfortable to use.I I had to choose between a good working 400 MHz analog scope, an early 400MHz equivalent sample time DSO and a 400MHz real time DSO. I would choose the last one. If I had to choose between the first two I choose the analog scope. If I only had one option, a bad number 2, I would invest the money in a good multimeter. >:-)

author: Howardlong
author_rank: Super Contributor
timestamp: June 21, 2015, 07:52:38 am
content: If it helps, I've owned a TDS460A that I recently sold (http://www.ebay.co.uk/itm/131491415225?ssPageName=STRK:MESOX:IT&_trksid=p3984.m1559.l2649) but I found, after some months, that after an introductory period, I very rarely used it in preference to other scopes I had, including an MSO1074Z (MSO version of DSO1074Z, but I almost never need to use the LA though with four analogue channels) and old school 2467B CRO.The reason for its lack of use on my bench was, quite simply, the TDS460A's user interface. I didn't find the UI at all intuitive, it was a fight to do anything. That together with it being really sluggish, meant I found myself automatically switching on the 2467B and/or the Rigol. Boot time was also a concern on the TDS460A, and that is the reason why the 2467B is popular. It remains a mystery to me how Tek could create a scope like the 2465 series with such an intuitive UI and move to the swamp-like UI on the TDS460A. The (recently) much-maligned TDS200/1000/2000 series had/have a much better UI that's also reasonably responsive.Regarding the equivalent time sampling vs real time debate, you can _usually_ use ETS or indeed a CRO by being smart with your triggering and/or being inventive by repetitively recreating the scenario with a lash up. Often in the MCU world this is easy to achieve by popping in a couple of lines of code.I find it mildly amusing that we have these debates on the merits of real-time vs ETS and the merits of deep memory for example, because when I were a lad, such luxuries didn't exist and we made do. We just got creative with our testing and analysis, and, in some ways, we probably learned more that way too.By the way, that scope sale I did included four fully working 400MHz/500MHz Tek probes with proper hook clips, ground leads and all accessories. It probably demonstrates why all too often probes aren't included in scope sales, the value of those probes alone is probably $200, I doubt it added anywhere near that value to the sale.Edit: grammatical error correction.

author: tggzzz
author_rank: Super Contributor
timestamp: June 21, 2015, 08:09:04 am
content: Quote from: Wuerstchenhund on June 19, 2015, 03:32:09 pmThat is the correct conclusion, but...Quote... is nonsense.Consider a scope which was state-of-the-art in its time, cost as much as a small house, andstillsells for thousands of pounds/dollars: the HP54120. It has a 1GHz bandwidth and 40MS/s. I used it to accurately characterise sub-nanosecond risetimes either of repetitive waveforms or via eye diagrams.General principle: use a scope to assure/ensure signal integrity, then debug digital signals in the digital domain.If it worked, then a 400MHz scope would be able to show ~1ns risetimes.

author: tggzzz
author_rank: Super Contributor
timestamp: June 21, 2015, 08:19:39 am
content: Quote from: Howardlong on June 21, 2015, 07:52:38 amVeryverytrue!

author: Howardlong
author_rank: Super Contributor
timestamp: June 21, 2015, 08:24:13 am
content: Quote from: PA4TIM on June 21, 2015, 07:30:57 amFunnily enough, I used that exact analysis while drafting my last post!

