"Retro Repair" key electronics skills?

dwight dkelvey at hotmail.com
Tue May 10 17:09:57 CDT 2016

In order to trouble shoot, one needs to know how it is suppose
to work. This often means studying schematics, data sheets and
sometimes even app-notes.
Avoid the replacing everything, until it starts working, type trouble
shooting. As well as being a waste of time, it is more likely that
you will introduce new problems in the process.
Don't replace a part unless you can prove it to yourself that it is
the most likely source of the error. This usually means running
experiments. Since you are a coder, I find that anything with a working
processor can be used as a self debugging tool. EPROMs or
front panels are great for trouble shooting. Simple test are best.
Many fear power supplies. Linears are the easiest because they
are always some form of feedback loop. You just follow the loop
until you find two points that are opposite directions from where the
input point predicts the output point should be( goes back to knowing how
it should work).
If you can't find a schematic on the web, draw one. As a minimum, have
a block diagram.
I'm sure you have heard of the "scientific method". Trouble shooting is
just that. It is the repetitive process of making an educated guess as
to the source of the problem and then having an experiment to
prove it either true or false. Try to have experiments that are conclusive.
This is why I don't much care for the piggy back RAM test.
It may or may not tell you that there is a problem with the RAM that
you are checking.
Learn to use a two channel oscilloscope with trigger and delayed

From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Swift Griggs <swiftgriggs at gmail.com>
Sent: Tuesday, May 10, 2016 1:03:44 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: RE: "Retro Repair" key electronics skills?

On Tue, 10 May 2016, tony duell wrote:
> It's a very real problem, it's the main reason for decoupling capacitors
> which provide a local source of power with a low impedance connection
> (as they are so close to the IC).

It seems like there is a lot of "fiddling" with those types issues and
getting good at doing so is part of the process of getting profecient with
component level troubleshooting. That's why working with electronics
"kits" (ie.. kit based projects) is about my speed right now. In most of
those cases, folks have worked out the kinks involving connection issues,
but I'm still just doing analog stuff. I have no idea how much it'll
matter when I go to learn a bit about digital. However, that quote about
digital circuits being made from analog physical bits seems like good
foreshadowing. So, we'll see.

I'm still playing along with projects from a kids' Elenco kit. I'm having
fun with timers and making "bleeps and bloops". I'm also using it to try
and figure out how about 5% of my borrowed ocilliscope works. I've got the
manual, it's just figuring out what everything means is a bit challenging
right now. So, it helps teach me how to calibrate the darn thing to just
sit on something that looks like a sine wave etc...


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