Circuit works on breadboard but not PCB

Thread Starter

juve786

Joined Jul 13, 2010
27
Hi, I made a microphone circuit using the schematic:Electronics Projects For Dummies Parabolic Microphone and was successful and fun on a breadboard. I then wanted to make this smaller - i.e. on a PCB but i had no luck. I had my college etch a board for me which i checked was ok, but he circuit didnt work, and then I recreated the design on a matrixboard joined with copper tracks.

What could be the issue? I tooked the components apart and recreated them on a breadboard and it works fine again :confused::(

Also, regarding the copper track i use (it is copper tape) - how do I join the tracks? the adhesive is acrlyic and non conudcive and i have to join them by painting some leitsilber l100 over it and its very annoying:mad:

thanks!
 

SgtWookie

Joined Jul 17, 2007
22,230
You used the same components on the breadboard that were removed from the PCB?
In that case, the parts are good, but either the soldering was not good or the PCB design was not correct.

Without seeing the PCB, it will be impossible to say what the actual problem was.
 

mcgyvr

Joined Oct 15, 2009
5,394
I've soldered to copper tape many times..

As to why it doesn't work on a PCB and does on a breadboard..Are you sure the PCB has the correct traces/connections,etc... What doesn't work about it?
 

Thread Starter

juve786

Joined Jul 13, 2010
27
You used the same components on the breadboard that were removed from the PCB?
In that case, the parts are good, but either the soldering was not good or the PCB design was not correct.

Without seeing the PCB, it will be impossible to say what the actual problem was.
Yes i used the same components on every attempt - i even replaced the lm386n-1 to make sure it wasnt that - same problem.

I checked the connections with a continuity tester on my multimeter and it all seemed to be fine.

I will try putting up both my pcb track designs (made by circuit wizard)

*** edit ***
heres my PCB track
 
Last edited:

windoze killa

Joined Feb 23, 2006
605
Any chance of posting the picture of the PCB directly to the forum. I can not access external picture sites from here at work.

One thought that crossed my mind that occurs a lot. Did you remember the power pins on the ICs. Some schematic programs hide these and you can forget to connect them.
 

Thread Starter

juve786

Joined Jul 13, 2010
27
Any chance of posting the picture of the PCB directly to the forum. I can not access external picture sites from here at work.

One thought that crossed my mind that occurs a lot. Did you remember the power pins on the ICs. Some schematic programs hide these and you can forget to connect them.


Yes all the pins are connected as they should be:)
 

windoze killa

Joined Feb 23, 2006
605
There is one fault I can see but not sure if it will cause a problem. C2 is reversed on the PCB. You have the + side going to pin 8 but on the schematic the + side goes to pin 1.
 

Thread Starter

juve786

Joined Jul 13, 2010
27
OH wow...
even though thats true im pretty sure i paced the compoents properly but who am i to say that :p
I thought the circuit was wrong so i pulled all the copper tapes off the board so i could reuse it for something else, but ill do it again and carfully place the components this time and let you know how it goes.
Do the tracks seem OK though?
thanks a lot btw
 

eblc1388

Joined Nov 28, 2008
1,542
A very simple mistake in PCB making is to make the PCB with tracks as shown. Those tracks above are shown to be looking through the PCB via the component side and will not be visible physically.

With the copper tracks of the final PCB facing you, your final PCB should show tracks that are mirror image of that shown above.

If the copper tracks look exactly like above, you are doomed.
 

Thread Starter

juve786

Joined Jul 13, 2010
27
when i printed the track out i rememebered to mirror it. i can hold both components and track printouts back to back and they fit on each other as they should. thanks though. let me get out of bed and carry on recreating the track :p
 

Thread Starter

juve786

Joined Jul 13, 2010
27
SUCCESS!
I guess i was stupid enough to miss out that backwards capacitor after all. At least i know i cant trust circuit wizard all too much :p

Thank you all SO SO much for all the time and help youve given.
Wish you all the best!
:D:D:D:D
 

Thread Starter

juve786

Joined Jul 13, 2010
27
im a bit new to all of this, which is why i only make projects that i find rather than design my own (im only 18 and hope to start an electronics eng. degree this coming academic year)
but despite that i clearly love my subject and enjoy learning ahead.
what difference does a polarised cap make? and how is their use over a non-polarised decided?
i just know basics how they store charge, time constant, only ac currents can pass etc etc.. but id go to say i no practically nothing atm :p
 

tom66

Joined May 9, 2009
2,595
Polarity of a capacitor generally only affects its lifespan. Electrolytic capacitors are designed so that they only work one way round... and they can catastrophically fail if they are reversed. That means they can explode, leak, and sometimes catch fire especially for tantalum capacitors. I don't quite remember the reason, but it's more expensive to make non-polar electrolytics, and it makes them bigger in size. In most cases polarity is not an issue, because electrolytics are often used to filter DC voltages and not much else. They have some applications in timing circuits and in a.c. coupling applications too, but their imperfect behaviour (e.g. dielectric absorption, polarity) makes them perform poorly.

Have a look here:
http://www.youtube.com/watch?v=akCI_Hm9iE0
 

Thread Starter

juve786

Joined Jul 13, 2010
27
oh ok, that helped a bit. So i guess i was lucky my circuit only needs 6V and i didnt leave it on too long when i most likely had that cap backwards :p
thanks a lot guys!
now to remove the hissing in the background! any suggestions? or is that inevitable with audio circuits as simple as this?
 

dsp_redux

Joined Apr 11, 2009
182
A ground plane could help. Also, don't use polarized caps on your signal. Film caps is what you need. Polarized caps are used mainly for decoupling and filtering ripples on DC power supplies.
 
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