How risky is buying older analogue Tektronix scopes?

[Chris Wilson]

I have had some great advice as a newbie on this forum, for which I am very grateful. I have now decided that I would like a decent analogue scope as well as my digital. I have totally insufficient electronics experience to tackle a repair on a scope that proves faulty, or fails in service, and would either have to bin it, or pay for a pro to have a look at it. I have decided that it's false economy buying something just sufficient for my needs and it might be prudent to get something pretty capable that will see me out. I was thinking of a 2465 series or even the older 465 scopes. How risky is the purchase of a supposedly tested and working scope like this? Is it likely to be economically repairable if something more than the fuse blows, or do I look at them as throw away? I read of old electrolytics failing with gay abandon, and I am concerned I might just be buying a load of hassle. Are these older analogue scopes a fairly safe bet, as best as one can say? Thanks.

[PeteInTexas]

If you buy a used scope online, sight unseen as they say, then you definitely need to be prepared to "throw away" whatever money you've put in.  At the very least consider shipping cost gone and analog scopes tend to be on the heavy side.

What is more interesting is how you have come to conclude your present digital scope is now inadequate for you needs.

[saturation]

A reason used is a "good" deal is should anything go wrong, experienced buyers will use their own expertise and labor to do repairs, after purchase or in the future, as needed.  If a buyer doesn't count themselves among those types, it will be a risky buy to get used scopes.  Its hard to say how risky, because a lot depends too on the condition and age of the item.  Experienced folks know which gear to stay clear off because its difficult to repair or not worth owning even if working or repaired.

Lastly, a used item that is working when sold, could break anytime, after purchase.  They are all past their expected lives,  so a buyer should really expect failure to happen during its lifetime with the new owner.

[vtl]

Before you buy just make sure you see a picture of a trace, preferably the cal signal.

Teks are pretty reliable, even old ones so its not exactly a high risk thing. Old scopes will be using almost exclusively throughole construction and the service manuals are readily avaliable. They have full schematics and they almost always have the theory of operation explained in laymans terms.

Whats risky is buying broken scopes that don't show a trace. You have no idea if theres missing parts or bad repairs.

Most of the problems with old scopes will be from the power supply. Tantalums and electrolytics are the most common failures and not exactly hard to replace. You can quickly tell with a multimeter if any have failed short. Then you can go about looking at ripple in the rails if its still not working. Its not exactly hard and its a good way to learn if you're starting out.

[amateur_25]

Personally I would NEVER EVER buy another used scope unless I know everything there is to know so I can repair them. I too didn't want to spend 300 quid on a scope.
I got one off ebay. By the time it arrived the crt tube (the screen has a very fragile glass tube that's why the scope is so big) was smashed. It was load of hassle which involved reporting it to ebay so I could get a refund. I know this because I could hear glass moving around inside. AFAIK the crt tube is the only thing that's made of glass.

[gregariz]

You can still buy a new analogue scope although they will be more pricey than an equivalent digital scope. Something like the following looks reasonable

http://www.circuitspecialists.com/os-5100rb.html

[ModemHead]

If you want a used Tek scope and you don't feel qualified to do a repair job, I think it would be best to buy from an experienced scope refurbisher. They're not hard to pick out of the eBay listings, because the price will be higher, and the listing will show a number of pictures of the scope displaying test signals. Probes and manuals on CD-ROM are often included by those sellers. Unfortunately, the cost will probably approach or even exceed the cost of a brand-new hobbyist-level imported DSO.

I recently won a dead 465 on eBay for cheap, as a fun project. It turned out to be an easy repair (didn't involve capacitors at all though, surprisingly.) Almost all discrete transistor circuitry, and every transistor is socketed. If the CRT holds out, I would expect this thing to outlive me...

[alm]

Lastly, a used item that is working when sold, could break anytime, after purchase.  They are all past their expected lives,  so a buyer should really expect failure to happen during its lifetime with the new owner.

This statement is true for any piece of equipment. New equipment may have warranty, but sending it to the other side of the world may be expensive and take a lot of time. The old equipment has had a long burn-in period, so any weak parts will have died by now. Whether failure within the next few years is more or less likely than a new piece of equipment build from the cheapest components is not immediately obvious.

