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PostPosted: Sun Sep 25, 2022 5:13 pm 
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I built a Brownface Trem pedal and it worked nearly perfectly right away. The only problem was that there was some noise-- a little pulsation and some whining rotation noise, not terrible but there. I tried moving wires around with my thin screwdriver (bad I know) and believe I shorted the (+) and + DC jack connections together. Ever since then, no LED lights up and the pedal doesn't work anymore.

I didn't post pics because I don't think there is anything to see as it was working just fine other than some mild noise. Does anyone have any idea what I may have blown by shorting the (+) and + on the DC Jack that would now be preventing the pedal from working? I'm hoping there is a part that I can replace and be back up and running.

More info: I was powering it with a Volto 9V external battery pack that plugs into the DC Jack. I also added a pic even though the pedal worked fine until I shorted it.

Thanks in advance for any help!


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PostPosted: Mon Sep 26, 2022 11:36 am 
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Transistors generally don't fry as easily as something like an op amp. So, while it is a definite possibility that you did damage one or more of the semi conductors, I'd be more inclined to suspect that you just pulled one of your wires loose. If that cloth covered wire is solid core, there's a good chance that the wire is broken inside. Or maybe you damaged your power supply.

Do you have a multimeter and do you know how to read voltages?

Also, the noise you were initially experiencing may have been caused by your power supply. I'm not really familiar with the Volto or lithium Ion power supplies. But usually noise problems like this originate with the power supply.

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PostPosted: Mon Sep 26, 2022 12:33 pm 
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Actually the cloth covered wire is stranded. I heard a loud click through the speaker when I touched the two together and then death. I don't think I really moved the wires at all and they seem to be in tact and the solder connections are good. I also tried a different battery and the pedal is still dead.

I do have a volt meter. Is there a way to measure / test transistors in place in the circuit? Or are there any other measurements I can take?

Thanks so much for the help with this self-caused problem!


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PostPosted: Mon Sep 26, 2022 1:38 pm 
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Image

Q1 is the transistor in the lower left hand corner closest to the battery snap. What are the voltages for the emitter, base, and collector?

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PostPosted: Mon Sep 26, 2022 1:44 pm 
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Just in case you're not sure how to take a DC voltage measurement:

To measure DC voltage levels, set your multimeter to the DC voltage mode, indicated by a solid line above a dotted one. Use the 20VDC range setting if it's not an auto-ranging meter. Your power source needs to be connected and there needs to be a cable in the input jack. If the pedal is assembled into the metal enclosure, put the black probe into one of the corner screw bosses of the enclosure--this is your ground connection. If the "guts" are out of the enclosure, use the sleeve tab of the input jack for the ground connection. Then touch the red probe to the point that you want to measure.

The way Q1 is oriented on the PCB, the collector is the bottom leg, the emitter is the top one and the base is in the middle.

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PostPosted: Mon Sep 26, 2022 5:09 pm 
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I measured with the pedal connected to a combo amp and a different Volto battery, just to make sure things were connected correctly and the battery was working properly. I can tell when the pedal switch is engaged because if I turn up the DEPTH control the volume output gets quieter. Turning the DEPTH knob down raises the level as it must be acting like a mix control giving more clean signal as it's turned down.

I got the following:

emmiter: 2.832V
base: 3.126V
collector: 9.04V

Any indications here?
Thanks!


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PostPosted: Mon Sep 26, 2022 5:44 pm 
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OK, the first thing that confirms is that power is getting into the pedal. Also, those voltages look good for Q1, so so far, so good.

I'm guessing that whatever you did blew the LED. Since the LED is a part of the effect circuit (unlike most BYOC pedals), try replacing it and see how the pedal responds.

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PostPosted: Mon Sep 26, 2022 9:16 pm 
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duhvoodooman wrote:
OK, the first thing that confirms is that power is getting into the pedal. Also, those voltages look good for Q1, so so far, so good.

I'm guessing that whatever you did blew the LED. Since the LED is a part of the effect circuit (unlike most BYOC pedals), try replacing it and see how the pedal responds.


Ah, good to know about the LED being part of the circuit. I will try replacing it and see what happens. I have some random LEDs laying around. Not sure about the rating on them other than a larger LED that says 9-12 V. Is that OK just to try, or maybe a 1N4007 diode, just to test?

Thank you.


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PostPosted: Tue Sep 27, 2022 9:47 am 
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chknpicker wrote:
Ah, good to know about the LED being part of the circuit. I will try replacing it and see what happens.

If you look at the BFT schematic, you'll see in the lower left that the LED is part of the speed control portion of the circuit. Since the C19 cap blocks any DC flow between that section and the rest of the effect circuit, the only voltage source for the speed control circuit is what comes through that LED. I don't understand the workings of the BFT circuit well enough to know if the failure of that LED would render the entire effect circuit mute or just disable the speed modulation control (I suspect it's the latter). But if it's blown, it needs to be replaced in any case.

chknpicker wrote:
I have some random LEDs laying around. Not sure about the rating on them other than a larger LED that says 9-12 V. Is that OK just to try, or maybe a 1N4007 diode, just to test?

If you have any 5mm LED's or the smaller 3mm LED's on hand, you can use either of those. I wouldn't bother with anything else.

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PostPosted: Tue Sep 27, 2022 12:19 pm 
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Y E S S I R ! ! ! :D The LED was indeed blown. I replaced it and she works like a champ!

Thanks so much for the troubleshooting help! It's good to be back up and running again.


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PostPosted: Tue Sep 27, 2022 12:37 pm 
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Ah, excellent news! Glad that it turned out to be that simple. :mrgreen:

Just to close the loop on the likely cause of the blown LED: I suspect that while fiddling around with the screwdriver, you accidentally shorted the cathode (round solder pad) of the LED or the top eyelet of the adjacent 10K resistor directly to ground. That resistor limits the current flow through the LED, and shorting the cathode directly to ground ahead of that resistor will cause the LED to blow in a fraction of a second from too much current through it. Many BYOC pedal builders have discovered this fact by "testing" an LED by touching the two leads to the terminals of a 9V battery. And it confirms that the LED works....very briefly! (Don't ask me how I know this.... :oops: )

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PostPosted: Tue Sep 27, 2022 1:15 pm 
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That's probably exactly what I did. Makes sense. Thanks for the explanation.


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