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 21, 2015, 11:57:57 am
content: I'll address this in a single post because it starts becomming really ridiculousQuote from: tggzzz on June 21, 2015, 08:09:04 amNo, it isn't. It's a simple physical fact, something that it seems quite a few people are completely oblivious to.But no need to believe me, lets see what others have to say, for example LeCroy:http://cdn.teledynelecroy.com/files/whitepapers/wp_ris_102203.pdf(for those that don't know, 'RIS' is the name of the ETS mode in LeCroy scopes)To quote:"...These characteristics impose serious constraints on the use of RIS. The fact that the waveform is produced out of multiple waveform segments acquired at different, random points in time limit the usefulness of this feature to specific applications. In order to use RIS, the application must meet the following requirements:1. The waveform must be repetitive.2. The trigger event must be identical for every sweep.Repetition is the key. RIS makes the assumption that every waveform segment that is acquired is the exact same analog waveform. Furthermore, it assumes that this same analog waveform is triggered at that exact same place in the waveform on every acquisition. The only difference assumed is that the sampling phase (where the trigger occurs with relation to samples) is changing.These restrictions on repetition are serious. It means that the waveform must be repetitive, the trigger must be stable, and no non-repetitive nature of a waveform, like jitter etc. can be measured properly in this mode. Failure to honor these restrictions results in severely distorted waveforms with no usefulness whatsoever and erroneous measurements.[...]"But I guess that is nonsense, too, then, right?QuoteTalking about nonsense, a 54120 does not sell for "thousands of dollars" and hasn't for a long time:http://www.ebay.co.uk/itm/Agilent-HP-Digitizing-Oscilloscope-54120B-amp-54121A-Four-Channel-Test-Set-54121T-/281634203129?pt=LH_DefaultDomain_0&hash=item4192b4e5f9http://www.ebay.co.uk/itm/HP-54120A-Digitizing-Oscilloscope-High-Bandwith-/161653491383?pt=LH_DefaultDomain_0&hash=item25a34c86b7&nma=true&si=T8PVOxP4hsdfbxTQRQKwYh88G%252FI%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557You must have mixed up 'asking price' with 'market value', since just because some sellers want some ridiculous amounts for their old scrap doesn't mean they'll find anyone paying that. There's some demand for the "T" variants which do TDR (although even these scopes don't sell for "thousands of dollars"), but not much for the basic 54120. The same is true for essentially any other old sampling scope these days.Price aside, you also completely ignore the fact that the 5412x Series was a special purpose high bandwidth scope made for a very limited set of measurements (u/t histograms, eye diagrams, and time domain reflectometry with the "T" variants; HP used a special technique for creating valid eye diagrams with these sample scopes) and *not* a general purpose scope. Great for you that back in the days you were able to use the scope for what it was designed, but that does not change the fact that a sampling scope like the TDS460 or even the HP 5412x are pretty poor general purpose scopes. This is why back in the days no-one would have used a 54120 as a general purpose scope, and went with an analog scope (the standard general purpose scope of that time) instead.Quote from: Howardlong on June 21, 2015, 07:52:38 amI'm happy for you that you have such find memories of yesteryear, but you and the others here are missing the plot.You and the others are completely oblivious to the fact that this thread is about a beginner who is looking to buy his first general purpose scope, which he wants to use for things like working on SMPS stuff. You seriously suggest that a 100MSa/s sampling scope is great for these things?Once upon a time people had to do with out antibiotics and medicine was mostly limited to stuff like blood letting with leeches, and still many survived, but it would be plain stupid to recommend to go back to the methods of these times. However that's exactly what you lot are suggesting. Since the around 2000 DSOs have become better general purpose scopes than analog scopes thanks to fast processing, samplers and memory, and since a few years prices especially at the entry level have dropped dramatically so that even a few hundred dollars buy you a pretty fast brand new scope. At no time it was easier for a beginner to get a decent entry level general purpose scope.Quote from: T3sl4co1l on June 20, 2015, 03:22:50 amAh, the arrogance of the ignorant. It was just a matter of time that the "you're too young" strawman was pulledMy age is just one of many things you apparently don't know, so I'd recommend to stop speculating and wild-guessing. But for the sake of not letting you die in complete ignorance, let me just tell you that I'm much closer to retirement than to graduation, and just because I'm not one of the (sadly too many) engineers who are stuck in their old ways and are incapable to make the mental leap into the modern age doesn't mean I'm a youngster, or that I've never used such equipment 'back in the days'. It just means I'm not oblivious to the fact that technology has moved on a lot since then, and that what was great 25 years ago may not be that great in this day and age.What's really annoying is that the 'backwarders' in this forum regularly claim superiority of analog scopes even in this day and age because of their perceived speed, which is critical to see signal anomalies like runts etc. Now essentially the same group comes to this thread to convince a beginner to forgo all technical progress of the last 20 years to buy a scope that is even slower than a even a mediocre modern DSO. You couldn't really make this stuff up, seriously, if it wasn't so sad that many seem to be completely oblivious to the mathematical and physical facts and limitations behind ETS.However, the really sad part is that none of this crap is helping the OP to make a sane decision, and has a very good chance to cost him a lot of money for a useless pile of junk that after spending money for getting it fixed will very likely be insufficient to do what he needs it to do.@NRoach44:I'd suggest you send Dave Jones (the EEVBlog presenter and owner of this forum) an email and ask him if he'd recommend a TDS460 (or any sample scope for that matter) as a suitable beginner's scope for what you want to do. My money is on that he'll tell you roughly the same as I did (that these days yu should stay away from these antique DSOs) to get a modern DSO instead.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 21, 2015, 12:03:44 pm
content: Just as a little demonstration, the following screenshots show a few of examples how great a 100MSa/s sample rate and ETS is these days, compared to say the 1GSa/s that even low end beginner scopes like the Rigol DS1000z Series offer these days.The source is a Rigol DG1062z AWG which isn't great but does the job for these examples. The scope is a LeCroy WavePro 7300A 3GHz 4Ch scope (reference clock is provided by an external GPS disciplined OCXO), which has been bandwidth-limited to 200MHz.The first signal is a simple standard 5MHz square wave @ 4Vpp. Even though it's just 5MHz, the screenshots show noticable degradation at 100MSa/s.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 21, 2015, 12:05:02 pm
content: Now the same with a 15MHz square wave.The degradation is even worse, which is because at 100MSa/s important frequency components are undersampled.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 21, 2015, 12:13:07 pm
content: The next example is a demonstration of Equivalent Time Sampling vs. Real-Time Sampling.Since the scope only offers RIS (ETS) mode for higher sample rates in excess of 20GSa/s), these examples won't show the bandwidth limitation that would be inherent if the sample rates were as low as on the TDS460 (see the real-time samples I posted before), i.e. the conditions are much better than they would be for a TDS460. And still, it shows how useless ETS is as a general debugging tool where signals are usually non-repetitive.The example shows a 5MHz square wave @4Vpp which is pulse-modulated (500kHz, 75deg phase). That's a type of signal that can be found e.g. in power electronics and is a good example of a typical signal someone would want to debug.The ETS waveform is just utter crap.

