Tremolo Issues!

[SirHugo]

Hello again!
I'm having issues with my Pedal PCB woodpecker tremolo (EQD Hummingbird clone)
The pedal is getting power, the foot switch works well, the led comes on and there is sound
Both on and in bypass. The level knob works very well and provides a very nice clean JFET Boost, however there is no tremolo! The depth, rate and LFO switch don't seem to do anything.
My audio probe is in need of some love so I'll have to get back on that, I'm also not sure how to trace the signal b/c the schematic is a bit confusing but here is what I got from the multi meter

Q1 2N5089 0 - 0.18 - 0
Q2 2N2646 1.49 - 1.84 - 0.28
Q3 245457 7.66 - 0.54 - 0

C1 22n 0.18 - 0
C2 4u7 0.55 - 0
C3 1uf 1.55 - 0
C4 100uf 5.23 - 0
C5 4u7 1.50 - 0
C6 2u2 7.66 -  0
C100 9.43 - 0

R1 22k 8.68 - 7.66
R2 47k 0 - 0.18
R3 100k 0 - 0
R4 47k 0 - 0
R5 330k 1.50 - 0.18
R6 39R 0 - 0.28
R7 470R 5.24 - 1.84
R8 27k 4.26 - 1.50
R9 470R 5.24 - 8.70
R10 12k 0 - 0.54
R11 22k 0 - 0
R12 100R 0 - 9.43
R100 4k7 9.68 - 9.68

D1 0 - 9.43

LED 9.68 - 0

DC 0 - 9.68

Level B50k 0 - 0 - 0
Rate B50k 5.34 - 4.55 - 4.56
Depth 250k 0 - 0 - 0

[ElectricDruid]

Ok, so it looks pretty clear your LFO isn't working for whatever reason. That's *probably* everything from Q1 rightwards. It's just possible the LFO could be fine and it's actually the components around the Depth pot at fault (e.g. LFO works, but has zero depth so you never knew!) but that's less likely. If you could detect a varying voltage at either end of R5, that might suggest the LFO was ok and the problem was closer to the depth pot (especially if it reacted to the pots as expected). If not, I'd be looking closely at the LFO.

I'd check that area over, and then double-check it. Then have a cup of tea and a nice sit-down, and then triple-check it

T.

[PRR]

> the schematic is a bit confusing

That cell-phone grab(?) didn't do it any good. A link to the Project Page would be clearer.

The UJT voltages do not look right. The "top pin" of the UJT should want to rise over 7V. The fact that B1 sits a little low of E suggests that B1 is not even connected to the 470r resistor string. (The 0.35V may well be a junction diode passing the super-small current of a DMM.)

[SirHugo]

Here's a non screen grab, I'm at work currently, so I'll have a look at the LFO this afternoon,
I can link the project page but they didn't have much there I had to email for the schematic.
Thanks to you both for your time and analysis!

[SirHugo]

Ok I take that back it has since been updated with project docs!
https://www.pedalpcb.com/docs/Woodpecker.pdf

[Andrekp]

First, this is a prime example of how one of those $20 oscopes from China can be a HUGE help.  Mine saved my bacon, coincidentally, when I was building my Hummingbird clone.  Mine wasn't oscillating either.  I use mine all the time to verify signals being present, LFO's properly O-ing,  etc.

What I ended up doing is breadboarding a simple relaxation oscillator to test out my UJT and get a handle on how it works. What I found is that I had the UJT rotated 180 degrees. I can't remember why I had it that way, but once flipped the LFO popped into its thing.  O scope was helpful in this process. 

[SirHugo]

It's very possible it was the pcb print, they informed me that the print may be incorrect on the PCB when I reached out to them for the schematic, and as I look at the newly minted build docs the illustrated pcb has it orientated differently, I'm going to flip mine and see if that fixes it otherwise I may just have to look in to that $20 gem. Anyway you can post a link for it?

[SirHugo]

Welp no change rotating the UJT there is no difference except that in other positions it changes my depth knob into a backwards volume... hmmm

[SirHugo]

Andrekp is there anyway you can post your hummingbird clones voltages?

[Andrekp]

I cant at the moment, but that LFO is really simple.  Just measure everything you can outward of the UJT and make sure everything is connected in the correct order.  It's only like 4 components, so it should be obvious.  Also look for solder bridges - IME, when working with a verified layout, it's almost always solder bridges that mess things up.

