Resources for troubleshooting non-working circuits?

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jonkull
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Resources for troubleshooting non-working circuits?

Post by jonkull » Wed Oct 28, 2009 1:39 pm

Since 3 out of 5 of my DIY projects ended up in the 'not working bin'...also known as the trash I've decided it's time to learn how to troubleshoot circuits. I'd like to know if anyone can recommend a good book or web based resource that explains how to test/repair non-working circuits. Right now I use the replace each part until it works method which is expensive and time consuming.

Thanks.
If only someone would invent a synth that would allow the end user to determine the functionality. You could pick which functions were important to you in 'modules'. A 'modular', if you will. - Stretta

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haiku-ish
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Post by haiku-ish » Wed Oct 28, 2009 1:54 pm

DEBUGGING - What to do when it doesn't work...

http://www.diystompboxes.com/smfforum/i ... ic=29816.0

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Luka
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Post by Luka » Wed Oct 28, 2009 1:56 pm

just post question here and on electro-music

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sduck
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Post by sduck » Wed Oct 28, 2009 3:11 pm

:agree: And don't be afraid to ask! And try to direct questions to where the designer might be looking. I don't think there's anything on specific debugging for synth diy, short of learning EE from scratch.

I find that just staring at non-cooperating modules for extensive periods of time can work wonders, especially after getting some sleep after the initial comprehension of non-functionality. Eventually you start seeing problem areas.

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consumed
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Post by consumed » Wed Oct 28, 2009 4:01 pm

my very first DIY project was a CGS synthacon filter.
it also did not work off the bat and i looked it over extensively.
it is still in my parts bin but im pretty sure now what is wrong without looking at it
i put the transistors in backwards.

the very first thing you must have is a digital multimeter.
here's what ive learned:

always take your time.
try to assume nothing. if you dont understand a part of the puzzle, spend some time researching it.

if you are unsure or just want to be 100%, always measure your resistors without touching the leads--
dont rely on the color bands because they can be deceiving, and
touching the leads while measuring can give you bad readings.

dont forget to put wire links where necessary on single sided boards (cgs).
check datasheets for transistors/ics/etc for pinout info to be sure a part is aligned correctly
look over your soldering and make sure you have no bridges or have missed anything
look in forums for other builders who have run into the same problem.

take a nice hi-res pic of your project and let some of us look over it too.

so which projects have failed?

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jonkull
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Post by jonkull » Wed Oct 28, 2009 4:12 pm

consumed wrote:so which projects have failed?
Two Midibox SIDs and a VCS. The SIDs are long since gone. I'm trying to figure out the VCS now (that was another post). I have some other things I'd like to build in the future but my failure rate so far is making me reconsider DIY as a hobby mainly because if I build something and it doesn't work...that's kind of where it ends. A non-working 'thing' and time and money wasted. I finally decided to outsource the Klee and my Attenuverting Mixer is on hold until I figure out the VCS.

As far as which ones have worked...a Midibox SID (third one's a charm) and my dual real ring mod (though that one's so simple a monkey could build it).
Last edited by jonkull on Wed Oct 28, 2009 4:14 pm, edited 1 time in total.
If only someone would invent a synth that would allow the end user to determine the functionality. You could pick which functions were important to you in 'modules'. A 'modular', if you will. - Stretta

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RF
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Post by RF » Wed Oct 28, 2009 4:14 pm

I agree with feeling free to use the 'brain trust' here and at Electro-Music - it's probably easier than schlogging through a book...but this one is good.

"Troubleshooting Analog Circuits" Robert Pease


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Post by fonik » Wed Oct 28, 2009 5:53 pm

http://www.musicfromouterspace.com/anal ... shoot.html

in my personal experience the most frequent mistake is wrong wiring, followed by wrong values, followed by cold solder joints. once or twice i have had a damaged part. once i even forgot to insert the ICs...

so after thinking about the problem and possible causes, i always greenline the schematic first, starting at the suspicious section: i take a green pencil, the schematic and my DDM. i check for continuity and values and paint the verified parts on the schematic with the green pencil. i bet this would work with any other colour...
if appropriate i use my scope for checking signal flow with powered module.

when i am done and clueless, i ask in the forum(s).
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Post by frijitz » Wed Oct 28, 2009 7:10 pm

Begin by checking the PS voltages, and that they are reaching each IC.

Then find the individual subcircuits for the various inputs and controls. Put a signal into each input and try to follow it through the circuit. Eventually you will find a point where a subcircuit has an input but no signal output. Your problem is right around there somewhere. It's not always this simple, but if you are willing to poke around and follow the signal flow you'll have a decent chance of finding something wrong.

:grin:

Ian

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Post by neandrewthal » Wed Oct 28, 2009 11:48 pm

fonik wrote:http://www.musicfromouterspace.com/anal ... shoot.html

in my personal experience the most frequent mistake is wrong wiring, followed by wrong values, followed by cold solder joints.
My biggest problem is joints I've completely forgot to solder followed by transistors. I H :flamey: TE transistors!

