Leprechaun has clean sound no matter what.

deladonut

New member
Hey all, just working on a Leprechaun build and when I’m plugged in and powered I get a clean signal no matter what state either switches are in. The knobs appear to do nothing as well. Just a clean tone all around. Both LEDs work. Anyone seen this before? I’m randomly re-soldering pads and trying to make sure the FV1 is soldered correctly. Not sure where to start with this one...

F5BCD434-90E0-4C2D-8642-8450691521B2.jpeg
 

Nostradoomus

Well-known member
Scrub your board down (top and bottom) with some isopropyl alcohol and a toothbrush, especially around the Fv-1 to see if maybe there’s a bridge there somewhere.
 

PJS

New member
I would measure the power supply voltages to all your ICs just to make sure they are all getting correct power. Then measure (with power off) the bypass switch contacts. Make sure all the contacts connect properly, and switch over properly. These switches are pretty sensitive to soldering heat and it can be pretty easy to get it stuck one way or the other.
 

zgrav

Well-known member
I suggest removing it from the enclosure to clean the board with IPA, and then clean both sides. also take a detailed picture of the other side to post if your board is still not working.
 

Mcknib

Well-known member
As Chuck often says a visual inspection under magnification reveals a lot incorrect values dry joints etc

I usually check I've got power and ground first then check offboard wiring to make sure I've not got my out going to my in etc

Then I check all values and orientation are correct which I also do when trying to assist

Anyway no schem so don't know if the dry signal has a separate path to out and is eventually mixed

Zoomed into your pics to check values but not sure what I'm seeing on your FV1 is it slightly burnt or just the light playing tricks?

It looks like you've a few solder bridges especially around pins 18, 19, 20 and 26, 27, 28 but as I say may just be the glare from the photo lighting

Screenshot_20200920-134048_Chrome.jpg
 

deladonut

New member
Spent a fair amount of time on this board and the only thing I can come up with is that the FV-1 doesn't work. Voltage regulator is working and I have 3.3v at all the correct locations. All grounded locations are correct. I've traced nearly every point on this board using this schematic I found in another thread:
PedalPCB-Leprechaun.jpg
I
I've cleaned the board several times now as well, swapped the TL072 ICs just to make sure one wasn't bad, tested both 3pdt switches and found them to be correct. Based on the schematic, it would make sense that if the FV-1 was bad, I'd be getting a dry clean signal with no blend control. At least that's what I can tell, unless someone else has any ideas. Maybe I'm missing something?
 

Mcknib

Well-known member
I'm taking it the weird looking surface on the chip is just a shadow or something I don't know you haven't said

If you haven't already with no power to the pcb continuity check all the pins with the schematic make sure there's not continuity where it shouldn't be

I've had bridges I couldn't see even with a magnifier, that I only found with a continuity check

If you have an audio probe even better check if audios going in and out of the FV1 if not you can go back to find where audio stops

Even though it's frustrating as hell you'll get there eventually
 

zgrav

Well-known member
use an audio probe to see if sound is reaching the FV-1 on pins 1 and 2. then see if sound is leaving it on the last 2 pins. it looks like your fv-1 may have had some heat issues based on what look like deformations in the top of it, but I hope you can find a different solution to get it working.
 

deladonut

New member
I get sound to pin one, no sound out of pin 28. The picture I posted looks like I toasted the IC but it was just dirty with flux
image.jpg
 

zgrav

Well-known member
I might try lightly touching up all the pins on the FV-1 to see if they would clean up better with alcohol and a toothbrush. if it is a bad chip, you won't hurt if by doing that. and it may be that it could make a difference. from posts on the forums, there have been a higher number of bad FV-1 chips recently.

what was the source for this FV-1 chip?
 

deladonut

New member
I might try lightly touching up all the pins on the FV-1 to see if they would clean up better with alcohol and a toothbrush. if it is a bad chip, you won't hurt if by doing that. and it may be that it could make a difference. from posts on the forums, there have been a higher number of bad FV-1 chips recently.

what was the source for this FV-1 chip?

I’ll try scrubbing and maybe heating the pads again. I got this one from small bear. Kind of bummed to hear there’s been some bad ones lately. Oh well. I’ll keep trying though! Not ready to give up quite yet.
 

zgrav

Well-known member
Usually it is some relatively minor build issue instead of a chip, or maybe a wrong part value used on the board. If you search through the forms for recent posts about FV-1 chips you'll find the threads about a few bad ones.
 

Chas Grant

Active member
Its hard to tell due to all the flux but it looks as if pins 8 and 9 have a solder bridge. All the flux remaining needs to be removed, not only so you can see what's going on with the FV-1, but it is also mildly corrosive and can cause issues with the circuit at a later time.
 

Mcknib

Well-known member
Perhaps post the voltages on your TL072s that may reveal something

I know very little about the FV1 there was a troubleshoot recently where the CD4069 was at fault you could check to see if you're getting a clock pulse from pin 4 of the CD4069 and at pin 9 of the FV1

If your meter has a Hz function use that the tracking pot should alter it as you turn it, or measure the voltage see if it changes at different pot settings or if the voltage oscillates

I know you can get problems with the 'normal' crystal on the FV1 so I'd imagine If the 4069 oscillator doesn't work it'd be a problem

But as I say my knowledge is scant at best perhaps Mr ppcb Robert can advise

Worth checking anyway then you can rule that out
 
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