Smoking DEFX Laika Fuzz v2

[Itchy Scratcherson]

    Greetings! My name's Christopher and I'm a diy-pedalaholic: >125 pedal circuits assembled in the one year since my addiction started. My gateway activity was modding all my electric guitars during the pandemic. Anyway, I know just enough to be dangerous. My soldering skills have grown leaps & bounds. I know music production & engineering well, but not EE. Schematics & spec sheets I can read easily. Mac user since '91! My questions are in the final paragraph below...
    So Laika is one of the several fantastic DEFX pedals I've made, and it'll get boxed eventually. Top-shelf, man. Exceeded my sonic expectations much like the several Cornish clones I've put together. Thing is, I can't hear whether the Drift 3PDT is functioning or not, nor the Scan Pot. Oscillation? What oscillation?
    A few details: I tried a 1n34a which was fine & now NOS Philips OA7. Ge transistors are NOS MP16B's; all 3 w/gains only in the 60's. Tweaked the 25K trimmers to give me just above 6V on the Collectors (correct?) of Q3 & Q4. Q2's Collector's hi 4's or ~5V, I think. I'll post precise voltages tomorrow.
    All silicon transistors agree with the build doc: 2N3904, 2 x BS170, 2SK30A-Y, and one BS250 [SOT-23]. Proactively reflowed most joints on the whole Laika pcb. btw, DEFX's PCB's are among the best, most robust, imo.
    So, 4 things (1.) neither LED lights up (2.) Diode Reverse toggle doesn't have any audible effect. Does it respond better to certain settings? Is it the spec of the diode being too similar in either direction? (3.)  where to start troubleshooting the Drift & Scan functionality? I'm in the middle of verifying continuities around 'em according to the schematic. (4.) After I randomly tweaked the 50K trimmer to see if/how it effected the Scan, I played a bit & the Scan pot seemed to change the sound just a bit, maybe. WHEN SOMETHING STARTED SMOKING I shut the whole thing down and started typing here. Oy vey. I've posted pics b/c I can't see signs of any burnt component. The small puff of smoke seemed to come from the 50K trimmer, middle Ge transistor, or the Scan pot areas. My sense of smell isn't great so I can't pinpoint that wonderful scent on the pcb.
    Sorry so verbose! Thank You So Much!
~Christopher

[soggybag]

Pull out all of the socketed transistors. Then get your multimeter and start checking.

- start with power is there 9v at the power jack?
- check the base of each transistor. If these are BJTs you probably have about 1.2v
- check the collector of each transistor this should be around 9v
- the MOSFETs should have about 4.5v at the gates.
- emitters, and source will have 0v. Reverse that for PNP types.

Examine the schematic and guess what you expect the voltage to be and if anything is way off. For example, op-amps will have 9v at pin 8 and 0v at pin 1, bias voltages for op-amps will be 4.5v.

Once things stop moving make an audio probe and start testing with that.

I started a page with debugging advice: http://www.super-freq.com/debugging-your-circuit/

[Mark Hammer]

    Greetings! My name's Christopher and I'm a diy-pedalaholic: >125 pedal circuits assembled in the one year since my addiction started. My gateway activity was modding all my electric guitars during the pandemic. Anyway, I know just enough to be dangerous. My soldering skills have grown leaps & bounds. I know music production & engineering well, but not EE. Schematics & spec sheets I can read easily. Mac user since '91! My questions are in the final paragraph below...
    So Laika is one of the several fantastic DEFX pedals I've made, and it'll get boxed eventually. Top-shelf, man. Exceeded my sonic expectations much like the several Cornish clones I've put together. Thing is, I can't hear whether the Drift 3PDT is functioning or not, nor the Scan Pot. Oscillation? What oscillation?
    A few details: I tried a 1n34a which was fine & now NOS Philips OA7. Ge transistors are NOS MP16B's; all 3 w/gains only in the 60's. Tweaked the 25K trimmers to give me just above 6V on the Collectors (correct?) of Q3 & Q4. Q2's Collector's hi 4's or ~5V, I think. I'll post precise voltages tomorrow.
    All silicon transistors agree with the build doc: 2N3904, 2 x BS170, 2SK30A-Y, and one BS250 [SOT-23]. Proactively reflowed most joints on the whole Laika pcb. btw, DEFX's PCB's are among the best, most robust, imo.
    So, 4 things (1.) neither LED lights up (2.) Diode Reverse toggle doesn't have any audible effect. Does it respond better to certain settings? Is it the spec of the diode being too similar in either direction? (3.)  where to start troubleshooting the Drift & Scan functionality? I'm in the middle of verifying continuities around 'em according to the schematic. (4.) After I randomly tweaked the 50K trimmer to see if/how it effected the Scan, I played a bit & the Scan pot seemed to change the sound just a bit, maybe. WHEN SOMETHING STARTED SMOKING I shut the whole thing down and started typing here. Oy vey. I've posted pics b/c I can't see signs of any burnt component. The small puff of smoke seemed to come from the 50K trimmer, middle Ge transistor, or the Scan pot areas. My sense of smell isn't great so I can't pinpoint that wonderful scent on the pcb.
    Sorry so verbose! Thank You So Much!
~Christopher

So, um, do you have any 10k resistors? 

