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Appropriate Scope for vintage computer diagnosis

falter

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Hi guys,

A member here has very kindly offered me this scope for a very reasonable price:

http://imgur.com/a/NP1qg

It's a Leader LS-1020 20 mhz dual channel unit. I am wondering if it would be sufficient for helping diagnose these machines of mine? Most of my stuff is pretty old, but there are some 'new' ish units like my Amiga 1000 that need work and that I think only a scope could help on. Thoughts?

Thanks!!
 

Uniballer

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It depends on what you think you need to see. That scope can see a 20 MHz *sine wave*. It is unlikely to display something that looks like a square wave for anything over maybe 4 or 5 MHz. A working 20 MHz scope is certainly better than a logic probe, or voltmeter, for looking at changing signals. But I know I would want more bandwidth, and possibly signal storage.
 

KC9UDX

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I find a good logic probe more useful than a 100MHz scope.

Very seriously, every time I think I'm going to use a scope whilst working on a computer, I end up using my logic probe instead. The one I use has a very good Pulse function, and I have a really good feel for what it's doing.
 

Osgeld

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or a logic analyzer to watch multiple signals at once, there's some stupid cheap usb models on ebay which are not that great but for the price...

I use my 20 mhz scope all the time, but I do a lot of analog work
 

falter

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Thanks guys. My diagnostic skills at that level are limited and I'm not always clear on where a logic analyser/probe is better or not than a scope in certain situations. Some folks have said 'scope all the way' in the past.
 

KC9UDX

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Like Uniballer said, you really need a powerful scope to work on "slow" digital stuff. Digital is square waves, which are many, many overtones, octaves higher, than the analog equivalent sine wave.

A logic analyser is a whole different animal, and yes, you could use one of those more than either a logic probe or oscilloscope. I've never owned one, and I'm not sure if I ever used one. I do mostly analog work. But, when I work on computers, I've got this cheap, no-brand-name logic probe that I bought in 1994, which always gets the job done.

I've used other logic probes that don't work well for pulsed circuits. In fact, everyone I've used other than my own, I've found useless. I don't know where to get one like mine, I've tried to find another one. But, every time I get one that looks like it, it doesn't work as well.

I've never had trouble picking out pulsed signals at 20MHz. I often have to take multiple readings, and compare the audio tone to a logic high and logic low, but I always get an idea of what is happening on a circuit. It has a Pulse mode where it only chirps once when the logic state changes. So as the state goes from low to high it chirps, and when it goes from high to low it chirps again. And, it lights green and red LEDs to reflect the state. Based on the distinct modulated sound, and the apparent colour of the two LEDs alternating at high frequency, it's usually pretty easy to tell if a circuit is doing what it's supposed to.

Obviously, if you need to compare timing between two circuits, you need at the minimum an oscilloscope, but, more useful would be a logic analyser. I haven't looked at those lately, but I would assume the way things are today that they are affordable. If you can afford one, go that route instead of a scope, if you don't plan on doing a lot of analog work.

I've never found myself in a position where I absolutely had to compare two circuits at high speed. I'm not saying I never will, but I haven't so far.

Just recently, I went through a lot of trouble to set up my scope, to work on two Amiga 2000s. But, my very high quality 100MHz scope is pretty useless with a 7MHz clock. I ended up abandoning it and using my probe, as always. I've got a 200MHz scope that I probably would have had the same issue with.
 

billdeg

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I have been very happy with the Diligent Waveforms system, it's a USB device that uses your computer as the display. A lot of power and easy to use.
 

SpidersWeb

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I have a 20Mhz CRO dual channel, originally designed for TV repair.

It's good for detecting say a CAS and RAS signals on an XT, and letting you see the waveform (make sure there is no noise, check voltage etc). Also great in power supplies and CRTs.
However even a 4.77Mhz XT clock is a bit of a trick, to the point I barely see more information than I would with a logic probe. I've spent a lot of time getting frustrated with it.

So it'll depend on your budget, and what you plan to poke with it.

I plan on getting a new digital scope at some point - probably a Rigol DS1054Z with a firmware hack.
 

Uniballer

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A logic analyser is a whole different animal, and yes, you could use one of those more than either a logic probe or oscilloscope.

A logic analyzer can be a great tool. I have often found It was the best tool for working with prototype digital hardware, or for chasing firmware bugs. But the problem is that certain kinds of electronics problems need more resolution than "high" and "low". For example, I had a piece of equipment that was damaged in a lightning storm and one of the signal lines couldn't pull all the way "low" any more. A logic analyzer would have seen "high" all the time, A scope showed that the signal was changing, but not enough to register as "low". Swapping one component fixed it.

A decent scope is the most versatile troubleshooting tool other than your brain.
 

dave_m

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It's a Leader LS-1020 20 mhz dual channel unit. I am wondering if it would be sufficient for helping diagnose these machines of mine?

If it's offered for less than $50, go for it. If not, look for a Tektronix 454 or 465 on ebay for about $100. They have an 100 MHz bandwidth to see square waves of 20 MHz. Great for everything except a one time power up event. For that one would need a memo scope or perhaps a good logic analyzer.
 

KC9UDX

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If it's offered for less than $50, go for it. If not, look for a Tektronix 454 or 465 on ebay for about $100. They have an 100 MHz bandwidth to see square waves of 20 MHz. Great for everything except a one time power up event. For that one would need a memo scope or perhaps a good logic analyzer.

Yes! Don't ever pass up one of those scopes for $100! They are well worth it.

But get at least a cheap logic probe if you go that route. There is one other factor: operator fatigue. For most quick checks, hearing a sound, or seeing a light near where you're probing beats looking up at a scope and mentally converting a line position to a digital level.
 

gslick

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If you ever get down to the Seattle area from Vancouver and you decide you might want a classic old school but still very usable logic analyzer I have some HP 16500B mainframes and I could give you a decent deal on one. Too big and heavy to be worth the hassle and cost of shipping relative to their current market value.

-Glen
 

NeXT

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Sphere's having their annual free day in a week and a half. They probably won't have any scopes out that will be working and ready to go but they will have something in the range of what you are after. Last year I got a Tektronix 2445B for $50. Only downside is they are in Kelowna.
 
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