My Steiner filter didn't work either, so just for the hell of it I tried reversing the transistors in case I got stupid backwards ones again. Nope, so I put new ones in the correct way. Worked.

I had 2 lfos not working in my doomsday machine so I decided to redo the transitors. I accidentally redid one of the lfos that was working too and now it's busted along with the other 2 :mad:

brb, gotta fix my modulo magic :roll:
Initiate the sequence, create catastrophe.

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Luka
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Post by Luka » Thu Oct 29, 2009 2:54 am

my steiner didnt work either
it has been the only module ive given up on

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Tim Stinchcombe
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Post by Tim Stinchcombe » Fri Oct 30, 2009 1:09 pm

RF wrote:...but this one is good.

"Troubleshooting Analog Circuits" Robert Pease
Agreed that is a good book, but in no sense is it aimed at the beginner or novice - useful for the seasoned engineer it may be, but as for 'entry-level', forget it!

Tim

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Post by jonkull » Fri Oct 30, 2009 1:28 pm

I'll have to take a look at some of these suggestions but in the meantime I think I may move the VCS to the scrap heap and move on with my life. I can't for the life of me figure out what's wrong with this thing. I have 12V coming off of ground somewhere in the rise circuit but can't figure out where. Everything looks the way it should.
If only someone would invent a synth that would allow the end user to determine the functionality. You could pick which functions were important to you in 'modules'. A 'modular', if you will. - Stretta

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futuresoundsystems
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Post by futuresoundsystems » Fri Oct 30, 2009 1:32 pm

fonik wrote:once i even forgot to insert the ICs...
The number of times this has happened to me....
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Tim Stinchcombe
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Post by Tim Stinchcombe » Fri Oct 30, 2009 2:10 pm

Just over 5 years ago, whilst making a huge change in career direction, I too was looking for book titles that might help me bolster my then very embryonic troubleshooting skills. I found (and bought) two titles:

Electronic Troubleshooting & Servicing Techniques, Wilson & Risse, Prompt Pub., 1998

The Complete RF Technicians Handbook, Sayre, Prompt, 1998 (as the title says, it clearly has a 'radio frequency' slant, but there is a large chapter on troubleshooting and using test equipment)

Other than a quick skim through each at the time, they have remained largely untouched on my bookshelf (but then I was in an environment whereby work colleagues could offer help and advice).

On searching for 'electronic troubleshooting' at Amazon.com it seems there may be quite a few more titles on this subject available now - reading user reviews may give an indication as to how good any particular title is.

Now, 5 years later, I would say there are 4 key ingredients to successful troubleshooting, in something of increasing difficulty of acquiring each:

1. will-power
2. test equipment
3. experience
4. understanding

The first, 'will-power', it seems you may have crossed - you must really want to get the wretched circuit working no matter what it takes (though I have to say time is an important factor here too - the longer it takes, the more the will-power will wane).

Secondly, some test equipment is a must - a good DVM is essential, and as well as measuring voltage, current, resistance, continuity etc., a diode checking facility is invaluable for testing not only diodes but BJT transistors; add an oscilloscope too and many more avenues for testing and troubleshooting become available - it is just immeasurably easier when you can see that waveform on a scope.

Number 3, experience: the more you do it, the easier it becomes, as you learn what caused a particular problem, you may recall it in the future, and save much precious time (which is pretty much true of any endeavour in life in general I guess).

The fourth is probably the hardest to acquire: an understanding not only of the basics of electronics, but particularly how that applies to the circuit in hand - if you don't know what you are looking for/what to expect, then you will not know if you are looking at it! Unfortunately there is little substitute here except for good old fashioned grafting away at text books/taking a course/looking at loads of schematics trying to fathom out how they work, and following discussions on various problems in this and other similar forums. I will add that it is often possible to troubleshoot a circuit without a detailed knowledge of how it works (technicians do it all the time), but you still need to know what to expect, perhaps by having someone who does know what the circuit does telling you.

Well, that's my philosophy any way!

Tim

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Post by pugix » Sun Nov 08, 2009 9:14 pm

Don't forget patience and curiosity. I've fixed audio and video synthesis circuitry since 1975. So I have plenty of experience. And I have a good DMM and an old 'scope. For dead circuits, after I've triple checked the construction visually, and I know the power supplies are good, I start scoping around. A scope probe can have some unexpected effects, because it physically disturbs a circuit (as can a finger). I fixed a Mankato VCF I bought as non-working just by poking around. It started oscillating whenever a bit of pressure was placed on a capacitor that was intermittently open. That was the whole problem. This is typical: there is one problem and you only need to find it.

Here's a story. The hardest time I had making a module work was my CGS burst generators. I had built two and neither worked. Scoping around, I saw pulses seemingly coming out of IC input pins! It was baffling. Ken Stone gave me lots of pointers. In the end it turned out that the CMOS ICs were malfunctioning. Replacing them with Texas Instrument brand fixed it. Now I always use T.I. CMOS whenever possible.

