DSO Reliability

[Alex Eisenhut]

7834 ("fast" storage) but still perhaps HP1727A storage writing speed is better.

When those things were in their prime the failure rate of the storage tubes was horrible. The HP storage tubes worked a lot better than the Tektronix ones, but they were just as bad for early failures. Warranty on a new scope in those days was 90 days, and Tek and HP replaced a lot of tubes under warranty. If a tube lasted through warranty it tended to go on for quite a while, unless the user insisted on always turning up the brightness to full. Failures outside warranty were really bad news, as a new tube was a large part of the price of a new scope. However, it seemed like if you got a good sample of tube it went on and on working nicely. Maybe all the machines still in existence have those golden samples of tube in them.

The large Tektronix storage tubes, which were the mainstay of the early CAD industry, had a far more predictable life, but it wasn't that long. A well used terminal needed a new tube in less than 2 years.

On my HP1741 there was a conventional mode that turned off the storage, at least you could get a trace if the storage part was dead.

[rf-loop]

I would never recommend the 7854 to anybody unless they had a very specific need because its complexity leads to complex failures.

I wouldn't recommend an analogue storage scope to anyone for anything. Their time passed long ago.

7854 is not analog storage scope. It is early digital (storage) scope. (it is analog but it have (slow) digitizer and then this "famous" waveform calculator keyboard (discrete keyboard with full of functions)
500kSa/s and up to huge 1024 points memory and 12 10 bit vertical resolution.

Of course all these are (mostly) museum equipments, not at all for everyday use. But sometimes it is "nostalgic" try things as we have done long time ago, and yes we did very complex things some times.

EDIT: corrected vertical resolution
(as David Hess and datasheet tell my memory was bad)

[David Hess]

I would never recommend the 7854 to anybody unless they had a very specific need because its complexity leads to complex failures.

I wouldn't recommend an analogue storage scope to anyone for anything. Their time passed long ago.

As rf-loop points out, the 7854 is not an analog storage oscilloscope.

A 7834 analog storage oscilloscope was the least expensive way for me to get a 400 MHz storage oscilloscope of any kind.

7854 is not analog storage scope. It is early digital (storage) scope. (it is analog but it have (slow) digitizer and then this "famous" waveform calculator keyboard (discrete keyboard with full of functions)
500kSa/s and up to huge 1024 points memory and 12 bit vertical resolution.

The 7854 has 10 bit horizontal and vertical resolution with a CRT to match although even with 256 x 315 DPI, they did not call them retina CRTs.  I was surprised but should not have been when using one that the 10 bit resolution can show signal details which are completely lost on old or new 8 bit DSOs.

[coppice]

I would never recommend the 7854 to anybody unless they had a very specific need because its complexity leads to complex failures.

I wouldn't recommend an analogue storage scope to anyone for anything. Their time passed long ago.

As rf-loop points out, the 7854 is not an analog storage oscilloscope.
A 7834 analog storage oscilloscope was the least expensive way for me to get a 400 MHz storage oscilloscope of any kind.

Yeah, I mixed up the model numbers.

[XFDDesign]

To the original question, everything is made like it's Disposable now.

I also got a scope from the 465 family (475) as a first-scope. It still runs today, but I gave it to a friend back in 2005. That same year, I bought my first Digital Scope, a TDS5032B.

Three-quarters of the way through the warranty period, it crapped the bed. Tek was proper and did a warranty job on it (HDD failed). Since then, it's had reliability issues - something on the windows operating system craps the bed too. You have to flatten and reinstall. A few months ago, I decided to buy the jitter analysis software - a simple dumb unlock key.

Tek stopped supporting the scope about four years ago. Including software keys. Go to Tek.com, and try to find anything on the TDS5000 series, and you're better off playing a Rogue-like on Tourist mode (near impossible). This also means that 'free money' to them is not something of interest. A month later, the scope just outright failed and is bricked. It was something I worried would happen.

When I bought it from the proceeds of my first major contract, it was $7,300 new. The same thing "today" from Tek is $15k. It's till PC based too, which means the whole of your instrument is held in the balance upon consumer products (the computer) lasting. In other words, modern gear today is built as a commodity, while commanding instrumentation grade dollars, and must be expected to die in 3-5 years.

