How useful can an Oscilloscope be without a schematic? - Page 1
Forum section: electronics / beginners

author: Joedag90
author_rank: Newbie
timestamp: December 10, 2015, 02:47:59 pm
content: Hey everyone! So, I just got started building a few simple circuits and found myself wanting to see much, much more than just a blinking led or the parts required to make sound come from a speaker. After spending some time looking around, I have decided that a oscilloscope is the right tool (specifically the Rigol DS1054z). However, I have read on a few forums that an oscilloscope really isn't that helpful without a schematic of the machine you are repairing or without knowing the proper waveform ahead of time (I'm guessing it would be in the schematic?). I'm sure many newer electronics for repair can be difficult to get the schematics for since they are generally not expected (or wanted) by the companies to be serviced at home.Soo, long story short... Is an oscilloscope a worthwhile investment in learning even without a schematics book for the equipment you are fixing? Will I learn what is correct just by probing around functioning circuits? Is there a site or book where they have "standard" curves to compare to? I've seen many youtube videos on how to use an oscilloscope but not I don't remember any where they explain how to diagnose problems with one.I don't want to make the purchase a realize that without schematics or voltage values for the circuits i'm dead in the water.Thank you!

author: Deathwish
author_rank: Unknown
timestamp: December 10, 2015, 03:01:36 pm
content: Of course it is, you may not have a schematic for the precise kit you are trying to fix but one from a similar model will ( if included ) give you waveforms to look for or if you have experience of what you are repairing your memory will.

author: Lightages
author_rank: Unknown
timestamp: December 10, 2015, 03:07:03 pm
content: A schematic is the best thing to have to troubleshoot, but it is not necessary. As you gain experience you will be able to follow some circuits without a schematic just from the common way things work. There are also a number of videos online on how to troubleshoot and many showing specific repairs on many different types of equipment. These can help you learn generally and also help you repair the thing you have if you have the same thing.

author: madires
author_rank: Super Contributor
timestamp: December 10, 2015, 03:10:30 pm
content: Having the schematics or a service manual is very helpful, but you can fix things without them too. The classic approach is to follow a signal through all stages to find which stage causes the trouble. I think, experience will be the best teacher. I'd suggest to build simple (low power) circuits, scope them, remove or short a component and check what happens. A scope is a very useful tool in any case. And don't forget to watch some scope tutorials on youtube, especially about grounding (how to not blow up your scope).

author: Ian.M
author_rank: Super Contributor
timestamp: December 10, 2015, 03:24:31 pm
content: How useful is a <insert test equipment here> without a schematic?It doesn't matter whether the test equipment is a scope, multimeter, frequency counter, signal generator, or PSU; in all cases you need to have a reasonably good idea what to expect at that point in the circuit for your reading to be meaningful or to avoid damage. That means you have to understand the operation of that section of the circuit, to the point of reverse engineering it far enough to be able to sketch a schematic for the stage if you don't recognise it as a standard configuration for its application, and if you are unfamiliar with the active components, obtaining and studying their datasheets till you are able to determine the expected signal, its level and the DC operating point. If you don't understand the theory of operation of the general type of equipment you are working on, you are S.O.L. and will be reduced to witch-hunting for blown parts or dry joints, which rarely goes well as if you find a fault, you have no idea what else may have been damaged so your repair is likely to fail again sooner rather than later.

author: deephaven
author_rank: Frequent Contributor
timestamp: December 10, 2015, 03:55:00 pm
content: An oscilloscope is the most useful piece of test equipment you can have, with or without a schematic. It's your eyes into what the electronics is doing.

author: Seekonk
author_rank: Super Contributor
timestamp: December 10, 2015, 04:53:16 pm
content: In college I repaired audio equipment. Every week I would get some clown in the shop telling me he would fix it himself but he didn't have a scope. I hardly ever used one.

author: madires
author_rank: Super Contributor
timestamp: December 10, 2015, 05:03:17 pm
content: Quote from: Seekonk on December 10, 2015, 04:53:16 pmI find a scope very useful when adjusting the transistor bias of an amp. I don't have golden ears, but I can see any signal distortion on the scope easily when feeding the amp with a sinusoidal signal.

author: Shock
author_rank: Super Contributor
timestamp: December 10, 2015, 05:50:59 pm
content: Got to have the skills and the tools and the knowledge. Schematic will show you what can be time consuming to trace out, plus flow diagram, same as parts lists.Think of schematics as lots of small circuits, which familiarity, theory and experimentation will allow you to understand. Think of the math (calculating ohms law, algebra and so forth) as predicting how those small circuits should behave, think of the test equipment as how to confirm your predictions are correct. That is repair in a nutshell right there.Don't buy into all this scope magic though, owning a tool doesn't make you an expert, especially if you are on day one. Learn how to use a multimeter and a soldering iron etc, people will make you feel like you are not worthy if you don't have xyz gear. Make a priorities list.What you need is either some books and read them, design something and learn from the practical experience, assemble some kits and learn the theory of operation.

