Troubleshooting Dead End FX Charonium/Last Gasp Misty Caves Reverb

[mdcmdcmdc]

Hi folks,

I finished up my first Dead End FX PCB project yesterday and it's giving me a bit of trouble, so I'm hoping the hive mind here can help me sort it out.

The build documents, including schematics, are here:
https://drive.google.com/file/d/1Q3IoVusmR10JOCUQlSS9JIMDiEl62xII/view

The pedal passes signal when engaged but neither LED is working.
Signal is distorted and the reverb effect is pretty hard to hear, though the modulation seems to be working ok.

Generally, the board went together fine but I made two mistakes (that I know of): 1) I initially put the LEDs in backwards and had to pull/replace. The pads looked ok but you never know...; 2) I installed one of the 4558s upside down and powered the pedal up a few times before I noticed it. I tossed that particular IC but again, maybe it damaged something down the line?

Aside from those gaffes, no parts substitutions were made. EDIT: after posting this I remembered that I *did* actually sub one part. The BOM calls for a 460r resistor, I sub'd a 470r iirc. I'll pull that out and put a couple things in series to get 460 in that spot.



You can see a dark spot on the top of one of the electrolytic caps—I didn't notice that when I was soldering the board together. The silver looks cracked, but it's not bulging or leaking or anything—not sure if it's just cosmetic?

I haven't gotten far enough along to start adjusting the trimmer or anything like that.

The schematic is more complicated than I'm confident tracing on my own, so any suggestions on where to start in terms of checking IC pin voltages, or how to start figuring out where things are going sideways on the board would be really appreciated.

Thanks greatly (in advance) for the help!

[mdcmdcmdc]

Wow, apologies for the stray cat hairs on the board. I live surrounded by fur.

[ElectricDruid]

So neither D3 nor D4 light up, is that right?

D3 suggests that your 3PDT switch wiring isn't right. That is a lot of all-the-same-looking white wires to mix up down in that corner, after all. That might explain why sound isn't going through the pedal. It *might* be working fine, but wired wrong.

D4 suggests that the LFO isn't running. We don't know why that is at the moment. We might need to see the voltages on the chips to be able to work that one out.

I wouldn't worry about putting a 4558 in backwards. It almost certainly won't have damaged anything else.

[iainpunk]

welcome to the forum, i suggest you lookt at this link:

debugging guide

cheers, Iain

[mdcmdcmdc]

Correct - neither D3 nor D4 are lighting up.

I've not built a DFX project before, so their approach to switch wiring was new to me:



I'm

Here are the IC and Q voltages:

• Source measures 9.32v
  Numbering follows PCB
  First reading w pots fully CW, second w pots fully CCW
  Only one value means no change when pots were moved
  On readings marked "unstable," the voltage given is approximately in the middle of the swing

IC1
1 - 0.00 / 0.00
2 - 2.66 / 3.40 (unstable)
3 - 2.31 / 2.31
4 - 5.33 / 6.50 (unstable)
5 - 5.71 / 7.00 (unstable)
6 - 2.68 / 3.40 (unstable)
7 - 3.13 / 3.30 (unstable)
8 - 3.13 / 3.40 (unstable)

IC2
1 - 4.28
2 - 4.28
3 - 2.13
4 - 0.00
5 - 4.20
6 - 4.26
7 - 4.26
8 - 9.32

IC3
1 - 5.71 / 7.00 (unstable)
2 - 2.66 / 3.40 (unstable)
3 - 0.00 / 0.00
4 - 2.68 / 3.40 (unstable)
5 - 2.51 / 3.30 (unstable)
6 - 2.75 / 3.60 (unstable)
7 - 2.76 / 3.10 (unstable)
8 - 5.33 / 6.50 (unstable)