My TDS5000 scope will be replaced with a Rigol shortly, because if it's a choice between a $15,000 something that will die in 3 years, and a $5,000 something that will die in 3 years, I am better off not spending the extra $10k for the luxury of having "Tektronix" printed on the front.

[J-D-H]

I'm pursuing the 465 repair, but unless I get very lucky, it looks like it may take awhile.  Depending on what I find, doing the repair my be rough.  At least it has no surface mount parts to contend with, so that's good.  However some of the circuit boards are NOT convenient to work on.  So I'm measuring my options while also troubling shooting the old scope.

Most common 465 failures are repairable and in rough order of likelihood include:

• Shorted solid tantalum capacitors - the power supply is well designed so this is rarely catastrophic.
• Worn out aluminum electrolytic capacitors - The 465 has a linear power supply and this is easy enough to repair.
• Failed high voltage z-axis DC restorer - The high voltage capacitors or diodes sometimes become leaky.  If this is suspected it is usually best to just replace the parts involved.
• Failed tunnel diodes result in a loss of triggering.  Sometimes just calibration is necessary to fix this because apparently their characteristics change over time.  Replacement tunnel diodes are a problem.
• Failed high voltage multiplier - The oscilloscope will work without it but not well; usually if it fails it shorts out the high voltage supply but not catastrophically.  Replacements are often available and it is not difficult to build one.

All or most of the 465 series oscilloscopes discussed over on TekScopes@yahoogroups.com have been repairable.  Offhand I do not remember any that were not.  Some diagnostics however are best done with another working oscilloscope which can become a step down the path to collecting them.

What about modern analog scopes rather than these inexpensive (a relative term) DSOs?  If there are 100 MHz scopes being made with fewer "digital features", maybe I would be better off buying something like that for general home hobby projects and ham radio work?

I do not think a new analog oscilloscope would be any better than a cheap but new DSO.  I suspect you will get more life out of a repaired 465 than either and with care even buying one or two 465 oscilloscopes to use or as parts donors will be significantly less expensive.  I went the later route as the cheapest way to get a workable DSO and ended up with a pair of 2230s (I repaired and recalibrated both) which at this point have already outlasted some new DSOs.

I just found the failure in my 465 - a blown small signal PNP in a TO-18 can in the middle of the vertical deflection plate driver board.  And I also found that these parts are socketed -- how nice (had not known that before!).  I just ordered the replacement parts, so I should be back on the air soon.  I am still interested in buying a DSO, but at least the pressure is off.

BTW, the seller of the repair parts I need (the transistors) is very familiar with Tektronix gear and how my 465 compares to these modern DSOs (he refurbs scopes).  When it comes to reliability, he had little good to say.  He mentioned that they use domed (or membrane?) keyboards which have a limited service life (maybe 4-5 years?).  He also described how these modern DSOs implement the FFT spectrum analyzer function (or at least how many of them used to do it).  I was blown away when he said most have no calibration for this function -- IOW, no freq scale.  He also said they have no means to adjust the freq scale.  It sounded like he was describing more of a toy than anything else when it comes to the FFT aspect.  He did mention that they get better all the time, so that it's possible that the latest units might have a more worthwhile and useful FFT capability -- but I suppose he wasn't sure of the current state of the art.

[J-D-H]

Having my Tektronics 465 fail recently was certainly depressing (great general purpose scope, IMO), but this does give me the opportunity to buy something new!  So I'm searching for a new dual trace scope with around 100 MHz BW, and settled on getting one of the ~many~ apparently Chinese made DSOs selling in the $400-450 range.

If you were happy with the 465 then why not fix it or buy another?

Then look at evaluating a new DSO in slow time. I can pretty much guarantee you will find things about a modern DSO you will not like and things you will like (in comparison to the old 465).

The best combo is to have the 465 and a DSO to get the best of both worlds. Another reason to fix the 465!

The other thing to be wary of is fan noise. Quite a few DSOs can be very noisy and this can be very distracting if you are used to working in a fairly quiet environment at home.

I'm pursuing the 465 repair, but unless I get very lucky, it looks like it may take awhile.  Depending on what I find, doing the repair my be rough.  At least it has no surface mount parts to contend with, so that's good.  However some of the circuit boards are NOT convenient to work on.  So I'm measuring my options while also troubling shooting the old scope.

What about modern analog scopes rather than these inexpensive (a relative term) DSOs?  If there are 100 MHz scopes being made with fewer "digital features", maybe I would be better off buying something like that for general home hobby projects and ham radio work?

