SOLVED Low Tide Modulator - No Output

[BrainDrain]

Built a Low Tide Modulator sometime last year, it didn’t work and ended up in the box of shame. Went through everything I can think of but no luck. It bypasses signal but nothing happens when switched on and the LED doesn’t turn on either. There seems to be voltage coming into the board, I measured at the first diode and it was around 9v.

 

[KR Sound]

So I realized I wasn't getting any voltage in the LM258 (IC4). Pin 8 was reading at zero volts. I jumped the 9v power to pin 8 and it everything worked. Pretty sure I got another PCB with a bad trace. The trace from R69 to C41 on the bottom of the board seems to be broken underneath the layer but can't be seen. When jumped it comes to life. Kinda surprised I got two different PCBs with the same issue.

Weird. Can you scrape off the solder mask and see what’s up? If it’s mid-trace or at the solder pad junction. Bet Robert wouldn’t mind knowing, especially since you’ve had two. Maybe you’re just un/lucky ¯\_(ツ)_/¯

 

[BrainDrain]

Out of the last 35 or so pedals I’ve built I have found 2 bad boards. One was a PPCB board and one was from a private party (although I can’t confirm of it was bad or i messed that one up). It does happen and these companies that make the boards for PPCB and others can and do occasionally have bad runs. I don’t believe it’s super common, but it does happen. Sucks when you KNOW you did everything right… but the level of troubleshooting you go through to find out it was a bad board is often a time to really learn a lot about the circuits etc. so all not lost!!

Yeah it did help me learn something. Just glad I got it out of my box of shame. Although I feel no shame with this one after the PCB itself was bad

 

[BrainDrain]

Weird. Can you scrape off the solder mask and see what’s up? If it’s mid-trace or at the solder pad junction. Bet Robert wouldn’t mind knowing, especially since you’ve had two. Maybe you’re just un/lucky ¯\_(ツ)_/¯

Sorry I already fixed it and boxed it back up before seeing this. It’s a very small connecting trace.

 

[comradehoser]

You're showing us the jumper to pin 8, right?

Just to be clear--you had two low tide boards with bad traces--one to pin 8 and the other r69-c41?

I was looking at the schematic... R69 is connected to C41?

I see that they both connect to VCC but in my reading it doesn't look like they are directly linked/part of the same subcircuit without intervening components. But also, that might be my schematic dyslexia/noobularity. And is it part of the same issue? C41 looks like it's part of the power circuit for IC3, not 4. Me confused.

 

[BrainDrain]

You're showing us the jumper to pin 8, right?

Just to be clear--you had two low tide boards with bad traces--one to pin 8 and the other r69-c41?

I was looking at the schematic... R69 is connected to C41?

I see that they both connect to VCC but in my reading it doesn't look like they are directly linked/part of the same subcircuit without intervening components. But also, that might be my schematic dyslexia/noobularity. And is it part of the same issue? C41 looks like it's part of the power circuit for IC3, not 4. Me confused.

I only had one defective Low Tide board. I know of someone else who had 2 though. No idea if it was the same issue as this though. Could definitely be something unrelated. The other defective board I had was the Dirt Dauber. Both had the same kind of issue. Frustrating but both an easy fix so no worries. The layout of this pcb and shematic is a bit confusing to me too. The voltage looks like it goes through D4 then down to C32 and from there to R69. It then jumpers from R69 (defective jumper is circled in pic) to C41 and then powers IC4, the LED and Q5, etc from there. Also The picture of the pcb in the webstore doesn’t show all the traces if that’s what you were looking at. And There’s a separate power trace running from R69 to the IC3. It runs under that long row of resistors. As for schematics I’m too new to understand the complicated stuff but it helped having it in this case.