author: KL27x
author_rank: Super Contributor
timestamp: December 10, 2015, 07:10:58 pm
content: QuoteThat's a good way to look at it.If you have a live circuit that has unknown schematic or maybe unmarked or known parts, there are a lot of things you could do to "see" what's happening on any particular net/trace/pin.1. DMM voltage test? Good for seeing if you have a voltage, anyway.2. LED and a resistor? This can show you if this voltage is pulsing, at least. Up through maybe 30-50 Hz before you would have no clue if the signal is pulsing, at all.3. A variety of piezo speakers can take you from maybe 1 kHz through a could hundred Hz? You could at least know there's some pulsing.An oscilloscope will show you all of that stuff and on up through hundreds of MHz. So if you have no clue when you start, the oscilloscope can save you a lot of time when looking around. A twist of a knob or two versus rigging up various tests just to see if a pin is jigging or jagging. When you see the signals on a component, you can figure what it is and/or what it is doing. That's a pretty big help to figuring out a circuit and what is broken. Or how and where you might be able to tweak or modify the circuit to serve your own particular purposes.I have come to look at it this way:Poking around a circuit that is unplugged, you will get a lot of mileage out of your DMM for1. Continuity test2. Resistance3. diode checkOn a live circuit, the DMM is pretty useless. It can show you power draw... which you might be getting from your lab supply, already. It can show you more accurate voltages, when they're steady. Your DMM might even do frequency and duty cycle. But your digital scope will do that, too. Even where you think you know what's up with a DMM voltage meter, you sometimes can't be sure without seeing it on a scope. It's an instant sanity check in a process that can be very complicated, already. Better to be able to see it now than to earmark another one of many wild guesess or hedged bets you will be making along the way in figuring out what you're dealing with. The faster and easier it is to probe between different pins, the more likely you will be able to get a glimpse of the bigger picture to where something connects in your head. Without it, you may even forget what you have previously learned about the circuit at the time where that piece of information would be important.

author: fivefish
author_rank: Frequent Contributor
timestamp: December 10, 2015, 07:27:22 pm
content: QuoteI think a book will be a more worthwhile investment for you at this point. A scope isn't a magic box that will tell you what's wrong in a circuit with a screen readout.While a scope may be useful in repairing, it's NOT necessary in most cases. A working DMM, keen eyesight, good sense of smell, deductive reasoning, and basic troubleshooting skills sometimes is all that is needed.If you're calibrating something and the calibration procedure calls for a scope to measure a frequency, or period, then yes you need one for that calibration process.If you're designing a new circuit, yes, a scope is necessary to check for signal integrity, oscillations, timings, etc.

author: JaseG
author_rank: Contributor
timestamp: December 10, 2015, 09:53:51 pm
content: I'm a noob with a scope and I've found that it has helped explain a lot of things and continue my learning process.With a circuit, schematic and a scope I've been able to learn how the different components work under different conditions. I'd imagine that once you have a good idea of how components work, the scope would help you with reverse engineering things to build the schematic yourself. Dave does a lot of that in his videos aka DaveCad(tm)

author: wraper
author_rank: Unknown
timestamp: December 10, 2015, 10:04:17 pm
content: Quote from: fivefish on December 10, 2015, 07:27:22 pmMultimeter is sufficient in simple cases but very often lack of the oscilloscope makes a repair very hard or almost impossible to do and tenfold the amount of soldering (and spare parts spent) needed to find a faulty part. For example, just checking if there is generation on the quartz crystal can be a very big deal.

author: Seekonk
author_rank: Super Contributor
timestamp: December 10, 2015, 10:07:47 pm
content: Quote from: madires on December 10, 2015, 05:03:17 pmThat is what I have a Sound Technology 1702A for. Even someone with a tin ear can hear distortion before you see it on a scope.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: December 10, 2015, 10:48:04 pm
content: Whatcha plannin on fixin?

author: alsetalokin4017
author_rank: Super Contributor
timestamp: December 11, 2015, 03:53:20 am
content: You need: eyeballs+brain, a trusty DMM, and an oscilloscope.It is nice to have: the Internet, the schematic, a Function Generator.You can't do much without: a quality soldering iron, screwdriver set, fine diagonal snippers, a wire stripper.

author: pickle9000
author_rank: Super Contributor
timestamp: December 11, 2015, 04:56:34 am
content: Get the scope, learn how to use it, have fun.

author: highlux
author_rank: Contributor
timestamp: December 11, 2015, 05:39:18 am
content: Quote from: Seekonk on December 10, 2015, 10:07:47 pmI have 1700B . They made great gear.