How to use an old-school oscilloscope

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How to use an old-school oscilloscope, to repair now-vintage computers

In early May 2024, someone asked in a vintage-computer discussion group, something like this. "I bought a new inexpensive digital oscillscope, to repair old computers. But I don't have broken computers to start with. And I'm unfamilar with use of oscillscopes. Where do I start that isn't complicated? I really want to learn how to fix old computers, for the reward of bringing them back to life. "

Maybe they were asking for vintage computers? ;) but I like to think, they were asking how to use an oscilloscope to repair computers - just stuck on how to proceed. The responses they got, included "get a how-to-use-an-oscillosope kit", "calibrate your scope, read the manual, learn its features", "buy some 8-bit microprocessor kit, learn from that", "try an old battery radio", "go to a hackerspace or vintage workshop, learn from other people".

Well, I have responses to some of these things. I posted something like the response below, which I'll edit as I see other responses. I've used a lot of test equipment myself, and have some available. - Herb Johnson

How to use an oscilloscope?

How to use an oscilloscope, is a tough question now in 2024. It's an experience few people have today, that might have an interest in how some computer-thing works when broken (or not). So why do some people make it *hard*? ;)

old-school vs today

Traditional responses to "how to use an oscilloscope", is 1) to learn the instrument thoroughly, 2) be sure it's accurate 3) use it for designated purposes like research, repair. 4) oops, better learn digital logic and microprocessor signals too. (whoa, that's so complicated).

That's because, computers and oscilloscopes were once expensive things, used by people with detailed knowledge of signals they show and how those signals are produced, and why. That's college-level tech, from the days of simple computers and simple electronics. That's my era.

But oscilloscopes now, are just a thing like other electronic things. Old and cheap, new and cheap, buy and try and figure it out. So, I don't think the old-school approach is gonna work. So here's my old-guy approach with try-it in mind.

try-it strategy

You bought a 'scope. OK. Grab anything you have that has a circuit board that's battery powered. Figure out where "ground" is, clip the ground lead there. Now use your scope probe, put it on parts of the circuit. Wadda see on the scope?

However: learn what it means to "ground" things and avoid "AC shocks". That's why I suggest battery-powered stuff first.

If you don't see anything on your scope, look through whatever oscilloscope manual you can find. The manual for your scope will help BUT it's like "here's how all the knobs work" and not too useful for "why do that?". But look for advice and how-tos. It would not hurt to find old "how to use your oscilloscope books", but there are PDF's of those.

Also, find some info on whatever you are probing. Know what a schematic is? You'll find out! Hope you find some for whatever you are messing with.

Do that awhile, on different things. Read, test, probe. Now you have experience. Get more information based on what you KNOW now, and then what you want to know.

Try, fix specifics: new computers, old

If you want to repair something in particular (computers)? Grab one, any thrift store, your friend's closets and attics, whatever local. Or USB hubs or routers. *DOn't mess with CRT monitors or LCD's or TV's yet. YOu could hurt yourself seriously. Please avoid for now.* Look inside. Now what?

The chips are small, the leads smaller, and nobody tells you (or me) what those signals and chips mean. It's a dead end (for most of us) to use an oscilloscope on modern computers. Same applies for Arduinos and Rasp Pi's, other than looking at signals your program produces, where you know (or should) what signals look like and why. This is not your fault.

The old 8-bit computers? The simplest old/new vintage computers are little single-boards based on 8-bit processors like those in the C128, Apple II, and other 1980 computers. There's lots of sub-$100 kits for those, today, if you like building kits. The old processor data sheets, describe the signals. Look them up, to get some clues. They use "big" chips, big pins, not the little "surface mount" chips on today's devices, too small to poke at.

You'll break things, using your oscilloscope. Everyone does.

See, you are learning stuff already, just reading this. I hope!

vintage homework

Still, at some point, you'll have to do some homework on how vintage computers work at the chip IC level. That's what the oscilloscope tells you about. It's not your fault or the oscilloscope's. that's what it's supposed to do, the computers do what they are supposed to do. If the computer fails and some signals fail - how would you know failed from good signals? You gotta do your homework eventually.

Plan B: pre-computer logic and analog

Plan B if "all this stuff is too hard"? Well, that "how to use an oscilloscope kit" amounts to a AC to DC power supply running a "five fifty five" or 555 chip oscillator/timer. That's a very famous chip, whole books (not hard to read) about them. Simpler than a processor!

A person, Forrest Mims, is an old guy who built simple circuits years ago, to do *real things*. He's done that for half a century! He's actually important for doing that. His early circuits, are still simple, still buildable. Look up his old how-to books, notebooks, scrapbooks, etc. See what you can do with simple circuits. Gotta start somewhere with circuits!

You used to be able to buy breadboard "build 99 circuits" kits with power and a breadboard ready for use - then put chips in it, hook up wires to do things. that's a great learning opportunity. Check Ebay for those old breadboards, repairing them is fun too. JHere's what I'm talking about. There's probably modern versions of these breadboards too.

where to buy kits

There's several "hackerspace" type companies that still sell learning how-to electronic kits. Adafruit, Sparkfun, are among them. Some of those kits, use non-microprocessor "analog ICs" or "digital IC's". Try some of those things. It's all online now of course, no local shops. There's Amazon & Ebay for cheap "import" stuff, but it's not organized, and the sellers don't offere supporting information or back them up with discussions, etc. Individual persons, have kit companies too, check them out. Here's two I have worke with:

ancient, cheap COSMAC 1802
ancient Intel 8085 kit, not expensive

There's actual hackerspaces, look for those near you if you are social and mobile. But the thing is, visiting them with no knowledge is kind of intimidating. Some shops have beginner's days. Or go just to watch, not bug people with questions. Figure out the social scheme of the shop.


But keep "your eyes on the prize". Your goal is to read signals on electronics to perform repairs. The oscilloscope is your eyes. The electronics, are the target for knowledge or repair. All this other stuff are means to that end.

It's all a process. It takes time, attention, desire and interest. It's a real thing, not a ten-minute thing, that's how such things go. That's the world that an oscilloscope can explore, but you point the probe not the oscilloscope, so you gotta know. - Regards Herb Johnson

Herb Johnson
New Jersey, USA
here's how to email @ me and to order

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