Na don't go there. 
This oportunity to get a DSO and move into a new(for you) type of test gear should not be missed.
There is so much even a entry level DSO can do that is not possible with your 465.
This you need to experience for yourself.

Grab the link from the first post in the Repair board for help with your 465 repair.

Fan noise for the Siglent SDS1000 series has never been an issue IME.

As just described in another reply, my 465 is soon to be fixed.  However I will continue to look into these modern DSOs!

[J-D-H]

At the risk of getting off topic, what's wrong with the 465?  They're pretty easy to repair for the most part.

Just found it -- a blown small signal PNP.  Parts are on order, so the 465 will soon be up and running again.  I still want to look more into these DSOs though.....

[J-D-H]

Hearing about the less than stellar firmware was an eye opener.  If this is typical across all brands of these low end DSOs, maybe I should look for another solution....

How about a somewhat newer second hand scope? There's plenty of stuff available which for most part is pretty reliable.

And buying used means you can get more/better features (i.e. proper FFT) than on new entry-level scopes.

What about modern analog scopes rather than these inexpensive (a relative term) DSOs?  If there are 100 MHz scopes being made with fewer "digital features", maybe I would be better off buying something like that for general home hobby projects and ham radio work?

"analog scope" and "modern" is an oxzmoron, considering that the big brands have stopped making them many years ago, as has CRT production in general.

I just met an equipment refurbisher who educated me as regards "modern" test gear.  It was quite an eye opener.....

[tautech]

Congats on the find and hopefully a full repair.
So often another scope is needed to repair another. 
Nothing like keeping your eyes open though for the obvious.

Good call to proceed with the purchase of a DSO, you will marvell at their capabilities.

[J-D-H]

One aspect of scope design that is common to both types is the ruggedness of the user interface. Back in the 1960s and 70s the designers knew that a scope would see a lot of use and the switches and controls were big and solid and well engineered.

But over time this has changed. I'd certainly question how long the buttons and controls will last on a modern scope and how well it would survive a drop. Maybe they will be very reliable but back in the 1980s a lot of test gear proved very fragile and unreliable in this respect. Especially from HP.

I expect the modern design driver for a low cost DSO is to make something that is rugged enough to last for a few years' regular use before it gets upgraded. A bit like a laptop PC.

I was just old that many (most?) of these entry level DSOs use rubber dome keyboard-style front panel switches which have very limited service life.  If so, my old 465 switches are tank-like by comparison.

[J-D-H]

I guess to some extent it comes down to your idea of a 'standard' bench scope. Rigol and other Far Eastern manufacturers have created a whole new market for scopes that offer tremendous capability at a consumer price point, which I couldn't have dreamed about when I was learning electronics and doing it as a hobby. But they're not really up to the job of being an 'every day' scope in a working laboratory, not because of their spec sheets, but because they don't have the ease of use and reliability necessary.

I've been using low end Chinese DSOs as everyday scopes for professional work for years. I can't remember one ever failing, and I only rarely need to reach for a high end scope because the cheap one isn't up to the job. Most lab work is really pretty undemanding of an oscilloscope, unless you are in one of a few niche activities. Most really serious work is done with more specialised tools, like spectrum analysers or precision measuring instruments.

So you have seen no problems with the panel controls?  I was just told that 3-5 years is a typical life span for these DSO panel controls -- especially for the dome type push buttons.  Wrong?

[tautech]

One aspect of scope design that is common to both types is the ruggedness of the user interface. Back in the 1960s and 70s the designers knew that a scope would see a lot of use and the switches and controls were big and solid and well engineered.

But over time this has changed. I'd certainly question how long the buttons and controls will last on a modern scope and how well it would survive a drop. Maybe they will be very reliable but back in the 1980s a lot of test gear proved very fragile and unreliable in this respect. Especially from HP.

I expect the modern design driver for a low cost DSO is to make something that is rugged enough to last for a few years' regular use before it gets upgraded. A bit like a laptop PC.

I was just old that many (most?) of these entry level DSOs use rubber dome keyboard-style front panel switches which have very limited service life.  If so, my old 465 switches are tank-like by comparison.

Membrane keypads (switches) have been around for decades.
In 20 year old Teks I have never seen a problem.
They are in everyday life and their greatest problem is with moisture that is not normally a problem in the lab.