author: EEVblog
author_rank: Unknown
timestamp: June 21, 2015, 12:20:51 pm
content: Quote from: Wuerstchenhund on June 19, 2015, 03:32:09 pmYup, 100MS/s isn't worth the trouble.

author: rs20
author_rank: Super Contributor
timestamp: June 21, 2015, 12:26:53 pm
content: This remains one of the dumber debates I've seen on this forum. I'm pretty sure that almost all of the participants are aware that a 400 MHz, 100MSa/s scope has these capabilities:-- Single-shot/real time mode: Fails with any frequencies/harmonics past 50 MHz (wording softened thanks to Tim's link), and don't think that it works at all well at 30 or 40 MHz either.-- ETS mode: 400 MHz bandwidth.And, that if ETS mode is presented with a signal that is not perfectly repetitive (I said periodic in the past, Tim's example showed I should have said repetitive), it will display all sorts of corrupted data. So,-- SMPS startup transient behaviour, SMPS load transient behaviour, SMPS with a jittery/unstable feedback loop: ETS unuseable, effective bandwidth well below 50 MHz-- Any kind of remotely interesting AM/FM signal: ETS unuseable, effective bandwidth well below 50 MHz-- etcOn the other hand,-- A steady-state SMPS working perfectly stably and reliably: ETS useable, 400 MHz bandwidth. But, I dare say that there's a catch 22 buried here somewhere.-- Avalanche generators, eye diagrams: Sure, 400 MHz -- but again, beginners??-- etcSo uh yeah, ETS is useable sometimes and sometimes it's not. Woo.

author: EEVblog
author_rank: Unknown
timestamp: June 21, 2015, 12:29:53 pm
content: The problem with scopes like the TDS460 is that you are paying for the bandwidth, yet getting pretty horrible sample and update rate that will lead to a generally miserable experience in everyday use compared to any modern digital scope.If bandwidth is what you are after cheap for repetitive signals then I'd recommend an old analog scope.For a general purpose scope, especially one for a beginner, I'd rather have a modern 50MHz DS1054z than any other old scope (analog or digital) with 5 times the bandwidth any day of the week. It will be a much more useful scope.

author: EEVblog
author_rank: Unknown
timestamp: June 21, 2015, 12:34:32 pm
content: Quote from: rs20 on June 21, 2015, 12:26:53 pmThat is why practically all general purpose digital scopes since the TDS220 (20 years ago!) have had real time sampling, generally 5-10 times the bandwidth.ETS is just awful and there is no point using a scope that uses it in today's market.

