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debugging a small amp

Started by kin0, May 11, 2011, 11:09:07 AM

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kin0

I checked all the things that are close to the ground of the pcb and none of them is connected to it accidently. Also I checked all the points and none of the points get electricty (except the ones that need).

What else can I check? (I really have no idea so ANY cluse would be welcomed)

kin0


joecool85

Sounds like your resistor pair aren't made up of the proper resistors (R14/R15).  Double check their values.  Maybe even replace them with known correct resistors just to get that out of the equation.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

phatt

Hi Kin0,
         Sorry to hear you are still struggling with this. :'(
At this point you really need to take close up pictures of both sides of the board as that will help a lot.

Simple truth is that (Even with pics) it is sometimes impossible to trouble shoot circuits over the net like this.
Cheers, Phil.

kin0

here are 2 pics but the soldering looks much more dirty then in reality-maybe the flash just shows staff that I can't see regularly or just gives bad light.

phatt

Hi Kin0,
Good pics. :tu:
From what I can see You've connected pin 4 (which is circuit com) to the bias rail via a bridging wire. This effectively shorts out the bias voltage to ground.  So hence it won't work.

Try removing that wire.
The Com track is right beside the bias track as it passes under the chip, easy mistake to make.

I realize that etching your own boards is not easy which is why I tend to avoid it where possible.

For my home builds I rework the pcbs and stretch out the tracks a bit.

These kind of pcbs are really only useable IF you have the right equipment to print, etch and drill the boards.

I hand drew a complex pcb once,,,which did work but never again. xP

Hope it works now.
Cheers, Phil.

kin0

It is my first pcb so i f*cked up some things but I the next one should be better (btw in this one the tracks were to thin for home etching). I'll try to do the thing you said today and post what happens.

kin0

Oh, I tried to find now the wire you talked about but I have a hard time. Can you circle where it is in the picture?

J M Fahey

Hi Kin.
*IF* ou have the ready to transfer PCB design, the pure and clean bottom side, (you posted a "transparent" view from the component side, if I'm not mistaken), I'll make one showing the step by step iron on process, plus etching, drilling and fluxing; I think it might be useful.

kin0

of course I have it. But still can phatt point me to the wire he talked about?

phatt

There is only *One bridging wire* you added that passes under the opamp.
It looks as if it shorts the bias to ground. remove it and see if it fires up.

You have 3 tracks under that chip, 9VDC, Bias and Ground.
Phil.

kin0

Oh, this one. I'll take it out.

joecool85

Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

kin0

Oh finally the R10/14/15 node is 4.6v!!
Now i need start putting things back in place without lowering the voltage. How this can be done (especially with the cap).

kin0

I inserted the C12 and connected it to where it needs to be connected and it's still was 4.6V, how ever then trying to connect the R14/15 node to R11/4/5 node it went down to 1.2V. I think the problem is in this node so I'll take out the wires which I used to recreate the track and try to find another way to recreate the tracks.