Lack of gain - Yet Another Klone Troubleshoot (YAKT for short?)

[eatswires]

I'm building the Ceriatone Centura
Docs and schematics: https://ceriatone.com/wp-content/uploads/2017/07/Centura-Instruction-010717-Doc.pdf

Standard circuit, no mods, no substitutions. Very careful about using the right components

I've built a handful of pedals before: fuzzes, distortions, drives, noise gates, and I'm usually able to diagnose issues OK. Not this one.

I have scoured the boards to the best of my ability and not found anything that solves my issue. This is closest and it's unresolved: https://www.diystompboxes.com/smfforum/index.php?topic=108099.msg984137#msg984137

Pretty sure the pot is fine from testing it.

Tone and volume controls seem to work great, very similar to other klones I have, but the gain is totally wrong. It actually gets quieter and duller as the gain blend is increased and seems most muffled at 12 o'clock, gaining a tiny bit of volume back after that but barely any clipping at all. Not too sure how to troubleshoot the diodes, my DMM doesn't seem to be helpful with testing methods I've looked up.

I did blow up multiple LEDs testing the circuit before figuring out it was a bad choice of DC jack that was shorting against the enclosure. Doesn't bode well for what else I may have fried...

I also managed to create a solder connection between R21 and R22, the solder points there are very close and I couldn't remove it for fear of ripping up the trace. However it looks like that connection is the existing circuit path between those points anyway and not actually changing anything?

IC readouts. 2 and 3 are way off.

IC1 - TL072
1. 4.67
2. 4.63
3. 1.24
4. 0
5. 4.60
6. 4.67
7. 4.67
8. 9.38

IC2 - TL072
1. 4.71
2. 0.04
3. 0
4. 0.65
5. 0
6. 0.05
7. 7.23
8. 8.05

IC3 - ICL7660CPAZ

1. 9.38
2. 0.23 (drifts)
3. 0
4. 0.12
5. 0.77
6. 0.16
7. 0.03
8. 9.38

DC protection diode: "-608" on my crappy DMM in diode mode

Germaniums are 1N34A and drop from 500 and 800 (50v and 80v?) respectively

Pics attached

[drdn0]

You don't appear to have a voltage multiplier/inverter working - there's no negative rail, nor doubled rail.

Start there

[antonis]

Hi & Welcome..

I'd check for IC3 bent legs..
(pin 8 connection to socket looks suspect..)

[duck_arse]

also welcome.

might I say, that is not a viable way to connect your pots. the board at an angle puts mechanical stress on the pot lugs, and the pot lugs put mechanical stress on the PCB pads. which will lift, and cause odd non-connection problems. every time you clunk the bypass switch, the board will twang from inerta, and the stresses will produce dry, crystaline solder joints at the pot lugs. will.

you are better off soldering resistor leg cut-off to the pot lugs, and then soldering those leads to the board, such that the board can be firmly mounted to the case, spaced FROM the case, so as to avoid any tracks shorting to the case. the other thing is black wire. use some colours, makes it easier for outsiders to see where your pots connect.

[eatswires]

Thank you all for taking a look here it's a great help!

You don't appear to have a voltage multiplier/inverter working - there's no negative rail, nor doubled rail.

Thanks, yes very true. I can see that the ICL7660SCPAZ is not converting voltages in any of the ways it should be. I just can't tell whether it's the IC itself or not and I'm not sure how to test the functionality of the IC. May grab another to see if it's defective. Wondering if it's more a case of what the IC is being sent.

that is not a viable way to connect your pots

Thank you! You are certainly not wrong. I realized this once it came to install and I'm likely going to redo with some wire or lead jumper connections.

I'd check for IC3 bent legs..
(pin 8 connection to socket looks suspect..)

Thank you, good eye! There's a tiny bend to that leg, I took it out to check and it's barely visible, mostly the light in the photo. I tested and there's great continuity from all pins into the socket solder points on the other side of the board.