author: G0HZU
author_rank: Super Contributor
timestamp: June 21, 2015, 12:45:10 pm
content: Note that the OP only seems to want to look at designing basic DCDC converters for stuff like battery chargers etc. Plus a bit of simple stuff with PIC/AVR.If scopes are scarce where the OP lives and the price is a fraction of the cost of an alternative then the only 'significant' issue I see is that the scope was described as having a jitter issue. This should be reason enough not to buy this particular TDS460 IMO despite the apparent confidence about ease of repair etc.It isn't a scope that would appeal to me so if time permits I would wait to see what other scopes appear for sale. But if I desperately wanted to play with simple DCDC converters and the only scope immediately available in my budget/location was a TDS460A for maybe £50 then I'd buy it.It is possible to do useful DCDC converter work with a TDS460 even if it has obvious limitations with the sample rate.There are loads of devices and application notes for basic DCDC converter design and as long as the design guidelines are followed for layout and the designer uses parts recommended then you really don't need to do much with the scope except maybe look at a few waveforms (with a sample rate well below 100Msps). Even then you could get a high success rate even with no scope at all provided you build it correctly to the application note. I expect there are loads of people out there who have done this.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 21, 2015, 12:48:49 pm
content: Quote from: rs20 on June 21, 2015, 12:26:53 pmIndeed, it certainly is.QuoteThe catch is that ETS doesn't provide sufficient data to say if the SMPS is really working stable, as the waveform on the screen might be completely bogus.Back in the old days I've observed many times situations where engineers watched a waveform on a sample scope and thought that because the waveform looked fine that everything was A-OK, when it really wasn't, but that this was overlooked because the engineer didn't appreciate the limitations of ETS. Which wasn't uncommon, as back then the standard scope was analog, and many older engineers only moved to DSOs after they offered sensible real-time sampling rates, so often had little contact with ETS. Hell, it even shows in this discussion.Quote from: EEVblog on June 21, 2015, 12:34:32 pmThank you!

author: NRoach44
author_rank: Contributor
timestamp: June 21, 2015, 01:09:40 pm
content: Cheers guys!I do appreciate the effort you went to Wuerstchenhund with the screen caps - they demonstrate something I can understand. As much as I tried to undestand the post T3sl4co1l made, I couldn't.For reference the scope sold for ~AU $92 with what would have been ~$60 postage . I'm in no big rush as I could use the expensive Keysight scopes the Uni has, but it would be nice to have it at home.:http://www.ebay.com.au/itm/Tektronix-Model-TDS-460-Oscilloscope-Parts-or-Repair-/251994991813?

author: nctnico
author_rank: Super Contributor
timestamp: June 21, 2015, 01:27:03 pm
content: Quote from: EEVblog on June 21, 2015, 12:29:53 pmI wouldn't. I have been down the high bandwidth analog scope road before and analog scopes suck worse than a DSO with equivalent time sampling. A DSO typically has a longer memory so you can zoom in, save the trace to a disk and the trace isn't getting dim due to the high sweep rate.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 21, 2015, 01:38:35 pm
content: Quote from: G0HZU on June 21, 2015, 12:45:10 pmScopes may not be as readily available in Oz as in the USA or Europe,but they are not that scarce.It's Australia,for Pete's sake!------Not some coral atoll in the middle of the Pacific.Perhaps the OP should look around a bit more.If he is poor,by the time he has spent the money & time fixing the TDS 460.he could buy something more appropriate.

author: G0HZU
author_rank: Super Contributor
timestamp: June 21, 2015, 01:48:15 pm
content: QuoteWhen I read the first post in the thread I assumed the OP was in some remote part of Oz and had found a scope locally on ebayBut it now turns out the scope in question was for sale in the USA!$71 USD would have been fine for that scope if it had been working properly. I could certainly have used it for basic DCDC converter design and I doubt I would have even needed the full 100Msps.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 21, 2015, 01:54:19 pm
content: Quote from: G0HZU on June 20, 2015, 09:22:02 pmSure, they could because the switching frequency of this particular circuit is hundreds of kHz range. Which conforms with my initial statement that the TDS460 is pretty useless above say 50MHz for a pure sine and say 5MHz for a square wave.But I guess (I hope!) you already knew that and just wanted to add more stupid arguments that miss the mark completely to an already painful thread. Well done!

author: G0HZU
author_rank: Super Contributor
timestamp: June 21, 2015, 02:11:45 pm
content: QuoteThe OP wanted to design simple DCDC converters for battery chargers. Therefore, I think the various arguments about the limitations of ETS are largely irrelevant.I tried to look at the strengths of the instrument wrt the task in hand. The TDS460A offers decent sensitivity, 100Msps and a decent record length. All for $71.