If you think the problem is only your LFO, and it sure sounds like it is, then it should be apparent where the problem is for anything other than a bad UJT.  There is a way to test the UJT with resistance that you should be able to find on-line if it comes to that.

One more tip, I found that mine was ticking a bit.  to fix it, I isolated the ground from the LFO section, AND added a 2K trimmer between the 39R and ground in the LFO.  Adding a bit of extra resistance eliminated the ticking and didn't seem to affect the LFO in any real way. 

I like other here, got the cheap oscope at banggood.com.  The one I got is:
https://www.banggood.com/Original-JYE-Tech-Assembled-DSO-SHELL-DSO150-Digital-Oscilloscope-Module-9V-p-1211151.html?rmmds=search
but there are a few to choose from and options to put it together yourself and save a couple of bucks.

It's nothing special, but it is perfect for finding the presence of signals, LFO's working, etc.  It'd be nice if it was two channel to compare phase, but really, it's a $20 oscope...

EDIT:  Thinking about it further, I'm not sure that voltages on the UJT is a useful measure, since they will ideally be changing all the time ( it's an LFO). As I said the LFO circuit is so simple, it should be trivial to verify it.  If you pull that UJT and resistance test it, then put it back in oriented correctly, it should be obvious if the LFO is oscillating.  If not, start looking again.  There are only a small number of components and outside connections.  It's sounds like the rest of the pedal is working, so it's an LFO issue, which is easy in this one.

[SirHugo]

Thanks for the link man, this is my first trem build can you tell me which componants I should be looking at for the LFO cuicit

[Kipper4]

everything to the right of R5.

[SirHugo]

Ok cool thanks kipper! Ill have a look tonight and report back !

[Andrekp]

Take a look at a simple UJT relaxation oscillator:

https://www.electronics-tutorials.ws/power/unijunction-transistor.html

You'll see that it's basically three resistors, a cap, and the UJT.  In your schematic, it's only slightly more complex.  R6-9, the rate pot, and either C2 or C3.  That's it. 

So measure each leg of the UJT through the resistors to V+ or ground, as appropriate, verify the value of that cap, verify the orientation of the UJT, and there is nothing more to it.  It it doesn't work, then the UJT is bad, or you are somehow shorting the LFO signal out.  If it works, it's obvious, as this is a make-a-statement effect.

The other thing I was saying is that if you run into ticking, isolate the LFO grounds (under the cap and the 39R).  Then add a trimmer between the 39R and that isolated ground.  Turn it up from 0 and the ticking will eventually die out to nothing.  Works in the Hummingbird anyway.   

[SirHugo]

Dose anything jump out to anyone on the voltages I posted? This problem has continued to persist, as far as I can see there dosnt seem to be any solder bridges anywhere, I'm going to try an fix my audio probe to see if that may lend some more clues.

[Andrekp]

If you are getting a nice JFET boost effect, just no trem, then the problem is almost certainly in the LFO not O-ing.

Voltages on the 2646 will vary if it is working correctly - as it will be O-ing.

I'll say it again, as unhelpful as it might seem, the LFO in this thing is about as simple as a circuit can get and it is largely isolated from the rest.  Both of these facts make it very easy to troubleshoot.  It's like 4 or 5 components you need to worry about.

Measure resistance everywhere in the LFO circuit, check your cap is good, then pull the 2646 and resistance check it (see Google for how).  If everything checks out, other than putting your 2646 in backwards, there is nothing to go wrong that shouldn't be obvious.  Really.

Forget about voltages for a second, what are the resistances from each leg of the 2646 to both ground and 9V?

Unless you have an o-scope, you won't really be able to verify much more than that.

If you DO have access, somehow, to an o-scope, pull the 2646 and breadboard a basic relaxation oscillator and get to know how it works.  That will verify conclusively your 2646 and how you put it in and show you how simple this one is. 

Did the maker of your board separate the ground from the LFO from the circuit ground (a good practice) and thus you are missing the LFO ground wire or something?

[SirHugo]

Thanks so much for your very detailed and enlightening response, I apologize for the late retort, I've been overwhelmingly busy and haven't gotten to tinker. Hopefully I'll have a little time to scope it out this week and report back my findings and hopefully have it fixed!
Thanks again to everyone who has responded to my tremolo woes!
-JHK