First build- signal cuts out after 2 seconds.

Frequent questions about dead or faulty pedals. Whether you repair, mod or build pedals, debugging is important. Threads about general debugging problems irrespective of the circuit involved...
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CanuckAbroad86
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Post by CanuckAbroad86 »

Hello all,
This is my first build and am relatively new to the game....
Basically when testing my PCB with pots & jacks plugged into an amp via 9V, I get a nice signal for about 2 seconds then it cuts out. Am I overloading the circuit? I've searched around for this issue but haven't found much (or maybe my vocabulary just sucks).

A dropbox link to a video of the issue and whats happening:
https://dl.dropbox.com/u/4506024/Stompbox%20Issue.MOV

Here's the schematic & layout:
http://pedalparts.co.uk/wp-content/uplo ... reamer.pdf

Things I've tried:
Double checking diode/capacitor polarity
Checking resister values
Re-soldering "sketchy" solder joints
Scratching between solder joints/ checking for bridges
Checked Voltage of several components

I'm hoping there's a simple solution to this for people who actually know what they're doing. But hopefully I'll learn from this and continue this hobby for years to come!

Thanks!

microsynth

Post by microsynth »

Can you post pictures of both sides of your PCB? It's generally much more difficult to diagnose a circuit's problem without being able to look at the circuit itself.

UZILSD
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Post by UZILSD »

Check Vref, first off. It must be stable somewhere at 4.5V. Check if it is connected to all the points it should, pay attention not to confuse Vref with ground. Then check if the decoupling capacitors (C1, C2, C3, C8, C10, C11) are in place and not bridged. The problem looks to me like the biasing of some stage is getting fucked up, or a problem in the voltage divider that generates Vref

CanuckAbroad86
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Post by CanuckAbroad86 »

Thanks for you responses guys,
Uzilsd, I've checked the voltages at each point +VR is on the schematic. Vref seems to be ok (5v on my shitty meter) in the input and output buffer stages and also the power section.

The 4 other points throughout the schematic (connected to R5,R6,R16 & Level) all give me 9V. From what I understand this could narrow things down? Upon inspection, the Capacitors look OK.

Here is the top and bottom of the board. (I totally burnt the ground connection after multiple soldering sessions so I attached it to the bottom). Gonna have to invest in some proper tools I think.....what do you think? salvageable?

https://dl.dropbox.com/u/4506024/IMG_0199.JPG

https://dl.dropbox.com/u/4506024/IMG_0200.JPG

Thanks!

microsynth

Post by microsynth »

CanuckAbroad86 wrote:The 4 other points throughout the schematic (connected to R5,R6,R16 & Level) all give me 9V.
Well there's your problem. Those points are supposed to be connected to VR, not power - they should be reading 4.5V, not 9V.

microsynth

Post by microsynth »

So, first thing I would do when debugging this is to check every point where 9V connects to the circuit (transistor collectors, pin 8 of the op amp, d3/c12/r9/rled) and make sure you don't have any stray solder jumping to adjacent pins.

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DrNomis
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Post by DrNomis »

Highly unlikely, but it's possible that R9 might be short-circuited somehow, or you might have put the wrong value resistor in by mistake, or R10 might have dry solder joints on it...... :hmmm:
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CanuckAbroad86
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Post by CanuckAbroad86 »

Thanks for your help everyone! Problem solved. Basically checked R9 & R10 and re-soldered those. Also went around the whole circuit sucking up any excess solder from pins/re-soldering and now I've got the signal! Now to make the box look good......shit.

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Lucifer
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Post by Lucifer »

CanuckAbroad86 wrote:Now to make the box look good......shit.
Most people can make their boxes look "good" - or make them look "shit" - but if you can make yours look "good shit", that'll be really original. Go for it ! :horsey:
”Sex is great - but you can’t beat the real thing !” - The Wanker’s Handbook

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