author: NRoach44
author_rank: Contributor
timestamp: June 21, 2015, 03:05:51 pm
content: Quote from: vk6zgo on June 21, 2015, 01:38:35 pmI'm going to try and be as less confrontational as possible, but please don't keep saying I "should look around more".I'm only really going to spend up to about ~$300 total on the scope if it's used (and if it's approximately comparable the 1054z, because I'd probably have to buy probes, won't have the warranty, etc.) and unless it's miles better than the 1054z that isn't going to change.Take into consideration that I probably will use the extra inputs on the Rigol.Just to get it out of the way, let's look at element14:http://au.element14.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=43&storeId=10184&categoryId=800000019504&sort=P_PRICE&pageSize=25&beginIndex=1&showResults=trueTheir cheapest scope is a Tenma (their generic brand) 2ch 25MHz 250MSa/s for $527pre taxThat also appears to be the same basic unit that Altronics sell.Let's look at craigslist Perth's electronics section:http://perth.craigslist.com.au/search/elaIt's not even worth searching for oscilloscope.Gumtree perth:http://www.gumtree.com.au/s-perth/oscilloscope/k0l3008303Occaisionally they do pop up here, but it's either terrible or I don't have the cash while it's available.Ebay (filtering for used and worldwide):Kikusui: Freight. It's going to be bloody expensive.Triumph: A nice relic but I'm not collecting.Tek 7633: Produced from 1974. I'll pass.Tek 2440: Actually doesn't look too bad, but holy shit that power on test.Tek 485: 2 chan, 350MHz. I feel I'd use the channels more than the frequency. $360Tek TDS320: Over cost without freight.Tek 2465: not bad, but over cost without shipping againFluke 92B: Over cost, not worth it IMOProtek p2020: 20MHz. PassTek 2465: About same cost as the Rigol, marked as "FOR PARTS"Tek 465B: Half as many channels as the Rigol, for 120% of the priceHP 1715A: $200, might be worth considering if it wasn't for Parts/Repair, with no probes.Tek T935A: That frequency and that cost? Not even with the "Great! Cool!" in the title.Tek 485: Almost at the budget but is sold as-is.HP 1722B: As previous but ancient and only dual input.Hitachi V355: Dual input, 35MHz. Looks fairly simple.Tek 2440: Again, looks OK but the seller mentions "The device has intermittent start-up errors, fails the self test, and has a weak display... adjustments and repairs will be required and should be expected."Tek 2465A: Over budget but not bad. Has been red stickered but apparently the seller can't find any fault.Tek 2430A: No shipping, not touching it. (Probably expensive)Tek 222: Looks like a nifty little machine, but doesn't use standard BNC probes, need an external power brick (probably actually a good thing) and is only dual input.This is where I gave up (I'm not going to bother writing more about them). There is another Tek 222 later on that I may consider but it still comes down to the following:Do I spend $200-$300 on an Okay-ish scope with 2 channels, and probably end up switching to the Rigol later anyway? These scopes also don't have serial decoding.I am not touching a PC scope as I would like my PC to not be tied to old hardware or software.Edit: Clarifications.

author: nctnico
author_rank: Super Contributor
timestamp: June 21, 2015, 03:58:13 pm
content: The way I see it you have 2 choices: get an old boat anchor with a bandwidth of several hundred MHz or buy an entry level Rigol or Siglent scope with a 100MHz or lower bandwidth. The Rigol or Siglent will have long memories, serial decoding, saving data to a USB stick, measurements, etc. The downside is that you will need to spend money if you need a higher bandwidth because there just isn't a cheap option to get that. Either way I wouldn't buy an old boat anchor if it has a bandwidth of less then 300MHz.

author: Howardlong
author_rank: Super Contributor
timestamp: June 21, 2015, 04:32:20 pm
content: Quote from: nctnico on June 21, 2015, 03:58:13 pmI'd largely agree with that.Also, for SMPS as well as MCU stuff, four channels is super useful. I also haven't seen anything that the OP would want to do that would benefit from significantly higher bandwidth than 100MHz. Sometimes higher end MCUs benefit from higher bandwidth, but for the most part not.From the OP's last post, if they can run to a DS1054Z, I would do it compared to the other options.