[saturation]

Today's components may not be made with the same quality as the 1990s and before, but the biggest question is does time still play a big role in estimating reliability? So far, industry still follows the standard reliability index, MIL-HDBK-217, where time is a key factor.  You can use this website to punch in your operating conditions and calculate MTTF rather than using the handbook to do it by hand:

http://www.sqconline.com/military-handbook-mil-hdbk-217-beta

Components wear via different mechanisms, but as components rely on each other, a non-fatal failure in one cascades to others leading to failures in areas made with otherwise more reliable parts, called "root cause."  So, the probability of entire systems failing also increase as more parts are used, as in older style discrete design.

http://www.ece.cmu.edu/~koopman/des_s99/electronic_electrical/#ers87

http://en.wikipedia.org/wiki/Failure_modes_of_electronics

http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/40791/1/08-05.pdf

Time tends to reveal weak spots in a particular design, such as a phenomenon not considered a flaw in the past,  a true known manufacturer's defect, or one that is know to wear, such as electrolytics.  Among Tek scopes, there are examples of this on eevblog, such as the U800 chip failure on 24xx series.  A list of more items appear here:

http://www.sphere.bc.ca/test/tek-parts/tek-info.html 

The idea I brought up is reflected in the bathtub curve, which is a simple model for electronics reliability.  Reliability is an entire field in itself, so this post is best left an introduction with links above for those interested in knowing more:



So in the end, if you buy a used scope, the final question is, is probability on your side and can you risk it?  I think anyone who can repair will say yes, but one who can't will be faced with a true boat anchor.

Lastly, a used item that is working when sold, could break anytime, after purchase.  They are all past their expected lives,  so a buyer should really expect failure to happen during its lifetime with the new owner.

This statement is true for any piece of equipment. New equipment may have warranty, but sending it to the other side of the world may be expensive and take a lot of time. The old equipment has had a long burn-in period, so any weak parts will have died by now. Whether failure within the next few years is more or less likely than a new piece of equipment build from the cheapest components is not immediately obvious.

[Chris Wilson]

If you buy a used scope online, sight unseen as they say, then you definitely need to be prepared to "throw away" whatever money you've put in.  At the very least consider shipping cost gone and analog scopes tend to be on the heavy side.

What is more interesting is how you have come to conclude your present digital scope is now inadequate for you needs.

It's not that it's inadequate, it's that it's a USB scope and it drives me crazy. I don't like working on laptop keyboards to control a third party instrument. However, for my car diagnostics it is very useful, as it's portable and will use roll mode, or of course, store signals. I much prefer "proper" knobs and buttons, and I want to learn more about using scopes in general and am thinking of taking up amateur radio as an evening hobby later this year, and maybe building some fairly simple gear myself.  There is something tactile about these older quality analogue scopes and as they are now relatively cheap to buy I fancy having a play with one, to be honest. 75% I just fancy having one, 25% I would like to learn to use one properly I have just been told about a UK supplier who warrants used older Tek scopes, and who is apparently well respected over here. His prices are a little over and above Ebay prices, but dealing with a supplier who gives some sort of warranty, and where I can visit and see the actual machine working would be a bonus that's probably worth the extra cost to me. I guess the USB scope is like having a modern home, it's efficient, simple and easy to live with and maintain, but it's not a Victorian house with more build quality in the bannisters and fireplaces than the whole of a modern place. The Victorian may be hard to heat, a little likely to have "issues" from time to time, but not withstanding, it's a thing of craftsmanship and some would say beauty, and a nice thing to own. I think I have got to "that age" where sometimes you appreciate older technology and build quality, and want to experience it just for the sake of it It's a poor reason I know, but it's an honest answer! It'll keep me out of the pub a bit, too, which, given UK taxes on alcohol, will probably pay for the scope in short order

[Rerouter]

as a man who recently was gifted a broken 475 and repaired, i have to agree with vtl, just about all the discrete logic is in sockets, transistors included, and generally only have an electro or a tantalum die, an the electronics is very robust in the things, (accidentally shorted out 2 voltage rails while repairing and suffered no damage)

however i also am aware of just how hard it gets if the tube is damaged, or one of the custom IC's gets damaged (rare for the ics)

in short, if you want a good old tek analog, look into the 465 475 or 475A, and if you want something more modern, the 2000 series, but i'm not too sure on them myself, as i haven't played with anything higher than a 475A

[PeteInTexas]

If you buy a used scope online, sight unseen as they say, then you definitely need to be prepared to "throw away" whatever money you've put in.  At the very least consider shipping cost gone and analog scopes tend to be on the heavy side.

What is more interesting is how you have come to conclude your present digital scope is now inadequate for you needs.