[J-D-H]

Congats on the find and hopefully a full repair.
So often another scope is needed to repair another. 
Nothing like keeping your eyes open though for the obvious.

Good call to proceed with the purchase of a DSO, you will marvell at their capabilities.

If what I was told about the limited usefulness of the FFT function in these DSOs is true, I must admit that some of my interest has dissipated.  However, who knows, maybe the spectrum analyzer aspect is better now....

[J-D-H]

One aspect of scope design that is common to both types is the ruggedness of the user interface. Back in the 1960s and 70s the designers knew that a scope would see a lot of use and the switches and controls were big and solid and well engineered.

But over time this has changed. I'd certainly question how long the buttons and controls will last on a modern scope and how well it would survive a drop. Maybe they will be very reliable but back in the 1980s a lot of test gear proved very fragile and unreliable in this respect. Especially from HP.

I expect the modern design driver for a low cost DSO is to make something that is rugged enough to last for a few years' regular use before it gets upgraded. A bit like a laptop PC.

I was just old that many (most?) of these entry level DSOs use rubber dome keyboard-style front panel switches which have very limited service life.  If so, my old 465 switches are tank-like by comparison.

Membrane keypads (switches) have been around for decades.
In 20 year old Teks I have never seen a problem.
They are in everyday life and their greatest problem is with moisture that is not normally a problem in the lab.

Maybe so, but my experience with dome switch computer keyboards has been less than stellar.  Of course this may be an apples to orange comparison, but I'd still rather see more robust hardware (for a few bucks more, of course).

[xwarp]

If what I was told about the limited usefulness of the FFT function in these DSOs is true, I must admit that some of my interest has dissipated.  However, who knows, maybe the spectrum analyzer aspect is better now....

Here I've been reading through this thread thinking I might want to look into one of the newer Rigols, but for what I work on at home, the TDS460 I have should serve me pretty well.

Still trying to figure out some things about it though.

[coppice]

Maybe so, but my experience with dome switch computer keyboards has been less than stellar.  Of course this may be an apples to orange comparison, but I'd still rather see more robust hardware (for a few bucks more, of course).

You don't have a choice. All modern test equipment uses the same kind of switches, from the cheapest DSO, to the most expensive exotic comms analysers. Some examples of these switches are a bit better made, but they are all pretty similar. The biggest problem comes when heavy units need to be moved. Its very common for one or two of the switches to take a big enough hit from the mover that you end up with damage - often a switch ripped right out of the membrane sheet. These can be very costly to fix. You can't go to anyone but the original source for a replacement membrane, and they can charge whatever they like. A short time after production stops the supply of suitable spares will dry up. These are the real issues with membrane switches, not general wear and tear.

As for computer keyboards, your view might be distorted. If you have trouble and open up a keyboard you will find it is a membrane type. However, almost all the ones which don't give trouble are also the membrane type. Only a small quantity of specialised keyboards, like those available from pckeyboard.com, are not membrane ones.

[XFDDesign]

If what I was told about the limited usefulness of the FFT function in these DSOs is true, I must admit that some of my interest has dissipated.  However, who knows, maybe the spectrum analyzer aspect is better now....

I'm not sure what you were hoping to get from the FFT engines.

There is a pretty simple way to organize the "useful range" of an FFT: your max frequency will be set by your sample rate, your frequency bins will be set by the maximum window. (Rough approximation)

Example: I have my scope set to 100us/div, with 10 divisions width. My sample rate is set to 800ps/pt (1.25GSPS). Fmax will be 1/2 your sample rate (625MHz) and the bin width will be 1/(10*100uS) = 1kHz which will also set the minimum frequency of the window. Processing 1,250,000 points will take a big chunk of time too.

Dynamic range will also be crap. Most of the 8-Bit ADCs might get 6 bits ENOB. Even with all of the other sampling tricks you can pull, you won't have a very good "noise floor" with the FFT.

Call me a curmudgeon, but I'd be more concerned about having a scope that is primarily a scope and not a gimmick box that happened to start life as a scope.

[TunerSandwich]

If what I was told about the limited usefulness of the FFT function in these DSOs is true, I must admit that some of my interest has dissipated.  However, who knows, maybe the spectrum analyzer aspect is better now....

Call me a curmudgeon, but I'd be more concerned about having a scope that is primarily a scope and not a gimmick box that happened to start life as a scope.