When I went back to test some more I blew yet another LED. I double checked and the 3.9k LED resistor is definitely 3.9k and working. Wondering if I'm shorting something against the enclosure, maybe just the LED leads. Going to remove the board from it for now and likely rework the pots while I continue to figure this out.

Thanks again for the input, it's a massive help and motivation!

[tootsMcgee]

Some of the wires sticking through the holes look a little long.

A good troubleshooting strategy is to make sure everything is neatly clipped and also remove flux with your solvent of choice (I use 91% isopropyl and a toothbrush and sometimes a Q-tip; do several passes, one to loosen the crap and another to rinse it away). Flux will hide shorts. Plus it makes it nicer to look at

A very dumb question on my part but are you sure the polarity on the power jack is correct? ... and that it's a 9V center negative power supply?

[eatswires]

Some of the wires sticking through the holes look a little long.

Wow yeah can't believe I forgot to trim those! I've cleaned and been over the circuit with a magnifier and don't find any shorts that I can tell. No change.

A very dumb question on my part but are you sure the polarity on the power jack is correct? ... and that it's a 9V center negative power supply?

Definitely worth asking the dumb questions haha. It's the same 1spot 9v center negative that I use with all my built and bought pedals. The DC jack is the standard 2.1mm that I use in all builds, wired the same way as usual. The positive lug is connected to W1 on the PCB, the negative, riveted L shaped lug is connected to W6. Skipped the battery clip to the switched lug bc I don't use batteries.

The jack wired the other way round the circuit doesn't work at all. +9.2v is coming into the circuit.

Also it seems like some of the voltage conversion from IC3 must be happening because a lot of the IC1 and IC2 voltages that should be halved to 4.6 are reading as that.

I'm still pretty stumped!

[ElectricDruid]

The jack wired the other way round the circuit doesn't work at all. +9.2v is coming into the circuit.

Also it seems like some of the voltage conversion from IC3 must be happening because a lot of the IC1 and IC2 voltages that should be halved to 4.6 are reading as that.

+9V coming in is a good start!

The "halved 9V" VB supply is done passively by R29/R30 and C18 and doesn't involve any IC, so that's why that's working despite everything else being wrong. Unfortunately it doesn't prove anything about IC3 working or not. Incidentally, the first two op-amps IC1.1 and IC1.2 are powered off the 9V supply and that VB voltage for bias, so they should be ok and you'll get sound that far at least.

But drdn0 is right - you absolutely need to get the 18V and the -9V power working before you can do much other testing. Check for shorts around IC3. Check that all the diodes around IC3 are the correct way around (D4-D6). Check that the electrolytic caps are the right way around (C19-C22). Oh, and check you put the right chip in the right socket, because stupid stuff like that happens all the time!

PS: The others have already said it, but Welcome!

[eatswires]

The "halved 9V" VB supply is done passively by R29/R30 and C18 and doesn't involve any IC, so that's why that's working despite everything else being wrong. Unfortunately it doesn't prove anything about IC3 working or not. Incidentally, the first two op-amps IC1.1 and IC1.2 are powered off the 9V supply and that VB voltage for bias, so they should be ok and you'll get sound that far at least.

Ah I see!

Well, I checked everything suggested and more and I found an issue with the tantalum cap. It was soldered in fine but touching or gently pushing it suddenly filled out the signal so the gain pot no longer reduced the signal and it was much closer to how it should sound. Still no clipping as such and still the same voltages. But closer.

So I swapped out the tantalum cap thinking it must be bad. Made extra sure the + markers are lined up with the PCB.

Thing is I had a hell of a time getting solder out of one of the holes and I think I must have cooked something, bc now the thing is essentially dead. Bypass works, engaged there is a signal but you have to literally dime an amp to hear anything at all. Voltages about the same.

Time for a break I think...

[eatswires]

Well, I got there in the end. Picked it up back up and swapped out some caps, reflowed a lot of joints and finally everything is working as it should. Also redid the pots in a more sane way. Thanks again for all the helpful pointers, all.