author: mikerj
author_rank: Super Contributor
timestamp: June 21, 2015, 04:42:18 pm
content: Quote from: Wuerstchenhund on June 21, 2015, 11:57:57 amA pure sine or square wave is repetitive waveform and as such could take full advantage of the equivalent time sampling up to 400MHz. Calling other people oblivious is a bit rich if you overlook such basics.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 21, 2015, 08:23:51 pm
content: Quote from: mikerj on June 21, 2015, 04:42:18 pmOh, well, another joker who forget to use his brain before starting to typeWhile you're right of course that a pure sine wave would be repetitive and thus valid even in ETS mode, it's pretty useless unless your work is looking at known-to-be perfect sine waves, because (aside from the fact that it's very unlikely you'll find a perfect sine wave in nature, even less so on any circuit you're trying to measure something) ETS still won't show you any non-repetitive signal components like glitches and other crap, which is usually the reason why you'd want to use a scope in the first place (and this was about a general purpose scope, remember?). That means ETS is still pretty worthless to debug even unicorn-made generators producing perfect sine waves, which means any debugging of such miraculous device is still limited to the scope's real-time mode, and that means max 50MHz sine waves, and only if they're perfect.But yeah, feel free to try another selective quote to, maybe it works better next time

author: c4757p
author_rank: Super Contributor
timestamp: June 21, 2015, 08:26:06 pm
content: Play nicely, children. I'm all out of popcorn.

author: nctnico
author_rank: Super Contributor
timestamp: June 21, 2015, 09:01:14 pm
content: Quote from: Wuerstchenhund on June 21, 2015, 08:23:51 pmYes it does. Have you ever used a scope which used ETS? Glitches will show as an unstable part of a signal and because ETS is usually slow it stays there long enough to get noticed. ETS is not some kind of glitch filter! The only really important thing when using ETS is that you need a stable trigger. Once you know there is a glitch you can adjust the trigger accordingly to get a better picture of the glitch.

author: guido
author_rank: Regular Contributor
timestamp: June 21, 2015, 10:51:45 pm
content: I'm nog going to take part in the the whole debate, but i don't think such a TDS would be good as first scope. Specially if it's broken. There are hardly any schematics around (i think) and it is likely to use special tek parts. And to fix a scope you quickly need another one. On top of that, those series have a problem with leaking smd caps, so you need to start restoring tracks.So for now get something really cheap and a separate logic analyser. These are cheap these days if it is only for serial decoding. If you have the money later, buy a good modern scope.I'm actually restoring a TDS430A at the moment, problem with the monitor section (thank god no leaky caps in later models). Paid 40 euro's at a ham fest. Note i was more interested in the, like new, 400MHz probe in the bag on topAlso have a 2430A here (which came to me even cheaper), it's also only 100MS/s with 150MHz front-ends. It has it's uses. Main scopes are analog ones, still don't had the need to get a modern scope. But then i like fixing up old stuff.As to your list:Tek 222:verylimited bandwith.Tek 2465: Probalby needs new caps in the power supply (mine did). The A version has a big chance of leaking caps. They are high end analog scopes, with a high price tag if you need any tek parts to fix them. Not a beginners scope (unless it's a good one at a bargain price obviously. But that accounts for anything working).Tek TDS320. Same as the 460; leaky caps, schematics, performance.Tek 2430A. Same 100MS/s. Re-capped mine (no leaky caps, just worn out). Same tek specific parts again.Tek 2440. Expect new caps for the supply. Tek specific parts again. But better at 500MS/s.Tek 7633: I have a few 7xxx main frames, use them for specific plugins. Expect that you need to work on them now and then. Replacing power supply caps for example (see the pattern emerging?). Very heavy and therefore $$$ to ship around.The others seem overpriced (and the fluke is a handheld, you pay a lot for that).If the Hitachi is very cheap and local, it might be good to get you going. But indeed, it's back to basics.

author: NRoach44
author_rank: Contributor
timestamp: June 22, 2015, 02:57:47 am
content: Yeah, I already got a HP 1662C for $200 shipped, which I'm quite happy about and it did help with an assignment.As it is I don't see the likely hood of a 4channel reasonable bandwidth scope that's in good condition appearing for a price within my range. I just felt I needed to demonstrate this to the people who keep saying "you aren't looking hard enough"Thanks guido, this is the sort of thing I was looking for when I asked on the forum. I think I'll leave buying old scopes until I have the space, time and willingness to repair them.

