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Tracing the signal without a scope

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I've been working on a project at school where I had access to a big variety of test equipment. I no longer have access to anything but a basic meter.

I have a circuit that amplifies/filters a signal to light LED's. I took it out of the box to draw a schematic. When I tried to use it again, absolutely nothing happens. At school I would just power it and use the scope to see where the problem is.

I would see if the signal amplified on the output of the first op amp, if yes, see if it is on the output of the filter, etc.

How would I go about diagnosing the problem with out a scope?
 
Not too many good alternatives:

  • Use a simulator (like LTspice) to run the circuit on your computer and diagnose it;
  • Use an audio amplifier to extract signal from various points in the project

Without a 'scope, you're pretty much shooting in the dark ...
 
What's your budget?
 
Hmmm, not sure really.

$100? I'm not quite ready to spend a lot of money for this hobby yet.

But if there is some day and night difference between a $100 and a $250 scope, I might get the $250 one. The ~$1000 scopes are absolutely out of the question for the moment.
 
There is a night and day difference between a new 100 dollar scope and a used 250 scope. Do your research on ebay and in the forums here. In your price range new is a crime against intelligence, so is a rushed purchase. Take your time and give yourself two weeks to research it when you can. You'll pay dollars for every penny of research you fail to do.
 
Ok thanks.

But in the mean time, is there anyway to figure out the problem in this circuit? It would be extremely inconvenient to not have this circuit not working for a month.
 
The link you gave is the PDS5022S 25Mhz, not 50MHz Owon scope. Sampling record length is only 5k, too low for any serious digital debugging.

Try to get the Rigol DS1052E 50Mhz - it's better in my opinion.
 
What is the expected voltage range and output impedance of the point you want to test?
 
If it worked at one time it may well be a bad connection. You might get an idea where the problem is by measuring the DC output at each stage to see if one of the op amps is at the rail.
 
You can build yourself a simple Logic Probe, Signal Injector and Bench Amplifier. I have only used these 3 things to solve almost all problems as I know very few hobbyists have a CRO on-hand and to mention a CRO simply "loses them."
 
There are extremely low-bandwidth scope kits out there:

**broken link removed** (sub $50.00)

Then there's the DSO Nano:

**broken link removed** (sub-$100.00)

While I wouldn't consider either of these to be "be-all-end-all" solutions, and would generally advise you to save your money for a proper scope (if you can find used, only buy if you can test it first-hand); but if you need something "now", those are options, and are fairly good for audio-signal tracing (and a lot of other hobby stuff, too).

If you can't wait that long, though - there are plenty of PC-based projects out there that use the soundcard on a PC for audio-level stuff; I would reccommend that if you go this route, though, that you use/build a separate "throwaway" PC with a separate soundcard, so if you blow anything, you've only wasted an old PC (a dumpster pentium PC is perfect) or cheapo soundcard, and not your main workstation. It might be enough to find your problem...

Good luck.

:)
 
Hi OP where do you live?.

Only reason I ask is if it is close to me your more than welcome to use my one I got only a few days ago.
 
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