Curmudgeon....

[TunerSandwich]

Congats on the find and hopefully a full repair.
So often another scope is needed to repair another. 
Nothing like keeping your eyes open though for the obvious.

Good call to proceed with the purchase of a DSO, you will marvell at their capabilities.

If what I was told about the limited usefulness of the FFT function in these DSOs is true, I must admit that some of my interest has dissipated.  However, who knows, maybe the spectrum analyzer aspect is better now....

You can most certainly buy something like a Meyer SIM system is you want proper FFT.....buying a scope for FFT seems a bit backwards though....most of the scope FFT functions I have used are painfully slow, have limited range and are lacking in resolution to be of any significant use.....other than taking a glance into defining a starting point for proper spectral analysis

to me the biggest problem with modern DSO's is the lack of external clock sync and tools to time align with other acquisition tools.....that baffles me beyond any of the other potential "problems" with these tools...

[David Hess]

He also described how these modern DSOs implement the FFT spectrum analyzer function (or at least how many of them used to do it).  I was blown away when he said most have no calibration for this function -- IOW, no freq scale.  He also said they have no means to adjust the freq scale.  It sounded like he was describing more of a toy than anything else when it comes to the FFT aspect.  He did mention that they get better all the time, so that it's possible that the latest units might have a more worthwhile and useful FFT capability -- but I suppose he wasn't sure of the current state of the art.

The issue here may be that many DSOs do not apply the correction factors needed to produce a calibrated output making them difficult to use in place of a spectrum analyser.  This EDN article discusses it:

http://www.edn.com/electronics-blogs/the-practicing-instrumentation-engineer/4427466/DSOs-and-noise-
http://www.edn.com/electronics-blogs/the-practicing-instrumentation-engineer/4427466/2/DSOs-and-noise-

[Wuerstchenhund]

If what I was told about the limited usefulness of the FFT function in these DSOs is true, I must admit that some of my interest has dissipated.  However, who knows, maybe the spectrum analyzer aspect is better now....

You get what you pay for. The Rigols all have very poor FFT which only uses a few hundred points, and I'd assume (haven't checked if the figure is out there) that Siglent SDS1000/2000 scopes use similar low numbers which they do because their processing is dog slow.

Really old DSOs often use something around the 10kpts mark which, while being much better than modern day Rigols, is still too little, and scopes like the TDS700 Series (which at that time was their highend model) use somewhere around the 100kpts which is where FFT starts to become actually useful, but since these scopes are really old (close to 20 years) and their processing is very slow as well.

Honestly, if you want good FFT then you should have a look at a LeCroy scope. Even the now roughly 20 yrs old 9300 Series could use up to 6Mpts for FFT (although of course the processing is also slow by today's standard due to their age). But the later scopes (i.e. WaveRunner LT) have much faster processing, and with the EMM or WAVA option use the full available sample memory for FFT. They also show signal phase, which most scopes don't.

A Spectrum Analyzer is of course much better for analyzing the RF spectrum than any scope, but you do pay a lot for that. FFT in a good(!) scope however can often be more than good enough.

[nctnico]

According to the datasheet the SDS2000 uses 1024 points for FFT. The way it currently is is not very useful. But on the TDS744A I used to have FFT wasn't very useful either. For a decent graph it needed long memory (I think it could use around 30kpts max) and 30 to 50 averaging cycles.

[extide]

to me the biggest problem with modern DSO's is the lack of external clock sync and tools to time align with other acquisition tools.....that baffles me beyond any of the other potential "problems" with these tools...

Not sure what scopes you are looking at specifically, but only the very base low end scopes do not provide a 10Mhz ref in (sometimes out as well) and also a trigger output. Using these two connections should be sufficient to synchronize with other test gear.

[David Hess]

to me the biggest problem with modern DSO's is the lack of external clock sync and tools to time align with other acquisition tools.....that baffles me beyond any of the other potential "problems" with these tools...

Not sure what scopes you are looking at specifically, but only the very base low end scopes do not provide a 10Mhz ref in (sometimes out as well) and also a trigger output. Using these two connections should be sufficient to synchronize with other test gear.

He might be referring an external sample clock input.  I have a couple of old DSOs which support this.

As far as the trigger outputs on modern DSOs, they seem to have a lot of latency and/or jitter compared to older DSOs which use analog triggering.