author: rs20
author_rank: Super Contributor
timestamp: June 22, 2015, 04:04:30 am
content: Quote from: nctnico on June 21, 2015, 09:01:14 pmMmm, if you define "show" as "display in the form of glitchy, apparently-high-frequency corruption that is completely confusing to a beginner, completely irrelevant to a discussion prompted by a self-styled beginner, and when discovered, would necessitate that the user in question either figure out an advanced triggering mode* to isolate the glitch or switch to an oscilloscope with non-awful realtime performance like a ds1054", then yeah, I guess you are pedantically,technicallycorrect.* Yes, pulse width triggering mode is advanced for a beginner.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 22, 2015, 04:07:45 am
content: Quote from: NRoach44 on June 21, 2015, 03:05:51 pmGumtree & Craigslist are a waste of time,so you are left with eBay.Again,if it isn't in Oz,it's a waste of time & money.Another possibility is the Perth Hamfest,which is in the beginning of August,& often has cheapie Oscilloscopes.If you object to all & every one of the 'scopes on your list,it looks like you may as well save up for the Rigol.I don't have one,or any DSO,for that matter,but the Rigol brand has a good reputation on this forum,so it would be my choice.

author: edavid
author_rank: Super Contributor
timestamp: June 22, 2015, 04:13:40 am
content: Quote from: guido on June 21, 2015, 10:51:45 pmI disagree with the probably; I have several, and none of them have bad power supply caps. Only the 2465B has the leaking cap problem.QuoteIt's a lot different, since it's 500MSPS. It's a nice scope, except for the lack of memory. Schematics are available for the TDS340A/TDS360/TDS380, and are usable for the TDS320.

author: NRoach44
author_rank: Contributor
timestamp: June 22, 2015, 04:20:56 am
content: Quote from: vk6zgo on June 22, 2015, 04:07:45 amIf I search ebay with "up to $300, australia only" on top of the previous search, there's 28 results. I'm not going to go through them all, but long story short there's only mostly 2chan low-bandwidth scopes, and vintage machines.I went to the Perth Hamfest last year, there was the 10MHz DSE scope I have now, and a vintage dual channel there too. I went with the DSE as it would actually fit in my bag. I'll probably end up going this year as well, but I doubt there'd be a decent scope there this time either.I am definitely going to purchase the Rigol now, as a few of the posts here (when they aren't arguing about ETS) go on to say something along the lines of "If it's old it's not worth it for a beginner*, doubly so if it's broken"Edit: *at least for my use cases any way.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 22, 2015, 05:45:41 am
content: I remember now,you're the bloke who uses public transport.Unfortunately everything is geared to cars,so anything that isn't light becomes a nightmare.That said,I took an old Desktop,complete with CRT monitor & keyboard, home on the bus back in the 1990s-----never again!I Googled for the TDS460,& lots of people seem to have the "jittery" problem.I was surprised that it was quite a compact unit--some of the really old DSOs from the late '80s,early '90shad massive great raster displays & were nearly as heavy as a 7613,plus were an awkward shape.Most of the early DSOs were pretty horrible for realtime use due to lack of memory depthTo get around this,they reduced the sample rate for long times/div,which is OK if you aren't trying to look at analog video at field rate,or 50Hz hum on a pulse train.Aliasing makes a total mess of things.That put me off DSOs for ages,but modern ones are light years better!

