Knight of Tone - half working?

[rpark71]

Hi,

Just finished (PCB Mania) Knight of Tone pedal and as usual with my builds, there's a problem! Only the right side of the pedal circuit works as designed. When I then press the left foot switch , the LED comes on the pedal no longer works (both LEDs still lit). Turning volume knob on left side does make a crackle/hiss noise, and there's a audible click/pop when you switch the mini toggle, but still no sound. If I turn both footswitches off, guitar signal goes to amp. I did test outside of the enclosure - it was a few weeks ago and from memory I'm sure all worked ok. Does this sound like a short-circuit somewhere? Another facebook forum suggested the footswtich lugs need filling completely, so can try that, but thought I'd query here, as the expert folk here solved my last two pedal problems! Right side sounds good as least! Any help or direction welcome.

thanks, Rich

[Boba7]

Yeah, I'd definitely start by checking the soldering, it doesn't look quite alright to my eyes. Some lugs on the footswitch might not make contact.

[jimilee]

While it's not necessary to fill in the whole eye, it's hard to tell if there's any solder at all. Without seeing the back of the board, it's hard to tell anything about the circuit. Are you getting voltage readings and you you have an audio probe to see if you're getting audio across the switch?


Sent from my iPhone using Tapatalk

[rpark71]

Had to go find out how to check the voltages and understand that its usually just the IC's and transistors that you measure? So the three IC's read:

IC1 (side not working)
1. 16.62v, 2. 16.53v, 3. 15.44v, 4. 15.92v, 5. 15.29v, 6. 15.36v, 7. 16.55v, 8. 17.19v

IC2
1. 15.42v, 2. 15.44v, 3. 14.06v, 4. 0v, 5. 15.29v, 6. 15.31v, 7. 15.26v, 8. 17.19v

IC3
1. 9.26v, 2. 5.91v, 3. 0v 4. -2.97v, 5. -3.04v, 6. 4.44v, 7. 5.74v, 8. 9.26v

I'm guessing the 0v and negative V readings are part of the issue - but not sure if that's normal as IC3 is the voltage doubler chip in the circuit. Nice to learn about voltage readings! I'm none the wiser, but might help you identify something.

thanks, Rich

[Bio77]

You have all your ground leads connected to the DC jack, which is plastic.  You should connect the PCB ground and the ground pin of the DC Jack to ground lug on the input jack.  You should also sand the paint on the inside of the enclosure by the input jack, so, it makes good contact.

[Boba7]

Had to go find out how to check the voltages and understand that its usually just the IC's and transistors that you measure? So the three IC's read:

IC1 (side not working)
1. 16.62v, 2. 16.53v, 3. 15.44v, 4. 15.92v, 5. 15.29v, 6. 15.36v, 7. 16.55v, 8. 17.19v

IC2
1. 15.42v, 2. 15.44v, 3. 14.06v, 4. 0v, 5. 15.29v, 6. 15.31v, 7. 15.26v, 8. 17.19v

IC3
1. 9.26v, 2. 5.91v, 3. 0v 4. -2.97v, 5. -3.04v, 6. 4.44v, 7. 5.74v, 8. 9.26v

I'm guessing the 0v and negative V readings are part of the issue - but not sure if that's normal as IC3 is the voltage doubler chip in the circuit. Nice to learn about voltage readings! I'm none the wiser, but might help you identify something.

thanks, Rich

Nope. You want to have a 0v reading at pin4 of both opamps (IC1 & IC2).
The opamp on the non functionning side isn't grounded at pin4. You have a ground issue, maybe a short between pin 4 and another pin or component.
Check your soldering, reflow gently everything, and inspect carefully pin4 of IC1.

[rpark71]

Ah, ok - I think on every build so far I have a ground issue! Thanks for the advice on the DC jack grounding and the IC voltages. I'll take a look at the ground wires first and then at the IC1. Really helpful - thanks! I may be back with more queries!

[jimilee]

On the gut shot, on the left presence pot, are all 6 pins soldered?



Sent from my iPhone using Tapatalk

[rpark71]

Yes, maybe can't see as in shadow of the capacitor.

I actually tried just removing the IC1 chip to check pin 4 not bent or something and replaced it and then tried plugging in again and it worked both sides until I flicked the left toggle switch to test that. Could it be the toggle - as the solder there isn't filling the holes like the  footswitches.

As an aside, I thought I'd read somewhere that not flooding holes on switches was best as it can lead to a short in the switch, which is why I tried to add solder to just one side. Maybe I misunderstood?

thanks, Rich

[jimilee]

Yes, maybe can't see as in shadow of the capacitor.

I actually tried just removing the IC1 chip to check pin 4 not bent or something and replaced it and then tried plugging in again and it worked both sides until I flicked the left toggle switch to test that. Could it be the toggle - as the solder there isn't filling the holes like the  footswitches.

As an aside, I thought I'd read somewhere that not flooding holes on switches was best as it can lead to a short in the switch, which is why I tried to add solder to just one side. Maybe I misunderstood?

thanks, Rich

Not flooding the holes is no big deal as long as there's a strong connection.


Sent from my iPhone using Tapatalk

[Govmnt_Lacky]

That brown electro cap sitting above the toggle switches in your pic.

That scares me a little 

[Boba7]

That brown electro cap sitting above the toggle switches in your pic.

That scares me a little 

Oh yeah definitely!

[rpark71]

Yeah, I did have to bend that out the way but did double check it wasn't touching anything or that the leads were touching. I have since raised it a bit too. Will look at changing the green ground wire from dc jack to ground lug of input jack as suggested. It is wired as per diagram from PCB Mania but willing to try it! Have removed from case now too to check other side of pcb.

Thanks, Rich

[rpark71]

Hi - Just an update on this as had some time yesterday. Removed from enclosure, sanded down inside input jack to remove the paint coating a bit, moved ground wire from pcb to the input jack ground lug and resoldered pin 4 of the IC1 socket - even remembered to remove the IC first!  Then I took new voltage readings, which for interest are as below:

IC1: 1. 8.62v, 2. 8.62v, 3. 7.83v, 4. 0v, 5. 8.45v, 6. 8.48v, 7. 8.42v, 8. 16.94v
IC2: 2. 8.62v, 2. 8.62v, 3. 7.83v, 4. 0v, 5. 8.45v, 6. 8.48v, 7. 8.42v, 8. 16.94v
IC3: 1. 9.23v, 2. 5.84v, 3. 0v, 4. -2.96v, 5. -3.01v, 6. 4.42v, 7. 5.72v, 8. 9.23v

Tested and now both sides working and sounding great! Thanks so much for advice and ideas. Better learning experience when it goes wrong I guess!

Cheers, Rich

[Boba7]

Great, I'm glad to read that!
Debugging is always a good teacher