IC4
1 - 3.10
2 - 3.10
3 - 1.83
4 - 0.00
5 - 4.24
6 - 4.26
7 - 4.26
8 - 9.32

IC5
1 - 3.00 (unstable) / 4.00 (unstable)
2 - 2.84 / 3.50 (unstable)
3 - 2.70 (unstable) / 3.50 (unstable)
4 - 0.00 / 0.00
5 - 2.84 / 3.50 (unstable)
6 - 2.86 / 3.50 (unstable)
7 - 2.60 (unstable) / 3.40 (unstable)
8 - 5.71 / 7.00 (unstable)

Q1
E - 3.20
C - 9.32
B - 3.12

Q2
E - 2.32
C - 9.32
B - 1.70


...and just in case it's helpful here are D3/D4:
D3
A - 0.00
K - 9.28

D4
A - 0.00
K - 1.50 (unstable) / 2.00 (unstable, bigger swing)

I'm assuming K = square pad here.

[ElectricDruid]

OK, thanks. That helps.

IC1 is the BBD, and there's only three pins that have DC on them: pin 1, 4, and 5. The outputs have DC bias, but only those three should be steady.
You say that pins 4 and 5 are unstable, which doesn't sound right. Those are the power supply to the chip, so they should be fixed.

IC2 is a dual op-amp, the input buffer and first filter. That looks fine. Pin 3 is low, but that looks like meter loading to me, not an actual fault. Note that it's almost exactly half what it should be (4.28V like the others).

IC3 is the clock generator chip. Again, only pins 1, 3 and 8 can be expected to show a steady voltage. Yours aren't doing that, which isn't good. At the least the ground connections are ok!

IC4 is more op-amps. The first one (pins 1,2,3) doesn't look right, but the second one (pins 5,6,7) is ok. That R34/100K resistor wrapped around the IC4_A voltage follower stage is confusing me. I haven't seen anything like that before.

IC5 is the LFO. Again, it's attached to that +V1 supply which seems to be wobbling about all over the place. That's not right. The rest of the pins look terrible too, but if the power is unstable, that's probably to be expected!

I think getting that power supply stable is most important, since until that's fixed, the clock, the BBD, and the LFO are all up in the air. My first question is "what's causing the wobbling about?". Since clocks and LFOs both oscillate, I would try removing first IC5 and then testing the power pins on the BBD again. If that doesn't fix it, remove IC3 (the clock chip) too, and then see if it's ok.

If either of those fixes it, you need to be hunting for mistakes (wrong component, wrong value, wrong orientation), solder bridges, or bad joints in those two areas (LFO and clock/BBD).

Good luck!

[mdcmdcmdc]

Thanks - that's really helpful, I'll give that a try.

[mdcmdcmdc]

IC1 readings w IC5 pulled (CW / CCW):
1 - 0.00 / 0.00 
2 - 3.03 / 4.09 
3 - 2.32 / 2.32 
4 - 6.05 / 7.72 
5 - 6.48 / 8.26 
6 - 3.05 / 4.09 
7 - 3.24 / 4.29 
8 - 3.25 / 4.29

I swapped IC5 out for a different 4558 and the readings were identical to what they were previously - lots of voltage swing with the knobs dimed.

So that would indicate the issue is somewhere around the LFO?

[PRR]

I questioned chips going different ways, but for whatever reason, that's what the doc shows.

I do not like the looks of some solder joints. (Agree that more than 7 wires same color is another begging for mistakes item.)

[mdcmdcmdc]

Spent some time trying to sort this out today and sadly no improvement. Ran the power along the outside edge of the board in case that was causing some interference, re-flowed the solder connections to the switch. No sign of solder bridges, but I'm pretty sure the two LED pads are cooked as they're still not coming on when the unit it powered up.

I'd be wildly grateful if anyone has any ideas about what might be causing the voltage swing, but failing that I may just put it aside until the board is back in stock and give it another go with a clean slate.

[ElectricDruid]

I swapped IC5 out for a different 4558 and the readings were identical to what they were previously - lots of voltage swing with the knobs dimed.

So that would indicate the issue is somewhere around the LFO?

