Build Your Own Clone Message Board

This is my fourth build and it hasn’t quite fired up just like the others. Still very green at this, and my troubleshooting needs some help. The bypass works, the LED lights up, but there isn’t any noticeable change to the guitar’s sound (besides raising and lowering the guitar’s volume when I turn the trimpot to different spots). I’ve messed around with the trimpot and the pots, but nothing. At times there’s a bit of static, and I thought I heard the effect once or twice, but definitely nothing consistent.

At first I thought I had got the pots weird backwards, but they look right to me. I reflowed the solder on the PCB, and I checked to make sure nothing was backwards. But I don’t have an eye for this and it could be something obvious.

My other thought is that I damaged a part while I was soldering, perhaps the IC. I don’t know what happens exactly if you do that.

I’ve looked at the other threads and it seems like other people were experiencing similar problems, but the solutions were either difficult for me to understand (I’m not good with a multimeter, though I have the one BYOC sells) or didn’t apply to my build.

Any help would be greatly appreciated!





I just noticed that the second picture is a bit blurry. I can take another if it would help with the diagnosis.

Thank you!

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Ryan

If tweaking the trimmer makes the volume change it seems like your pedal is more than half working. The problem would seem to lie in the envelope follower part of the circuit.

This uses the 741 op-amp to boost the guitar signal then T3 T4 T5, D2 D3, C9 and the various bits around them (these form a full wave rectifier) turn the boosted signal into a voltage that follows the instantaneous volume of the input note. This voltage is applied to T6 to do the same thing that tweaking the trimmer does, but following the guitar note rather than the rotation of your screwdriver on the trimmer.

So the signal needs to get through VR1 to feed the input of the op-amp and then out of the op-amp to feed the full wave rectifier. Check you have VR1 connected properly and that C2, R10 and R18 are all properly soldered.

If you set your multimeter to the 20V DC range and connect your black lead to the effect metal case, or if you have it completely out of the case, to the sleeve terminal of the input jack socket, carefully touching the red probe to pin 7 of the 741 should show just under 9V and on pin 6 you should see about 4.5V. If you have, or can build, an audio probe you should get quite a loud version of the pedal input signal on pin 6 of the op-amp with the Sensitivity turned up.

If you get that far and everything checks out you know you have signal at the input of the full wave rectifier so the fault is in the rectifier somewhere. Lets leave it there for now and see how you get on...

Thank you so much for your lengthy reply, Tark!

I was able to follow what you said, which is definitely a credit to your ability to explain things.

My solder joints look okay, and I reflowed those that could've been questionable. However, when I apply the voltmeter to the IC, no voltage is registered at any of the pins. I checked to make sure I had it set and grounded correctly by checking the voltage of the battery, which it read fine. Does this mean that my op amp was burned while I was soldering, or is there perhaps a short somewhere?

Thanks again for your time and help!

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Ryan

Did you have a plug in the input jack when you took your readings?

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"It’s your soldering."

As Steven says you would need a lead, or at least a jack plugged in to the input jack, to actually have battery power applied to the circuit.

If you did have a jack in the input and you still got no volts on the 741 you should check R19 a 1K, very carefully for bad joints. The 741 gets its positive supply through that resistor. One end of that resistor goes to the 9V battery supply and the other to the 741.

No I did not. Wow, that's obvious, but I didn't even think of it.
Okay, I got 8.1V at pin 7 and 4.2V at pin 6. Less than what you said there would be, but I assume that it's enough to tell that it isn't the problem.

At this point, should I assume that I have a bad solder joint someplace, even if they look okay to my untrained eye?

There is a bit of flux on the solder side of the board. I've seen people on this board suggest that you wipe it off with acetone. What problems can excess flux cause?

Thank you guys!
Ryan

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Ryan

Okay, I reflowed the solder for VR1, and now if I have the sensitivity and the trimpot at the right spot, it does produce a swell, though it is quick. If I move the sensitivity all the way clockwise, the effect disappears.

I suppose that I probably have a bad solder joint somewhere still.

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Ryan

I used a toothbrush and acetone to wipe off the flux and reflowed again afterwards, since it revealed some un-shiney joints.

And it works!

Another thing I that was confusing me was the Sensitivity knob--the effect doesn't seem to be noticeable if it's full clockwise (I assume it's because the volume difference between the beginning and ending of the swell is the same). If anyone like me--that is, embarrassingly new at this--is reading this and having the same problem, try pulling back the sensitivity to about noon.