author: NRoach44
author_rank: Contributor
timestamp: June 22, 2015, 05:53:11 am
content: Heh, I've got a friend who is on his Ps and has a car nowI'm on the "do 25 hours of driving and wait 6 months" stage myself, but due to living on campus at Uni I can't just ask the parents to supervise me.The other thing is I'd rather not get another big machine like the HP 1662C as it's already enough of a pain in the arse to move my stuff around before I got the HP.Emona's Perth branch isn't too far away. I'm going to try and call them to see if they have one in stock that I can pick up.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 22, 2015, 09:53:15 am
content: Quote from: nctnico on June 21, 2015, 09:01:14 pmYes, I have, actually quite a lot back in the days when scopes had very poor real-time sampling rates.QuoteWrong! *Some* glitches (i.e. those that have a high occurrence rate) are somewhat visible on ETS, and if they're large enough you might even recognize that there's a problem. That doesn't change the fact that most common glitches and problems simply very likely won't show up in ETS.QuoteNot in ETS, because even with advanced triggers ETS won't miraculously show signal deviations it hasn't shown before. And without ETS you're back to the bandwidth limitations of the poor real-time sample rate.Fact is that you can't use ETS to probe unknown signals (or signals with unknown components), because for ETS to remain valid you have to establish that certain signal parameters are valid (i.e. repetitiveness) even before you start your measurements. You may or may not see something which you believe is true but unless the stringent requirements of ETS are met it very likely isn't. So ETS completely worthless for that, which probably rules out a majority of debugging tasks already.Your reply shows very well the typical fallacy that people who don't appreciate the severe limitations of ETS often fall into. Sure, you can find situations where ETS shows you signal deviations, and you can certainly construe situations (which others have in this thread) where a signal sampled in ETS looks somewhat similar to the same signal sampled in real-time mode, but these are very limited border cases which don't change the physical realities, and it would be stupid to assume that just because it seems to you as ETS is perfectly useable that this is generally the case, because it isn't.And even if you don't want to accept the maths/physics behind ETS then just ask yourself this: if ETS was as sufficient for common debugging work as you and others in this thread claim it is, why don't we see more new sample scopes? I guess Rigol and Siglent could drop their prices even further by using slower ADCs and using ETS instead. But reality is that sampling scopes have mostly disappeared aside from some cheap-ass USB "scopes" and the upper high end (i.e. bandwidths in excess of 50GHz to 100GHz) and even in the latter area they are dying out in favor of real-time scopes. Even more so, ETS mode is also slowly disappearing in newer scopes as well. And the fact that they are means that there's probably a good reason for it. Go figure.You (and all the others that made this thread to one of the most embarrassing ones I've seen on this forum) can continue to keep your head in the sand of course but reality is that, as a general debugging tool, ETS is downright useless. You might actually have a better chance of finding random glitches in your signal by reading fish guts than with ETS.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 22, 2015, 12:05:26 pm
content: Quote from: rs20 on June 22, 2015, 04:04:30 amOne only needs to think in terms of what digital sampling means, in order to figure this out. None of the detractors in this thread seem to appreciate DSOs as DSOs; if one wills that a cat should act like a dog, one will forever have the problem that it is a fundamentally different creature...Not for a beginner? Probable. But a beginner will have trouble getting a stable display on an analog or RTS DSO all the same, so it's a pointless argument.Quote from: Wuerstchenhund on June 22, 2015, 09:53:15 amJust what kind of signals are you watching that have such infrequent glitches? And at a bandwidth much greater than typical?To use your very own example of SMPS startup conditions, consider that SMPS rarely peak above 1MHz, and those are the small ones. That's 1000ns per cycle. 500ns per on-period. At 100MS/s, you have a whopping 50 samples to observe the pulse width variation in real time.If you're looking at glitchy high speed data, you simply have the wrong instrument, period. You need a logic analyzer with that type of capability. Preferably with a glitch trigger setting, or something like that.So again, your arguments are invalid.QuoteHave you an example of such analiensignal?So far in all of my work, I have not seen a single situation that was obfuscated by ETS. (The prior case of runt square waves is easily solved with advanced trigger, or a single capacitor to the trigger input.)QuoteDuh. Marketing. ADCs are cheap enough that the analog signal path is the limitation now. It would cost quite a bit more to design and build a preamp that's capable of driving the full ADC's analog bandwidth (which is usually a few times its max. Nyquist frequency).They can also charge more for the scopes that do offer extreme bandwidth.It's also a cost saving feature to avoid ET hardware and software. Although with everything going through an ASIC, it's up to the functionality in there. But even having that in the first place, Rigol (and Keysight) get tremendous value in performance and production cost.QuoteWhen cost is no object, you might as well get the best.I'm not concerned about the design of scopes that cost more than a small house.Tim

author: guido
author_rank: Regular Contributor
timestamp: June 22, 2015, 04:49:38 pm
content: Quote from: edavid on June 22, 2015, 04:13:40 amGuess your lucky with the PS caps but others are not (i wasn't for starters and you can find more examples if you google around). Those caps start to bulge. With regards to the leaky caps on the A5 board, you are right.As to the TDS320, i missed the sampling rate spec. The schematics are there indeed, i use the doc for the monitor pcb in my 430A. But the schematic of the monitor isonly partlythere (if you have the full pdf, i'm very interested). When i looked around on the net i think i saw two TDS manuals with schematics in total.As for the topic starter; if you would buy a second hand scope it is a good thing to check first if you can find the schematics on the net. And if it is easy to get parts.