Troubleshooting with an Oscilloscope

[killian6pk]

Can anyone point me to a really good book on how to troubleshoot circuits with an Oscilloscope. I have read two so far (How to Use Oscilloscopes and Other Test Equipment by R.A. Penfold) and another (Troubleshooting with Your Triggered Sweep Oscilloscope by Robert Goodman). Both are good books, but spend most of the book talking about the controls and wave forms etc. without actually getting to the nuts and bolts of using the scope for finding faults with circuits. I guess I need a Dummies book. I am trying to repair computer LCD monitors and need to be able to find faulty components within the circuit boards. Any help you could give me would be appreciated.

 

[Brevor]

I dont know of any o-scope books but Im drinking a Killians right now.

 

[mdanh2002]

You don't need an oscilloscope to identify and fix most of the repairable problems in CRT/LCD monitors. A multimeter, a repair guide and some expertise, either from you or from somebody willing to help you, are far more important.

 

[killian6pk]

If you like Killians

Try a Smithwick's. It is made by Guinness, but not as dark. It is an Ale that is darker than most Ales you see similar in color to Bass. You can find it at most large discount beer stores and Kroger carries it in our area at least. It is all I drank while we toured Ireland. There is another beer that I have run into that I think is great called Bodington's Pub Ale. Made in England it is a little harder to find than Smithwick's. Drink one for me.

 

[crutschow]

An oscilloscope can be used to easily trace signals in a circuit to find where the signal is abnormal or absent. The bigger problem is not tracing the signals but finding a schematic of the failed circuit to know where the signals are.

 

[killivolt]

An oscilloscope can be used to easily trace signals in a circuit to find where the signal is abnormal or absent. The bigger problem is not tracing the signals but finding a schematic of the failed circuit to know where the signals are.

I agree though, I'm no pro at an oscilloscope. I remember that their is a lot of references to the type of signal in the schematics. Even better if the manufacture will put in field bulletins to aid you in your search for the problem. Many times they have a field corrections narrow the problems directly to the source.

 

[colin55]

The biggest problem with an oscilloscope is this:
You will probe a particular point in a circuit and view a signal. The trace may have a number of glitches and spikes and irregularities and you will not know which parts of the signal are creating the problem.
Many times, a CRO image will be more frustrating than it is worth.
A previous poster has a very good suggestion. A simple multimeter and logic probe will locate a lot of faults in a digital system and by simply adding extra filtering (electrolytics and 100n capacitors) you will be able to solve most problems.
You have to be an absolute expert to INTERPRET a CRO trace and since very few circuits include CRO readings, you have very little chance of it “homing in” on a problem.
If you want assistance in this area, the only answer is to set-up a faulty circuit, post an image of the trace at various locations, along with the circuit and the experts in the forum will guide you.
An equivalent book would be 1,000 pages thick.

 

[Dean Huster]

Troubleshooting is mostly handled through the understanding of block diagrams, schematic diagrams, signal flow, etc. learned in troubleshooting texts and by experience. Scope operation is a secondary factor. Knowing how to use all of his tools to the nth degree does not make a good automobile mechanic.

 

[killian6pk]

When you talk about signal tracing are you talking about tracing with the AC power hooked up or signals from a signal generator of some type. Is it possible to use a low power DC power supply to furnish a current through the circuit and trace with that?

 

[colin55]

You can trace signals on a 3v transistor radio.

 

[Louis Estrada]

Can anyone point me to a really good book on how to troubleshoot circuits with an Oscilloscope. I have read two so far (How to Use Oscilloscopes and Other Test Equipment by R.A. Penfold) and another (Troubleshooting with Your Triggered Sweep Oscilloscope by Robert Goodman). Both are good books, but spend most of the book talking about the controls and wave forms etc. without actually getting to the nuts and bolts of using the scope for finding faults with circuits. I guess I need a Dummies book. I am trying to repair computer LCD monitors and need to be able to find faulty components within the circuit boards. Any help you could give me would be appreciated.

For some time, I had also been looking for "hands on" information and found this discussion but no definitive answer. Further digging led me to three videos in YouTube which I believe will be helpful to others and is a good beginning point. Here they are.
video 1, What is an oscilloscope:

video 2, Basic usage:

video 3, Advanced functions:

Better late than never. Cheers!

 

[crutschow]

When you talk about signal tracing are you talking about tracing with the AC power hooked up or signals from a signal generator of some type. Is it possible to use a low power DC power supply to furnish a current through the circuit and trace with that?

We are talking about the signals when the circuit is powered normally, whatever power source that is.

