How repairable are "average" 1990s oscilloscopes ?

[lordvader88]

By average I just mean a typical used/broken 1990s scope. It seems most pre-1980s scopes have full service manuals available, and enough jellybean parts so that a repair might be possible.

What about the 1990's ? Are many service manuals available? Did they use way way more custom and obscure chips that can only be found now in other used scopes ?

[tggzzz]

It  will greatly depend on the fault. Bad PSU caps are as repairable as in any other piece of equipment. Bad custom ICs require a parts mule or luck on fleabay.

More to the point if it is a 1990s digitising scope, why bother? They were uniformly much less usable that 1980s analogue scopes. It is only in the past decade that they have become pretty usable.

[SilverSolder]

"if it is a 1990s digitising scope, why bother?"

Dave did a review on the 54622D which, green screen and all, is a pretty good MSO for hobby use.  They can be found for not much money and are probably more useful overall than an 80's scope of the same bandwidth.

As for being repairable...   unfortunately, by that time, we were entering into the era where publishing circuit diagrams was considered unnecessary.   The stock market could only go up,  we were all going to be billionaires able to afford new scopes every 3 months, on subscription!

[bd139]

You can get circuit diagrams for the earlier HP branded 546xx scopes.

I like the 90s Tek TDS2xx series. Seem to be able to get the bits for nothing and there’s not a lot inside them to go wrong! Here’s a TdS210 I did:

https://www.eevblog.com/forum/testgear/tektronix-tds210-teardown-and-bnc-replacement/

[Hexley]

One thing to check is whether a particular scope that you are considering stores calibration data in a Dallas Semiconductor battery-backed SRAM. The batteries in those are coming to the end of their lifetimes, and replacement of the chip can be a problem if the original part has been discontinued. Something to keep in mind when you are choosing what to buy.

[shakalnokturn]

Hexley has a good point.

If you are consideting the investment for a first DSO, search what service information is available  before buying.
On the whole I'd say they are quite reliable and serviceable as long as you don't run in to GAL/ASIC trouble,  you must consider going through a full checkup when you buy one just as a preventive maintenance approach.

I favour the Tek TDS500 and LeCroy 9300 series as they still have reasonable specs. and some service information.
The NVRAM  can be a problem for the TDS.

[Rasz]

"if it is a 1990s digitising scope, why bother?"

Dave did a review on the 54622D

its post 2000 scope, plus you get 15-18 year old gear at a price point and features of brand new Rigols

[lordvader88]

1 of these days I'd like to get some broken 90s style 1GHz scope for fun, they still cost too much most of the time if they are working. But I certainly won't get 1 without a schematic and lots of other repair threads/videos on it.

[joeqsmith]

Given enough resource, I suspect most things could be repaired.  The time or money involved may make it not viable.   I gave away an old Tek DSO that had been given to me because I could not find parts for it and the scope was nothing special enough to where I wanted to try to hunt down another to scavenge for the custom parts. 

A friend of mine recently sent me an old LeCroy DSO.  I had happened to have this same scope at one time that I had given away.  I still had some parts for it so I took a few days trying to revive this one.  Not the best use of my time but beats cleaning out the gutters.   

https://youtu.be/WXFoAAL7hxo

https://youtu.be/7SByDsNaYiA

[G0HZU]

More to the point if it is a 1990s digitising scope, why bother? They were uniformly much less usable that 1980s analogue scopes. It is only in the past decade that they have become pretty usable.

I've just upgraded my 1990s digitising scope....   ... with another 1990s digitising scope 

I salvaged an old HP Infiniium scope from the company dumpster today. It's nearly as old as my HP54540C DSO and is running Windows 98. It doesn't have a model number on the front but I think it is a HP 54825A 2Gsa/s 500MHz with 4 channels. I've only just got it home and switched it on but seems to work OK but was dumped because it wouldn't boot up. But whoever wrote it off didn't try fitting a keyboard. With a keyboard it boots and runs like new

It doesn't have much sample memory though. I think it has just 32k but I think this scope is quite useable. It's certainly prettier and more intuitive to use (and quieter!) than the HP 54540C it is dislodging on my workbench

[David Hess]

1990 is about when they stopped including full service documentation.  On the Tektronix side, the 24xx series analog and digital storage and four channel 22xx series analog were the last ones with full service documentation.  The follow on 11k and TDA/TDS series lack full service documentation.

[ebastler]

What about the 1990's ? Are many service manuals available? Did they use way way more custom and obscure chips that can only be found now in other used scopes ?

I am not sure how meaningful this is as a general question, independent of brand and model.

If I had my eyes on a particular scope (which someone might be offering to me, or which looks tempting on ebay), I would search the internet whether a service manual is available for that scope. Maybe discussions about typical faults and their repair are also to be found online. Then base a purchasing decision on that model-specific information.

[Johnny10]

I have had a number of 1990's scopes and I can attest to the difficulty finding any service data on 11000 series and later.
Makes it very difficult to repair those scopes.
A couple of times I have been lucky enough to find donor units to aid in repair.

I have two of every 1990s scope I own just for comparison or for parts.

[james_s]

I have a few early-mid 90s DSOs, they work fine. I have a nice analog scope too but I almost always grab the DSO unless I need XY mode.

[bd139]

XY mode on the early TDS LCD units is quite good.

[james_s]

My scopes are all CRT based. I've yet to use a DSO that has XY mode even close to as good as analog. It might work for basic stuff but not for displaying the output of a vector game board.

[drussell]

One thing to check is whether a particular scope that you are considering stores calibration data in a Dallas Semiconductor battery-backed SRAM. The batteries in those are coming to the end of their lifetimes, and replacement of the chip can be a problem if the original part has been discontinued. Something to keep in mind when you are choosing what to buy.

Are there ones that are commonly used in scopes that are not available anymore?  I thought it was basically just the ones with the internal RTCs that weren't being made anymore.  Regular battery backed DIP SRAM modules are still available in the common configurations like 2/8/32/128/256/512K x 8 bit.

They're not exactly cheap, but those Dallas modules have never really been inexpensive. 

[james_s]

Many of the Tek DSOs use Dallas SRAMs with RTC, those are harder to find and quite expensive. It's not too hard to cut the battery out and solder in an external one though.