It's not that it's inadequate, it's that it's a USB scope and it drives me crazy. I don't like working on laptop keyboards to control a third party instrument. However, for my car diagnostics it is very useful, as it's portable and will use roll mode, or of course, store signals. I much prefer "proper" knobs and buttons, and I want to learn more about using scopes in general and am thinking of taking up amateur radio as an evening hobby later this year...

Oh god yes, anything is better than a USB scope even if the specs match.  I completely agree with proper knobs and buttons.  That alone is worth the extra money to me.  I like being able to glance at a knob/lever/button and know what the setting is instead of navigating a menu to find out or its some color coded hieroglyphic crowded onto the screen.

As far as having an analog scope just to have one to learn about them, the best thing at this point is likely to find someone nearby to show you theirs.  When you get into amateur radio,  find a local club.  I'm sure there will be fellow enthusiasts more than happy to show you what they have and from that you can have a better idea on finding good deals ebay.

[vk6zgo]

Lots of people buy secondhand Tek & HP Oscilloscopes with no major problems.
The capacitor problem is very overrated,as well designed equipment can tolerate a lot of electrolytic cap aging before it causes major upset.
Total failure is far less common than the failure of one channel,or sometimes,triggering faults.
If you do encounter a fault,you are not totally helpless,as you can use your cruddy USB scope to fault find in the Tek.
You usually need a 'scope to fix a 'scope,although it can be done with a  DMM with a lot more difficulty.

VK6ZGO

[Kilroy]

The capacitor problem is very overrated,as well designed equipment can tolerate a lot of electrolytic cap aging before it causes major upset.

I'd have to agree.

I know it's only one man's experience, but I have yet to  replace a single capacitor in all of the decades old test equipment I own.  Much of it is HP stuff (scopes, generators, counters and such) possibly older than many of the folks that participate in this forum.  If I amortize the original purchase cost of this equipment over the number of years of trouble free service it has given me I have spent a relative pittance for it.

Anyway, life's short...I'd say go ahead and get your analog scope...in fact, while your on about it, why not get several.

[nrgeek]

I just bought my first scope a tek 465m .. pics shown had trace.. and was clean .. I didn't have the money to plop down 400 for a rigol .. 100 us dollars was my limit with shipping .. I spent almost a month bidding on scopes before I finally won a scope at auction .. kept getting sniped !@$!^$@!
ok so it arrives.. I plug it in and it works .. I take over to a friends that knows them inside and out .. he tested too .. checked calibration .. was perfect - spot on! 
So $85 us dollars that included shipping was great.. and I would buy another in a heart beat.

One thing to think about .. is the probe cost as well .. few of the ebay scopes I saw came with probes .. as most where surplus from closed factories, military etc

Good luck with which ever route you decide to go

[FenderBender]

I also just purchased a 465m off eBay. $80 shipped. (Perhaps it was the same seller? I got it from some guy in Canada).

I have a teardown of it somewhere in the product reviews section. Though it is a very old piece of equipment, I don't necessarily see any sudden death in the near future. There's really only a few things that could go wrong with these scopes.

Here's my list. Almost all of these problems are fixable-

1.) Power supply- Electrolytic caps gone kaput
2.) CRT burns out
3.) Switches, potentiometers wear out
4.) ICs die

Replacing caps is easy shmeezy, Can't fix the CRT, but there are lots of people selling old ones, and even some new old stock. Some of switches are proprietary 'Tek specialties', but with some isopropyl alcohol and a little bit of creativity, you can get any dirty switch back up and..switching. Potentiometers are almost always standard types. Sometimes they are on funny standoffs from the board, and you might have to fit a extender rod onto it, but it's do-able. And you might think "OMG an IC burn out, I'm screwed!" But alas, Tek sockets just about every DIP IC, and even some transistors if they feel like it. Plus the parts themselves are typically standard logic type parts. There are some Tek chips but typically you can find replacements. Only thing you really don't want to mess around is the HV section unless you really know what you are doing.

My scope works well; The only complaint I have is that some of the pots and switches are a little sticky or gritty. So I might try replacing some of the more prominent pots and maybe a switch or two.

Remember, these scopes are not like the stuff you see today. They were built like tanks.You can take almost any MTTF and throw it out the window, in my opinion. I'm not saying that these things won't fail, because everything will fail at one point or another, but it is highly unlikely that anything catastrophic happens, and even if it did, you could probably fix it.