 

[comradehoser]

I only had one defective Low Tide board. I know of someone else who had 2 though. The other defective board I had was the Dirt Dauber. Both had the same kind of issue. Frustrating but both an easy fix so no worries. The layout of this pcb and shematic is a bit confusing to me too. The voltage looks like it goes through D4 then down to C32 and from there to R69. It then jumpers from R69 (defective jumper is circled in pic) to C41 and then powers IC4, the LED and Q5, etc from there. Also The picture of the pcb in the webstore doesn’t show all the traces if that’s what you were looking at. And There’s a separate power trace running from R69 to the IC3. It runs under that long row of resistors. As for schematics I’m too new to understand the complicated stuff but it helped having it in this case.

I was looking at the schematic itself--it's not clear there how r69 and c41 are connected. I see the trace, though.

Are you sure it's not powering IC3 (the big one)? c41 is close to IC3 and pretty far from IC4. The schematic also shows c41 in a circuit with IC3. IC3 then routes to IC4 via a whole bunch of stuff. Looks like maybe "VREF LPG" and most likely "LPG Control" in particular were what was being affected since LPG Control makes an appearance in IC4?

I have no idea what those are though. LPG= Low Pass Gate?

If you're happy with it being fixed, you could mark the thread solved. I'd be interested to understand why it's working and what, if anything, your jumper bypassed or addressed.

You are building the "big" version, right? Not the mini.

 

[BrainDrain]

I was looking at the schematic itself--it's not clear there how r69 and c41 are connected. I see the trace, though.

Are you sure it's not powering IC3 (the big one)? c41 is close to IC3 and pretty far from IC4. The schematic also shows c41 in a circuit with IC3. IC3 then routes to IC4 via a whole bunch of stuff. Looks like maybe "VREF LPG" and most likely "LPG Control" in particular were what was being affected since LPG Control makes an appearance in IC4?

I have no idea what those are though. LPG= Low Pass Gate?

If you're happy with it being fixed, you could mark the thread solved. I'd be interested to understand why it's working and what, if anything, your jumper bypassed or addressed.

You are building the "big" version, right? Not the mini.

IC3 is being powered from from the same point on the pcb as IC4. Power comes down from D4 to C32 and then to R69. On top there's a trace that goes from R69 to IC3 and on bottom of R69 is the trace that connects over to C41. From there it powers the left side of the board. I'm not sure how it plays out on the schematic but if you had the PCB in front of you it would be easier to see. And yes it's the regular version not the mini. I was going to mark it solved but wanted to wait a few days just in case I'm wrong and someone figures out what I did to make it work

 

[BrainDrain]

I'm having the same issues as you, no output but bypassed signal passes through fine. I did come across this schematic somewhere deep in the forums though, might be helpful:


View attachment 67623

Thank you for adding this to the discussion. I searched but couldn't find it. It really helped a lot.

 

[BrainDrain]

So I thought I had this one solved but only had it half solved. The trace I fixed took care of the power issue and now the pedal works and sounds almost as it should. I came back to it recently and realized the only thing that doesn’t work is the Gate. I read all the threads on how to set it but I’m getting no response from the trim pot or Gate pot in any position when using the methods that were listed. The trim pot and gate pot are both good so that can be eliminated. Any idea what would cause both to not work at all? Hopefully it’s not another broken trace somewhere.

 

[BrainDrain]

So I did some more poking around with the DMM and figured out it was yet another broken trace. Attached a jumper and like magic the gate works. Looking at the schematic the Jumper goes from the left side of R46 to the junction where R67 & R68 connect. There was zero continuity between those points. After I found the first bad trace months ago I started checking the traces on all pcbs before building. I just like to eliminate it from the beginning now. Guess I can mark this one “solved” finally Thought this one was gonna end up a cold case.

 

[Matopotato]

FWIW: I have adopted a way of working to check the legs after soldering and before cutting. I DMM from a leg to the points in the schematic where they should go. Tedious? Yes. Do I find any bad soldering points or broken traces? Some, not a huge deal, but after some earlier larger builds I found that troubleshooting to be more tedious than the method above.
Also in some strange way I feel I get to know the circuit a touch better. But that is probably just in my own mind