SOLVED Mojito...no overdrive

ProfMagpie

New member
This is my second build of this pedal. Wanted a larger enclosure so my size 12s could work one or the other stomp switch. Anywho, the gain pot is not working. Dialing it up and down does nothing but increase volume. When the boost is engaged, I get OD, but not without the boost engaged. Checked voltages against my working pedal. Checked the pots and resistance is what it should be. I'm stumped. Attached are a couple of gut shots. Any advice is appreciated. Thanks!

- Chris
 

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BuddytheReow

Breadboard Baker
Trace the circuit with an audio probe to find your dead spot. This thread will also help you troubleshoot before others put in their 2 cents.

 

Raspymcnasty

Active member
Your soldering job looks good overall but
I see a flux blob or a bridge at the diodes on the right.

I’m going to guess your backside is clean and there are no obvious bridges or cold joints.

Test out the leds with your multimeter and test if the led lights are properly anode/cathode.

If that is good check your ic voltages.

If that looks ok then use a test probe (look up how to make it, it’s really easy) look at the schematic and see where your signal goes.. if you don’t know how to look up a schematic legend, just check continuity for ground, secondly i follow the signal path.

Fyi i am not qualified to answer this but I’m a research freak when it comes to hobbies (motorcycles, drones, p2p keyboards) and this is usually what people check if it’s not an obvious mistake from my scrubbing this forum.

If you don’t know how to do the above just type in target words in the search or Google them and tediously hit one by one. In my Experience it gets easier.

Good luck!
 

PJS

Active member
If your gain control is changing the volume then it is working. You are either not getting clipping, or the signal is not getting loud enough to clip. D1 to D6 look like different clipping stages, so check them for polarity and connection, and no shorts to anywhere they should be connected. If your signal is not getting loud enough to clip, then I would be looking first at R8/R9 and then R11, R12, C8 and C9. check for the right values, and check for proper connection. It may also be possible that what is coming off Q1 is too soft as well. An audio probe will give you some ideas of where to check. You said you checked voltages against a working pedal. Did you check voltages for Q1 pins?
 

music6000

Well-known member
This is my second build of this pedal. Wanted a larger enclosure so my size 12s could work one or the other stomp switch. Anywho, the gain pot is not working. Dialing it up and down does nothing but increase volume. When the boost is engaged, I get OD, but not without the boost engaged. Checked voltages against my working pedal. Checked the pots and resistance is what it should be. I'm stumped. Attached are a couple of gut shots. Any advice is appreciated. Thanks!

- Chris
What's going on here, Looks like legs could be shorting!
Your other transistor looks like it is close to the Board also, Check that!
Your R1 - 2m2 is 2K2 at the Input to Ground on the bottom right so you may get a Pop from your Footswitch????

What's This.jpg
 
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ProfMagpie

New member
OK, made a signal tracer and have an audio signal through the entire circuit. I have OD on D4 anode, D1 cathode, D3 cathode, and D2 anode. Changed R1 to 2.2M. Pulled C5 and check capacitance...100pF. Transistors and diodes are not shorted or bridged. The IC is a CA3130E. Thanks so much to all of you that chimed in. Hopefully the above info will help.
 

music6000

Well-known member
OK, made a signal tracer and have an audio signal through the entire circuit. I have OD on D4 anode, D1 cathode, D3 cathode, and D2 anode. Changed R1 to 2.2M. Pulled C5 and check capacitance...100pF. Transistors and diodes are not shorted or bridged. The IC is a CA3130E. Thanks so much to all of you that chimed in. Hopefully the above info will help.
How are the 3 Potentiometers mounted under the PCB Board ????
 

music6000

Well-known member
Mounted as normal. All have plastic dust covers.
Good, Are they definitely 10K Resistors, We can't read them!
That 47pf looks crazy Big also????
Solder seems a bit excessive on components as if to much heat on the Soldering Iron caused excess Solder to build around them!!!
Sometimes it's better to Hold off on a Build when you have to substitute non suitable components!
This pedal has been built successfully a number of times over.
 

ProfMagpie

New member
Good, Are they definitely 10K Resistors, We can't read them!
That 47pf looks crazy Big also????
Solder seems a bit excessive on components as if to much heat on the Soldering Iron caused excess Solder to build around them!!!
Sometimes it's better to Hold off on a Build when you have to substitute non suitable components!
This pedal has been built successfully a number of times over.
Definitely 10K resistors and a 47pF film cap...any other thoughts?
 

music6000

Well-known member
...good point, GWK! These incredibly nearsighted eyes needed to take a second look at the backside with a generous dose of magnification. Reflowed some joints on the back and Viola! It's alive! Thanks to everyone for their assistance.
You must have missed the solder pad all together as there is plenty of Solder visible on the component side????
This is why Cleaning the PCB Board is critical to see if all pads are visible for inspection!
 
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