Richard

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Post by tony d » Sun Jan 27, 2013 1:33 pm

I just wanted to bump this thread because there's a ton of great info/links in here.I've had a lot of builds recently that haven't worked out of the gate and each one was a unique problem but i was able to get every one working with a little patience and persistence, and i learned a ton in the process.

Maybe it's worth making a sticky for a "troubleshooting checklist" ?

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Post by pulsewidthmod » Sat Feb 02, 2013 10:58 am

tony d wrote:I just wanted to bump this thread because there's a ton of great info/links in here.I've had a lot of builds recently that haven't worked out of the gate and each one was a unique problem but i was able to get every one working with a little patience and persistence, and i learned a ton in the process.

Maybe it's worth making a sticky for a "troubleshooting checklist" ?
i agree and thank you!

here's where i am stuck ... i have a multimeter but i don't know how to use it with testing my fx pedal .... i'll go on to google and youtube and do a search

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Post by decaying.sine » Sat Feb 02, 2013 11:06 am

pulsewidthmod wrote:
tony d wrote:I just wanted to bump this thread because there's a ton of great info/links in here.I've had a lot of builds recently that haven't worked out of the gate and each one was a unique problem but i was able to get every one working with a little patience and persistence, and i learned a ton in the process.

Maybe it's worth making a sticky for a "troubleshooting checklist" ?
i agree and thank you!

here's where i am stuck ... i have a multimeter but i don't know how to use it with testing my fx pedal .... i'll go on to google and youtube and do a search
Here's a couple resources...
http://www.sparkfun.com/tutorials/202

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Post by home_listening » Sat Feb 02, 2013 9:40 pm

In my experience there is nothing better than going to bed, sleeping for a long time and reapproaching the problem after a good breakfast, long walk and a nice coffee.

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Ykratka
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Post by Ykratka » Sat Dec 27, 2014 4:06 pm

Hello guys!

I've had to register another time after i forgot my account info after a long absence, and i remember having seen an 'introduce yourself' topic somwhere on the forum but couldn't find it this time. So here i am, and with a problem.
(If there is a specific thread for newbies please direct me there and/or move this message there as well.)

With that said. I have built some basic oscillators and droning synths several years back so my experience is slightly above zero. Recently i have been asked by a friend to construct a simple 4-6 oscillator circuit for droning purposes. I had one of my ancient unfinished stripboard projects lying around so i went to check it to his place and surprisingly it worked. It's the most basic 40106 oscillator (theres place for more of them off course). at home i tried to transfer it to protoboard and it worked no more. All the response i got from it were quiet clicks as i connected the speaker to the circuit- nothing more. When i measured the voltage between ground and the supposed output it showed 4.5 volts- exactly half the supply voltage. I tried making it on breadboard- same result. Tried several different IC's- same result.
Now I'm all out of guesses. There's literally nothing to break in the circuit- its that basic, and still it refuses to do anything beyong giving me 4.5 volts on output.

Thanks for any help/suggestions in advance. One good advice I already have obtained is to go have a break and thats what I am going to do lest my brain boils.

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Post by daverj » Sat Dec 27, 2014 4:20 pm

Do you have a scope or just a voltmeter? The problem with a meter is that it doesn't distinguish between a pure DC signal and an average DC signal. So a signal that is oscillating between zero and 9 volts will measure 4.5 volts on a meter (unless it oscillates really slowly).

One simple home-made piece of test equipment you can make easily is an LED with a series resistor to limit the current) and a pair of alligator clips on wires connected to it.

You can clip this at a point where you think there is an oscillation. If it's a slow oscillation the LED will blink. If it's a fast oscillation then it may blink so fast it looks solid. But here's the cool trick: Wiggle the LED as fast as you can and you might see that it is in fact pulsing on and off.

It's even better with a two-lead red/green LED. Then it changes color as it goes positive negative and you don't have to swap the leads if you see nothing, to be sure it's connected right.

Of course this trick doesn't work if the signal is so small that it doesn't reach the LED on voltage.

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Ykratka
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Post by Ykratka » Sat Dec 27, 2014 4:39 pm

Yes its just a voltmeter. I guess that could be the reason why it measures 4.5v.
But still- those average 4.5v should at least have some effect on the speaker not just clicks? I tried an 8Ohm speaker and another one from an old telephone with no success.

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Ykratka
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Post by Ykratka » Sat Dec 27, 2014 4:48 pm

Just tried placing a LED from ground to output pin and it just stays lit up. Added a bigger cap (220uF)- with 1M pot it should tick kinda slowly but the LED just shines permanently.

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Ykratka
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Post by Ykratka » Sat Dec 27, 2014 5:12 pm

Update: I accidentally placed a speaker across pins 1 & 2 of the IC and there was a high pitched bleep which wasnt affected by turning the pot.
Could it be that i fried 3 IC's in a row and need another one to get it to work?

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