Not unless you tried without the clock chip too.

I'm guessing that one of either the LFO (IC5) or the clock chip (IC3) is the source of the variation you seem to be seeing all over the place. That's not necessarily true, of course. A flat battery in your multimeter can also cause wild readings. If there's a fault somewhere, other bits of the circuit could be oscillating despite not being designed to do that.

But let's go with the theory for a second. What happens to the voltage on pin1 of the IC3 socket with both IC3 and IC5 pulled? Is it a stable voltage? What is it?

If that doesn't work, pull *all* the ICs from their sockets, and verify that you have a stable power supply. You should have steady 9V across pins 4 and 8 on the dual op-amps. There'll be a bit less on IC5, because it's run off the filtered +V1 supply.

If it's still wobbling all over the place with all those chips removed, you either have a very dodgy power supply, have a broken multimeter, or have superpowers you haven't realised yet.

[mdcmdcmdc]

Apologies if that earlier post wasn't clear - with IC5 pulled the voltages stabilize.

I swapped in a new 4558 after taking those measurements to see if it was a faulty chip causing the issues, but the readings immediately went back to the original values. So they're consistently inconsistent I guess?

with IC5 pulled I get a stable 8.3v on pin1 of IC3
with IC3 and IC5 pulled I get a stable 9.12v on the pin1 socket of IC3

with every IC pulled I get
9.34v at the source
9.34v btw pins 4+8 on IC2 and IC4
9.12v btw pins 4+8 on IC5

Which seems to go along with what I *should* be seeing if I'm not mistaken?

[ElectricDruid]

Apologies if that earlier post wasn't clear - with IC5 pulled the voltages stabilize.

Ok, that's good. I hadn't understood that. That's definitely progress.

I swapped in a new 4558 after taking those measurements to see if it was a faulty chip causing the issues, but the readings immediately went back to the original values. So they're consistently inconsistent I guess?

That's a good thought. If it does it with whichever chip, then it's not the chip and must be something on the board.

with IC5 pulled I get a stable 8.3v on pin1 of IC3
with IC3 and IC5 pulled I get a stable 9.12v on the pin1 socket of IC3

with every IC pulled I get
9.34v at the source
9.34v btw pins 4+8 on IC2 and IC4
9.12v btw pins 4+8 on IC5

Which seems to go along with what I *should* be seeing if I'm not mistaken?

Yes. That looks good.

So I agree with you - it does look like there must be something funny going on with the parts around the LFO.

Check those 10K/100K resistors. It's a bit hard to tell from the photo, but it's easy to mix those up. Check for any shorts or bad joints around those LFO components.

[mdcmdcmdc]

Looks like the six resistors and two caps around the LFO IC are correct; I checked for solder bridges and even re-flowed the solder connections when I had it pulled apart last night so I'm semi-confident that the parts are in the right place and hopefully connected properly.

Could a faulty or incorrect optocoupler be causing these issues? I ordered the spec'd part from smallbear (VTL5C3) but I have no idea how to check that part independently.

Similarly, I assumed that the LEDs D3 and D4 were cathode to square pad as that's how the other diodes on the board are indicated, but the PCB also uses square pads as positive for the electrolytics. D3 and D4 don't have polarity marked—I reached out to dead end for clarification on it. Could a blown or backwards indicator LED in that area be causing power supply issues?

[mdcmdcmdc]

Heard back from dead end - the square pad is actually the anode for the two LEDs so those are in backwards. I guess this explains why they never worked! I'm doubtful that the pads will survive another round of solder sucking and heat but who knows...

[mdcmdcmdc]

Bumping this thread to say that this particular build has been flummoxing to me like no other I've attempted. I don't think there's anything particularly complex about it, but for some reason it's showing me no love.

I have the modulation section up and working fine after much frustration. But per the build docs, I'm unable to get the circuit to self-oscillate in order to dial in the the internal trimmer. I thought it might be a bad trimpot so I pulled that and replaced it with a new one; no change. I also went ahead and swapped out all of the ICs and transistors to see if that had any effect. No dice.

