[vcf-midatlantic] Old computer I can learn to repair?

Sat May 4 21:13:55 UTC 2024

I think the scope of my original question was far too vague & made me sound
more of a beginner than perhaps I actually am.  Please don't take any of
this as a dismissal of some really awesome advice.

I've already figured out generally how the scope works.  I've watched a
serial signal do serial things. I've looked at audio output make "waves".
I've looked at composite video signals to identify the wave form (thank
Neil Cherry for teaching me about that!). I've calibrated & tested some of
the settings with the signal generator, etc.  I've also repaired computers,
monitors & other sundry electronics over the years but mostly out of
trial/error, luck & brute force (aka, keep replacing parts I think might be
bad until it works).  I've just outgrown using (just) a multimeter but
haven't graduated to the point I can justify something more expensive than
this Zoyi scope yet.  Forrest Mims is great & I recently bought one of his
books that I had as a kid so I definitely know who he is.

What I don't have is formal electrical engineering training of any sort but
I can follow the lines & symbols on a schematic to varying degrees of
success.  I can follow along with Adrian Black as he fixes various
computers & generally understand what he's talking about.  I bought the
scope because I wanted to not just watch Adrian Black do his thing but
actually do it myself.  I've just had the "unfortunate luck" of having all
working computers.  Looking at various signals, etc. is cool & all but
fixing things is where the real fun is at.  I learn best by doing & working
a real problem does a much better job holding my interest than just
academic observations, etc.

I just put this out here because I know there's lots of people here with
old computer stuff who I'd much rather interact with than Facebook
Marketplace, et al.  I've met a number of you at repair days & VCF, etc.
Anyhow, sorry if my initial question was misleading.  I'm definitely an
amature & my skills are still fairly basic.  I 100% appreciate ALL the
advice & any other guidance you all are willing to give.  Hopefully makes
more sense now.

On Sat, May 4, 2024 at 3:52 PM Herbert Johnson via vcf-midatlantic <
vcf-midatlantic at lists.vcfed.org> wrote:

> Caution: lecture. Reading time long, skip if impatient. a real question
> was asked. Sorry.
>
> 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*? ;)
>
> 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.
>
> YOu bought a 'scope. 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.
>
> 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.
>
> See, you are learning stuff already, just reading this. I hope!
>
> 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.
>
> YOu'll break things, using your oscilloscope. Everyone does.
>
> 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 builds simple circuits, to do
> *real things*. He's done that for half a century! He's actually
> important for doing that. His circuits, are still simple. Look them up,
> see what you can do with computers or without, using 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.
>
> https://www.retrotechnology.com/restore/breadbd.html
>
> There's several "hackerspace" type companies that still sell learning
> how-to electronic kits, some that 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 actual hackerspaces, look for those near you if you are social
> and mobile. But the thing is, going 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.
>
> 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.
>
> I said, this was a real question.
>
> Regards Herb Johnson
>
> --
> Herbert R. Johnson, New Jersey USA
> https://www.retrotechnology.com OR .net
> preserve, recover, restore 1970's computing
> email: hjohnson AT retrotechnology DOT com
> or try later herbjohnson AT comcast DOT net
>

-- 
- Benjamin Krein