I'm still curious, though, what can excess flux do to the PCB? I mean, it isn't conductive, is it?


Thanks again for all your assistance, I would've probably given up otherwise!
Ryan

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Ryan

Well that's the problem, excess flux, particularly when carbonised IS slightly conductive, and it is slightly corrosive.

Most reputable electronics manufacturers wash their PCB's in solvents after soldering to remove the flux. On a lot of the cheap Chinese products they skip that step.

It is only really a problem with circuits that are high impedance and very sensitive to leakage currents.

I would NOT recommend using acetone if you can avoid it, it is too likely to dissolve any plastic parts on components such as capacitors for example. You can also get a headache or even brain damage from breathing the stuff.

Isopropyl alcohol seems to work well on most fluxes, doesn't dissolve components quite so readily and it doesn't smell quite so strong. Several applications can be required, use just a quick splash and it dissolves the flux and then distributes it as a sticky coating over the whole surface. Big patches of flux can be carefully chipped off with a toothpick and the flakes brushed off before using the isopropyl to really clean things up.

Great to hear you got your pedal working BTW.

It is possible that if you turn the Sensitivity all the way up it overloads the envelope follower and the volume swell gets stuck in quiet mode for a while.

Ah, thanks Tark. See, this is information that is extremely useful for someone like me. I've read quite a bit of material on this forum and other places about pedal building, and I never saw anything about flux being conductive or the best way to go about cleaning it up.

I think I'll pick up some isopropyl alcohol today. Just one other thing: do you have to wipe off the flux after you've splashed it with the alcohol?

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Ryan

Basically yes.

The isopropyl dissolves the flux so it is best to wipe it off or get it to run off before it dries. You can use a Q tip or several, damped in iso for local cleanup.

I like to use the stronger Isopropyl from the drugstore (or my tech grade stuff) and a toothbrush. A couple applications and scrubs, and she's all nice and clean

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Brilliant. Stuff like this is tough to figure out on your own. I'm always worried that I'll do something that'll damage the components and the board.

In fact, thinking about that, I have another question. I know, I know... I said that was the last one, but it'd be a shame to start a whole new thread.

So, which components can be damaged by the heat while their being soldered? Transistors and ICs? Is it a good idea to use sockets for those? What exactly will happen if a part is overheated? Will it simply not work and break that part of the circuit?

I really appreciate all the tips and help--this community is amazingly supportive. Much different from most of the internet.

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Ryan

All commonly available components today are designed to withstand the soldering process, so really the general answer to your question about which components can be damaged is - none of them.

However this assumes that a good soldering technique is used so that the heat shock is minimised. If for example you used a soldering iron that was too cool or could not provide the necessary thermal transfer to the joints you might actually end up holding the soldering iron in place on the joint for longer than necessary while you tried to get it up to temperature so that the solder would flow properly. This would give heat a chance to penetrate through the joint and into the component. Some people new to soldering attempt to use a soldering iron like a brush, first loading it with solder and then making multiple attempts to dab that onto the joint. Apart from being the wrong way to do things this can also lead to the joint being heated for longer than necessary.

While components like resistors and capacitors can be mounted flush against the top surface of a PCB I've noticed some people seem to try to push transistors and FETs as close to the board as they can get. This isn't necessary, they can be left sticking up a bit and the extra length of lead will help protect them from overheating during soldering. ICs can be soldered in, but it is much safer on home built kits to use sockets. They protect the ICs from heat and often make fault finding much easier.

The most problematic component with the BYOC kits seems to be the switches and particularly the foot switches. Inexperienced builders seem to really struggle with wiring these neatly and overheating during soldering can melt the glue that holds the tag/contacts in place and possibly melt internal mechanical parts of the switch.

In the old days of germanium transistors the transistors were rather delicate and could easily be overheated, which is why you see that most kits that have germanium transistors have sockets for them.

Lastly the wire that BYOC provide has a purple insulator that melts really easily.

Ah, thank you! That answers some questions I've had for a long time. It is definitely reassuring to know that there's no danger of overheating the components as long as you solder correctly. I haven't used sockets yet, but the benefits do seem to outweigh the $.75 cost.

You even answered a question that I had, but didn't ask. I knew that resisters could be put flush against the PCB, but I wasn't sure about the capacitors or the transistors.

The more I learn about building, the more I love it.

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Ryan

better than shaving, anyway?

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Haha, exactly! But that goes for just about anything..

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Ryan