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.

 

[jimilee]

What are you getting at your regulator?

 

[BrainDrain]

What are you getting at your regulator?

I'm getting around 8.1v on one side and around 5v on the other. Zero volts in the middle. Using a battery off my bench that's around 8.65 volts.

I swapped out all of the ICs except for the one that came with the PCB. If somehow there were something wrong with that IC I feel like the LED would still work but I really don't know enough about this circuit. There doesn't seem to be a schematic for this build in the doc.

I guess it's possible there's a bad component somewhere or maybe I fried one of the smd jfets when soldering it in. The only other time a pedalpcb board didn't work for me it ended up being a bad trace in the PCB. The board looked completely fine but there must have been a tiny spot with a broken connection under the top layer. I just ran small jumper around the spot and it works fine now.

 

[Jimi00]

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:

 

[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

A builder I follow on instagram built two of these and neither worked. Starting to think I'm having the same issue as the other defective PCB I got with the bad trace. Or maybe something is up with the included randomizer IC? I feel like the bypass LED would still work even if there were an issue with that IC though. Gonna try the audio probe and see if I can find anything. Guessing not too many are interested or know much about this circuit?

In the above schematic does anyone know which resistor the CLR is? R54 or R55? Just wondering why there's an extra resistor there.

 

[KR Sound]

Hmm. Mine fired right up with no issues. Unfortunately I sold it so I can’t get any IC voltage readings for you. Here’s a pic if it helps any.

 

[benny_profane]

In the above schematic does anyone know which resistor the CLR is? R54 or R55? Just wondering why there's an extra resistor there.

They both are. The cap is there as an anti-pop measure by mitigating inrush current. Both should be at least 2k2, but they can be bigger.

 

[Mcknib]

Did you get all your ICs from reputable suppliers

All your component values and orientation that I can see look correct I can't fully see R49 the 1M which forms a voltage divider for Q3 with R48

I've no clue how it all works but I'd suggest getting the audio probe out now that you've got the schematic

I'd start at the IN pad to make sure audio's actually getting in then I'd probe the outputs of active devices Q1 drain Q2 emitter IC4 pin 7, IC7 pins 7 and 8 etc to see if you can find where it drops out and at the same time see if you have indeed fried anything If you get no audio then trace back to that device input and preceeding components

If you get no signal on the mix pot lugs 1 and 3 then I'd suspect no dry signal is getting through either route from Q2 emitter where as you can see it goes 3 ways up top to the gate thing, through the middle for wet and down below for dry I think

But as I say I've no clue, and when I've no clue, which is often, that's what I do

 

[BrainDrain]

Did you get all your ICs from reputable suppliers

All your component values and orientation that I can see look correct I can't fully see R49 the 1M which forms a voltage divider for Q3 with R48

I've no clue how it all works but I'd suggest getting the audio probe out now that you've got the schematic

I'd start at the IN pad to make sure audio's actually getting in then I'd probe the outputs of active devices Q1 drain Q2 emitter IC4 pin 7, IC7 pins 7 and 8 etc to see if you can find where it drops out and at the same time see if you have indeed fried anything If you get no audio then trace back to that device input and preceeding components

If you get no signal on the mix pot lugs 1 and 3 then I'd suspect no dry signal is getting through either route from Q2 emitter where as you can see it goes 3 ways up top to the gate thing, through the middle for wet and down below for dry I think

But as I say I've no clue, and when I've no clue, which is often, that's what I do

Thanks to everyone for the replys. All ICs came from reputable suppliers. Either Mouser, Small Bear or Stomp box parts. The LED not working is throwing me off a bit. I've seen pedals not work before but the LED still turned on.

 

[KR Sound]

Have you tested the footswitch with a DMM to make sure everything is good there?

 

[BrainDrain]

Yeah the foot switch is good too.

 

[comradehoser]

The bypass LED is of no significant diagnostic value because it is not a functional part of the main circuit. It can light up or not light up and it won't matter at all to the signal and its processing.

What you'll want to do is do a systematic probe of voltage with power (at the jack, diode, and then all the pins of the ICs in order--I do transistors too), continuity, or audio (without power) along the schematic starting at the in jack tip. You might end up doing all three. I usually try to be really thorough with continuity and audio to rule out possible problems systematically, so I start at the very beginning of the schematic and work through every single component/connection until I get to the outs. It might seem like overkill, but it beats skipping around trying to find the problem and then forgetting what you did. I usually use a highlighter to mark the path that I've tested as I test.

 

[Bio77]

My bet would be a foot switch or wiring problem. I'd check continuity from your input/output tips to the board point. Also from input/output tips the ins and outs of the PCB in the on position. Then test continuity between the FS pins in both positions. The LED not lighting up is constant with something wrong there. I've overheated a few foot switches before and had continuity in one position but none in the other. I’ve also crossed input and output wires, which will work in bypass but not when the PCB is engaged.