If you use a DC power source then how much you can trace depends upon whether the circuit is designed to operate with a DC signal. And if you use DC you don't need an oscilloscope, just a multimeter.

 

[tvtech]

My two cents:

As a CRT tech I probably use a Scope maybe once in every 100 or so sets. Only use it when I am stuck and need to check pulses on the Line or Frame stage..

Other than that no. A good Analogue Meter and common sense is enough. And waaay quicker.

Regards,
tvtech

 

[Nigel Goodwin]

My two cents:

As a CRT tech I probably use a Scope maybe once in every 100 or so sets. Only use it when I am stuck and need to check pulses on the Line or Frame stage..

Other than that no. A good Analogue Meter and common sense is enough. And waaay quicker.

You're probably wasting a lot of time then

Even back on CRT sets a scope is a lot more important than only 1 in 100 sets

PSU faults, line faults, frame faults, colour faults, luma faults - lot's of examples where getting the scope out sooner rather than later can save a great deal of time.

 

[tvtech]

You're probably wasting a lot of time then

Even back on CRT sets a scope is a lot more important than only 1 in 100 sets

PSU faults, line faults, frame faults, colour faults, luma faults - lot's of examples where getting the scope out sooner rather than later can save a great deal of time.

LOL Nigel. You have lost it

Remember, all Ching stuff here now. Mostly no need for anything other than a Multimeter on almost every fault.
These sets have Jungle/Micro combinations in one Chip. They do fail but rarely so. Hence the 100 set chirp...

It's mostly about SMPS and LOPTX failures. SMPS's all built basically the same...all fail the same way.
And then LOPTX's.....a real PITA. LOPTX gets a crack, arcs over to SMPS heatsink...bang....PSU stuffed/blown up.

Yes, some of the sets require a scope to fix, for example when Horizontal drive is missing from the Jungle/Micro....but generally few and far between.

Heck I miss the days where TV repairs were a real challenge. And a Scope was a necessary tool. And nobody fiddled inside the chassis....because it burnt and bit you if you did not know what you were doing. No SMPS or isolation from Mains....

Raw power that punished fools. Even cockroaches were afraid to live in the older sets....

Regards,
tvtech

 

[playsafe]

Can anyone point me to a really good book on how to troubleshoot circuits with an Oscilloscope. I have read two so far (How to Use Oscilloscopes and Other Test Equipment by R.A. Penfold) and another (Troubleshooting with Your Triggered Sweep Oscilloscope by Robert Goodman). Both are good books, but spend most of the book talking about the controls and wave forms etc. without actually getting to the nuts and bolts of using the scope for finding faults with circuits. I guess I need a Dummies book. I am trying to repair computer LCD monitors and need to be able to find faulty components within the circuit boards. Any help you could give me would be appreciated.

Hi, for a beginner. using oscilloscope for repair and using V-I curve look cool but usually we using it as one of the last resort or on very high complex circuit board. To repair LCD monitor, 1st locate the power supply, video and inverter for backlight board. 1st check the physical faulty you can see. it might be blown or open capacitor and etc. if no physical sign of damage then check the power supply system to the board. check the output. minimize the possiblity as small as you can.

regards,
IeSS, playsafe

 

[crutschow]

And another newbie practicing the art of necromancy.

 

[JimB]

And another newbie practicing the art of necromancy.

A newbie who joined ETO nearly three years ago!
Very strange.

JimB

 

[Tony Stewart]

For learning, reverse engineering a commercial or consumer product with a service manual or schematic is better training than DIY designers who know enough to get frustrated.

Learn how to;
- get textbook waveforms above 30MHz is relevant using very short leads just the internal tip & ring beteen test pins added
- get stable triggering on repeating sub harmonics or modulation rates or look at clock/data skew, timing margin
- capture glitches reliably
- capture a data burst or just the same video row every time
- use an FM gen to make sync'd frequency response curves
- analyze resonance on spark gaps, transmission line faults or locate EMI hot spots in new circuit designs.


To know how to use a scope well is to love it.

It is essential to becoming a great design verification and/ or Test Engineer.

Some of these and more;
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http://learn.sparkfun.com/tutorials/how-to-use-an-oscilloscope

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But I agree for repair, shortcuts just need understanding of faults due micro/solder fractures, dust leakage, CFL wearout , dead pixel rejuvenation tester and a meter with good service guide.

Feel free to ask specific how-to?

 

[playsafe]

A newbie who joined ETO nearly three years ago!
Very strange.

JimB

Haha,
After running my own company for few years only now i have free time to write or reply a post. Yeah I'm still a newbie though.