The blend works fine, the modulation works fine, there's plenty of output level, I just can't get anything past the slightest bit of delay out of the circuit with the "TIME" control dimed.

I'm curious if using a different, higher value trimpot in place of the 10K will help goose it a bit? Would changing the value of R29 or C18 have much effect?

Build doc and schematic are here:
https://drive.google.com/file/d/1Q3IoVusmR10JOCUQlSS9JIMDiEl62xII/view

[mdcmdcmdc]

Double checked the resistor and cap values around the V3102 chip as well as around the immediate surroundings (everything in the vicinity of the 10K trimmer and the 3102/3207) - they all look correct; swapped out every IC and transistor on the board (including the 3102/3207); sadly no improvement. I can't for the life of me figure out what's going on with this thing.

If anyone has familiarity with these kinds of BBD circuits and could point to potential trouble spots in the schematic that would be a huge help; eg, if the circuit isn't able to feedback on itself and generate the delay/reverb effect, is that a symptom of anything in particular?

I've cut the schematic out of the build doc pdf:


Higher res:
https://imgur.com/5X2RKDa

[dirtyuncleleo]

im in the middle of my own build of the charonium so i hear you about those LED pads. this may be a very stupid suggestion BUT... did you wire up the stereo switched jack, or do you have those wires floating freely? i didn't have my jack when i built it at first and didn't bother soldering in the wires, and nothing was happening, so i had to put in some wire and connect them to each other (tip/tip, etc) so the signal was complete.

apologies if you have it in... i couldn't tell from the image.

[mdcmdcmdc]

I did wire up the cliff jacks, double checked the connections and it seems to be working correctly (or at least not NOT working—I haven't tried it w an expression pedal).

A couple of folks on the dirtbox layouts blog who built the vero layout of this seem to have run into the same issue: modulation works fine, but it won't resonate or reverberate. I'm thinking it might be the BBD chips? Maybe the coolaudio ones won't work in this circuit for some reason?

FWIW, here are my voltage measurements from when I last took a stab at troubleshooting:

PSU reads 9.33V
All knobs dimed

9.33 at source

IC1
1 - 0.00
2 - 3.35-3.50 (unstable)
3 - 3.59
4 - 3.35-6.64 (unstable)
5 - 6.80-7.15 (unstable)
6 - 3.37-3.50 (unstable)
7 - 4.99-5.04 (unstable)
8 - 4.99-5.04

IC2
1 - 6.35
2 - 6.35
3 - 3.16
4 - 0.00
5 - 6.23
6 - 6.34
7 - 6.32
8 - 9.32

IC3
1 - 6.80-7.15 (unstable)
2 - 3.35-3.52 (unstable)
3 - 0.00
4 - 3.35-3.52 (unstable)
5 - 3.20-3.35 (unstable)
6 - 3.49-3.62 (unstable)
7 - 3.10-3.24 (unstable)
8 - 6.35-6.65 (unstable)

IC4   
1 - 4.48
2 - 4.48
3 - 2.66
4 - 0.00
5 - 6.29
6 - 6.32
7 - 6.32
8 - 9.33

IC5
1 - 1.40-6.10 (unstable)
2 - 3.35-3.52 (unstable)
3 - 2.47-4.20 (unstable)
4 - 0.00
5 - 3.35-3.52 (unstable)
6 - 3.46-3.57 (unstable)
7 - 3.46-3.57 (unstable)
8 - 6.80-7.10 (unstable)


Q1
E - 5.03
C - 9.33
B - 4.62

Q2
E - 3.61
C - 9.33
B - 2.46

[Ry]

I will agree that mine works just fine otherwise, but won't  resonate no matter how the trimmers are set.  I didn't find the pedal  terribly interesting, though, so I moved on in builds.  I will revisit my build to see if I can figure it out now that it seems like multiple people have the same issue.