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PostPosted: Sat Jul 02, 2022 5:34 pm 
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This is my first build and I am learning to troubleshoot, so any help is greatly appreciated.

This pedal has dry signal when the pedal is on or off, but there is no delay. From reading other threads, trimpots seem to be a consistent issue, and I confirmed that they are in the right spot but beyond that I am not sure the best way to troubleshoot. I also pulled some voltages from another thread and have written mine in to help with diagnosis. Most of the voltages look close, although pin 1 and 7 of the 571 chip are outliers. Pin 1 is also strange, in that it initally reads at around .66 volts, and then settles down to .44 volts.

Any ideas on what the issue might be?


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PostPosted: Tue Jul 05, 2022 11:05 am 
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What is your power supply? I'm assuming you're using a battery that is probably about to die.

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PostPosted: Wed Jul 06, 2022 7:31 am 
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Those were actually measured with a power supply (which reads right at 9V).

One other thing to mention -- when I first powered it up, I accidentally swapped the (+) and + connections on the AC adapter jack. I don't think that would fry anything, but wanted to say something just in case.


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PostPosted: Wed Jul 06, 2022 10:31 am 
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How many amps is your power supply rated for? Reversing the polarity is usually instant death to dual op amps. Especially the 4558. But this PCB has a reverse polarity protection diode. It's not always 100%, but we can assume your 4558 is still good because if it wasn't, you wouldn't be getting any dry signal. The chip itself would also be getting extremely hot.

Aside from being just a little low, your voltages all look okay. A signal tester would be a big help in pinning down where your signal is dying. You wouldn't happen to have one of those handy, would you?

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PostPosted: Wed Jul 06, 2022 3:16 pm 
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Just noticed that one end of a resistor doesn't appear to be soldered, the hole looks empty from both sides. As viewed from the component side, it's just above the LED on the right, next to the little ceramic cap, and at the corners of two red poly caps. I'm not familiar with the circuit, but generally all components require soldering :wink:

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PostPosted: Wed Jul 06, 2022 3:30 pm 
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Yes, it's probably also a good idea to do a reflow of all your solder joints on the PCB as well.

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PostPosted: Thu Jul 07, 2022 7:33 am 
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Doh! Thank you for catching that missed connection.

I soldered that missing connection, and reflowed most of the joints (I didn't do the harder to reach connections under the pots yet). Unfortunately I still have the same result.

By signal tester, do you mean an oscilloscope? I don't have one of those, but I can generate a tone and use my multimeter to follow the signal. I think I have a good idea of how to do that using the schematic and pcb mapping, although I haven't actually done it before so any pro tips are appreciated.


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PostPosted: Thu Jul 07, 2022 10:45 am 
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Well, yes, you can use a signal generator and an oscilloscope. That's generally how it's done in a more "professional" manner. The signal tester is more of a "down and dirty" kinda budget DIY thing. It's nothing more than a probe that connects to your output cable to bypass signal from various test points on your PCB directly to your amp. You plug your guitar into the input pf the pedal and strum it while you test.

http://byocelectronics.com/signaltesterinstructions.pdf

Here's a link to the instructions for the kit we sell (which is out of stock), but it's pretty easy to make one from stuff you probably have laying around. Everyone probably has a flaky cable in a box in the closet somewhere. Cut the plug off the end that is flaky. Strip that end to expose the shielding and the "hot" conductor. Connect a wire to the shielding so that you can ground it to the pedal's ground. In the kit, we use an alligator clip, but there are probably many ways to skin this proverbial cat. Then connect a capacitor to the "hot" wire. It can be pretty much any cap. .1uF to 10uF is ideal, but even a tiny 100pF cap will work, it just won't pass very much low frequency. Connect one end of the cap to the hot wire. The other end of the cap is your probe. You can literally use the cap's lead as the probe. Just tape up the other end of the cap real good so that it doesn't short out when you touch it.

You mostly want to know if you're getting signal at the input of the BBD (pin 9 of the 3205) and the outputs (pins 6 and 7). You're voltages suggest the 3205 and 3102 are working, but based on experience, it's the most likely part to fail.

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PostPosted: Thu Jul 07, 2022 4:45 pm 
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That is great--thank you! I won't be able to get to that until the weekend, but that all makes sense.


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PostPosted: Fri Aug 12, 2022 3:21 pm 
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It took me awhile to get back to this, but I think I found the problem. The bias trimpot only passes signal above 1:00 or so. Below that point, there is nothing and then it just kicks in at 1:00. at 1:00 it does sound a little too hot to me, and I would to run it lower.

I assume that this is just a bad trimpot. Any thoughts on what else it could be, or should I just go ahead and replace it?


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PostPosted: Fri Aug 12, 2022 6:42 pm 
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I would test the trimpot resistance with a multimeter before replacing it, since it's possible to have voltage bias settings that don't pass signal (though I don't know if that's possible in this particular circuit). Measure the resistance between the middle lug (wiper) and each of the outer lugs at several different positions of the trimpot sweep. The resistances should continuously change on both sides of the wiper if the pot is operating correctly.

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PostPosted: Mon Aug 15, 2022 5:48 am 
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Great idea--I did do that and it and the resistance does change consistently throughout the sweep, so the trimpot seems good. It is a 10K trimpot that is reading about 7.5K, so presumably on the outer range of the manufacturing tolerance which probably makes a difference (the instructions suggest starting with the trimpots at noon, but this doesn't pass any signal until 1:00, which is what makes me think this pot is behaving a little out of the norm).

Either way, I did some more trimpot tweaking, and gigged with the pedal yesterday. It sounds great! An awesome pedal and a great forum. Thank you all for the help.


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