[duck_arse]

also welcome to the forum. but, you'd be posting the link to the build docs, wouldn't you? y'no, just so's we know what we are looking at.

[Itchy Scratcherson]

BUILD DOCS should be here: https://drive.google.com/file/d/1t9UkjtPVxwSyIMK1RBP7tvHhX9SKaRui/view
Here are my voltages from t'day (see JPG)

[Itchy Scratcherson]

Yellow highlights on my voltage chart indicate the voltage is 0 when bypassed... with my test box feeding 9.14 Volts to the build, I checked bypassed V against "pcb engaged/ON" voltages for all, and everything's getting the same power in either state except the BS170's (Q6 & Q7) and D1 (4148).

[Itchy Scratcherson]

So, 1 step forward and 2 steps back: I think my SK30A (actually 2SK30ATM-Y) has reverse pins from the PCB's etching... so I did flip it (maybe it doesn't matter?). Should've tested the circuit but instead decided to increase Voltage to the Scan pot in case that's what was needed to hear any effect from it. As I up'd the 50K trimmer, I saw the correlating WHITE SMOKE. I think I burned out the Xformer b/c it doesn't measure any voltages now. Ugh. Can anyone hip me to how to verify this transformer? I think only pins 1 & 3 are relevant.
In hindsight maybe I should fix the non-functioning LEDs before the other issues. Replacement transformers arrive Monday.
Thanks Everyone for your sharing insights!

[Ben N]

Very involved, as the Spaceman stuff is wont to be. You might want to give a shout out to Dino/ digi2t of Dead End FX himself, as he is an honored member of this forum and does haunt these precincts from time to time.

[Itchy Scratcherson]

also welcome to the forum. but, you'd be posting the link to the build docs, wouldn't you? y'no, just so's we know what we are looking at.

fwiw, My purple Laika V2 pcb's actual layout seems to be one more evolution/iteration beyond the DEFX posted build docs. Now that the build is all populated, reverse-mapping the location of a couple of the components is frustrating. I should've marked 'em down before soldering. digi2t?

[duck_arse]

two things. your linked build docs are not for your board revision.

and - on the first page of the correct version docs is a note about fitting a link to the board to correct the layout, which I can't see on your build.

[Itchy Scratcherson]

Did I mention I know just enough to be dangerous? Good grief. My assumption when I purchased the pcb recently was that if there are two versions' build docs posted, then I must be getting the latest pcb. So, my bad. Details, details...
@#$&*! "V2" is not on the purple pcb... and further, "2017" is. A fundamental mistake on my part for not seeing what's right in front of me.
Anyhow, forging ahead:  I easily salvaged another transformer from another project, so I'll be back here soon. THANK YOU!

[digi2t]

There are two versions, because we missed a trace in the filter switch section the first time around. The first run release requires that a jumper be added to correct the error. Otherwise, the two versions are identical.

TRIM3 is a mod on our part. The originals used a fixed 22K resistor here, but when I was testing on the breadboard, I found that using a trimmer here lent some additional tweaking room to play around with the reference voltage being sent to the gate of the Drift control JFET (2SK30), as well as C16 on the audio output. (BTW... JFET source and drain are interchangeable, and the 2SK30 being a center pin gate, it shouldn't matter which way you put it in)

Anyway, like I said, tweaking the trimmer adds some additional sound variation within the Drift mode. BUT... if you look at the instructions, it states that the trimmer should be set to 22K first. This places it at original resistance value.

Second, this trimmer is part of a voltage divider arrangement, which is also influenced by the Scan pot. Since the original used a fixed value (22K) resistor as a limiter on the positive side, the Scan pot (100K) controls resistance to ground, and ultimately what voltage is output.

As such, one needs to be reeeeeeaaaaaaallllly careful when adjusting this trimmer. In the case where the Scan pot goes to zero (0 ohms to ground), and if the trimmer is set with too low resistance to 9v, you effectively create a dead short. From the sounds of it, this is probably what happened to your build. You make have gone too far with the trimmer, and shorted the power side of the circuit. This probably roasted the trimmer, and probably the BS250 as well (no LED's lighting up = no power). Check C4 (100u) power cap as well for short to ground, just in case.

You let out the magic smoke. Welcome to the club.

As for the transformer, that's in the audio line, acting as a pickup simulator, so I would be surprised if that is toast... but hey... magic smoke is.... magical.

First things first, I would replace the trimmer (TRIM3). Ensure to set it to 22K (between pins 1 or 2, and 3), or for quick troubleshooting, simply use a 22K resistor between the first and third pads. Set the Scan pot to the center position as well, just for some added cushion.

Next, test the BS250. Apply 9v to the board, check if it's getting across Q1. If yes, good. If not, replace.

Next, adjust TRIM1 and 2 to get the transistor voltages close to what's in the build doc. IIRC, the two trimmers are somewhat interactive, so some back-and-forthing might be necessary. After that...