 

[Giorfida]

The bypass LED is of no significant diagnostic value because it is not a functional part of the main circuit. It can light up or not light up and it won't matter at all to the signal and its processing.

What you'll want to do is do a systematic probe of voltage with power (at the jack, diode, and then all the pins of the ICs in order--I do transistors too), continuity, or audio (without power) along the schematic starting at the in jack tip. You might end up doing all three. I usually try to be really thorough with continuity and audio to rule out possible problems systematically, so I start at the very beginning of the schematic and work through every single component/connection until I get to the outs. It might seem like overkill, but it beats skipping around trying to find the problem and then forgetting what you did. I usually use a highlighter to mark the path that I've tested as I test.

Normally I agree about the LED not being helpful, however just recently it helped me diagnose a cracked trace in a PCB. It was a dual drive pedal, and one side worked and the other didn’t. lLED wouldn’t light on the one side. Turns out only half of the board was seeing the +9v. Bussed a wire and it fixed the problems.

 

[BrainDrain]

My bet would be a foot switch or wiring problem. I'd check continuity from your input/output tips to the board point. Also from input/output tips the ins and outs of the PCB in the on position. Then test continuity between the FS pins in both positions. The LED not lighting up is constant with something wrong there. I've overheated a few foot switches before and had continuity in one position but none in the other. I’ve also crossed input and output wires, which will work in bypass but not when the PCB is engaged.

Footswitch and wiring is good. It seems like part of the PCB isn't getting voltage.

 

[BrainDrain]

The bypass LED is of no significant diagnostic value because it is not a functional part of the main circuit. It can light up or not light up and it won't matter at all to the signal and its processing.

What you'll want to do is do a systematic probe of voltage with power (at the jack, diode, and then all the pins of the ICs in order--I do transistors too), continuity, or audio (without power) along the schematic starting at the in jack tip. You might end up doing all three. I usually try to be really thorough with continuity and audio to rule out possible problems systematically, so I start at the very beginning of the schematic and work through every single component/connection until I get to the outs. It might seem like overkill, but it beats skipping around trying to find the problem and then forgetting what you did. I usually use a highlighter to mark the path that I've tested as I test.

I agree that it might not be of value in most cases. That's what I was getting at when I said I had seen pedals not work but the led still did. In this case the LED not working at all when I give it ground must mean it's not getting voltage. It seems like part of the pcb isn't getting any. Gonna try the probe today. Thanks for the input

 

[comradehoser]

Sure, status LEDs lighting/not lighting is information, but can also be the result of issues totally unrelated to the signal and it's processing in the circuit (i.e.: a burnt out LED, bad solder on the 3pdt switch, etc). Other than power supply, it's not directly relevant to the main circuit and won't tell you anything about issues in signal processing there--whether it works or doesn't work doesn't affect anything at all. Proof is I've stopped putting LEDs in 90% of my builds because it's my least favorite part of building until I audition the pedal as a keeper. Obviously this doesn't apply to LEDs within an LED/LDR array that are functional in LFOs or what have you.

@BrainDrain if you suspect a problem with current, then you can plug the pedal in, connect one end of your multimeter to a pedal ground, and probe and write down all voltages at the IC and transistor pins (since you've already done the jack and diode). If you publish them here, folks will be able to tell you if it looks right or there's an issue.

[edit: sorry, was writing and didn't see your reply above]

 

[BrainDrain]

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.

 

[BrainDrain]

Sure, status LEDs lighting/not lighting is information, but can also be the result of issues totally unrelated to the signal and it's processing in the circuit (i.e.: a burnt out LED, bad solder on the 3pdt switch, etc). Other than power supply, it's not directly relevant to the main circuit and won't tell you anything about issues in signal processing there--whether it works or doesn't work doesn't affect anything at all. Proof is I've stopped putting LEDs in 90% of my builds because it's my least favorite part of building until I audition the pedal as a keeper. Obviously this doesn't apply to LEDs within an LED/LDR array that are functional in LFOs or what have you.

@BrainDrain if you suspect a problem with current, then you can plug the pedal in, connect one end of your multimeter to a pedal ground, and probe and write down all voltages at the IC and transistor pins (since you've already done the jack and diode). If you publish them here, folks will be able to tell you if it looks right or there's an issue.

[edit: sorry, was writing and didn't see your reply above]

In this case the LED not lighting told me there was some kind of voltage problem after I eliminated the wiring, foot switch and a defective LED. I do agree In most cases it's useless but in this case it helped lead me back to where the voltage was being lost at the broken trace. Either way, thanks for the help. Much appreciated

 

[Giorfida]

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.

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!!