Put the Drift section aside for now, and test the audio. Are you getting sound out of it? Yes, good. No, get out the audio probe and start tracing. If you did indeed smoke the transformer (or anything else along the audio way), you'll find it soon enough.

Start with that, and report back. I'm not going to get into the Drift section now. Until you get the head right, there's no point worrying about the hoof or tail.

Like I said, first run and v2 boards are identical, except for a missing trace in the filter section on the first run board. That should not have any influence on the issue at hand. "Details details"? Isn't that where the Devil lives?

For our part, we should have perhaps been a bit more intensive where our instructions regarding TRIM3 are concerned. Then again, we've not had an issue come up with it to date. I'll go back and fix that. Probably a limiting resistor between 9v and the trimmer might be a "good thing" for v3. Details. Pleased to meet you. Hope you guessed my name.

[duck_arse]

Otherwise, the two versions are identical.

Sir, no sir. the entire top third of the two versions are totally different for parts placements/orientations. pleased to meet your details, and raise you some observations.

having just watched your demo for this pedal, I can't see me not building a one. verry amusing.

BUT... if you look at the instructions, it states ............

Itchy - I knew you were going to cop it if Dino had to come and tell you things.

[Itchy Scratcherson]

I appreciate your explanations, Dino, so much. Invaluable to me. Couldn't ask for more! Certainly the BS250 isn't passing on any power. My 2 LEDs failed to light from the first time I powered up the circuit. Working on everything now! more soon...
~Christopher

[digi2t]

Otherwise, the two versions are identical.

Sir, no sir. the entire top third of the two versions are totally different for parts placements/orientations. pleased to meet your details, and raise you some observations.

OK OK OK... I was talking about the circuits, but yassir, the board layouts are different. I over simplified. For troubleshooting purposes, the duckster is on the money... use the schemo that belongs to your board.

[Itchy Scratcherson]

OK, I'm back. After assembling a new microscopic BS250 & soldering it directly to the Laika PCB I now have audio! The Ge transistors' Voltages are <> what they were. Pretty sure, as before, the Diode Reverse & the Drift switches don't seem to have audible effect at present, but then again, I didn't touch the Scan pot, even tho I replaced it's 50k trimmer3 & set it to precisely 22k. I'll triple-check all grounds & VREFs are fine.
So, the Drift LED (D5) now lights as expected (replaced after testing NG), but the bypass LED (D2) still does not. It flashed while pressing the bypass 3PDT but only the first few tries/clicks. But, touching pins 1-3 on the Xfrmr w/ the DMM made the LED light up while contact was maintained... but only for the first minute of poking around. Maybe this indicates a grounding issue or not enough voltage is being sent to the LED? I'll double-check it's CLR.
Where to from here? I'll try swapping-out the 3904 &/or the BS170's to get the LED working. Could it be a bogus 3PDT even tho it seems to have good continuity whether it's engaged or disengaged?
   ~Christopher

[Ben N]

... the duckster is on the money...

[digi2t]

So, the Drift LED D5 now lights as expected, but the bypass LED D2 still does not. It flashed while pressing the bypass 3PDT but only the first few tries/clicks. Then when DMM'ing, I checked pins 1-3 on the Xfrmr & the LED stayed solid while contact was maintained. More probing around the Xfrmr and couldn't get the LED to do that anymore.
Where to from here? Troubleshoot the bypass LED first? Maybe I'll try swapping-out the 3904 &/or the BS170's to get the LED working? Grounding issue? Could it be a bogus 3PDT even tho it seems to have good continuity whether it's engaged or disengaged?
   ~Christopher

So, it sounds like (part?) of the issue revolves around the Millennium bypass (Q5/Q6). That's what controls the bypass LED. The Millennium bypass also controls Q7, which is responsible for switching the Drift side Q8 on/off.

If the Millennium bypass isn't working properly, then the Drift won't work, even if your Drift switch/LED is on. Q7 acts as an inverse switch for Q8 to ensure that any noise generated by the Drift circuitry when on gets squelched in bypass. Simply put; if your Mill bypass isn't working properly, then Q7 will not allow Q8 to turn on.

Not quite sure why you keep going back to the transformer. Like I said before, it's used as a pickup simulator, and has no bearing on the power or bypass.
Recommended (mandatory really) reading on pickup simulators; http://www.muzique.com/lab/pickups.htm
If anything, by bridging to the transformer with your DMM probes, you're maybe swinging the current enough to get the LED to light up, but, the issue is still somewhere in the Mill bypass. Maybe accumulated capacitance is giving you a few lights the first few tests, and then nothing? Maybe someone with a deeper understanding can chirp in on that on. Above my pay grade.

Recommended (mandatory really) reading on Millennium bypass; http://www.geofex.com/article_folders/millenium/millen.htm
Just keep in mind that the "low leakage diode" indicated in the paper is the 3904. This should help you sort out your issue.

Start by getting your bypass LED working properly. Then, if your Drift still isn't working, move over to the Q7 and Q8 landscape.

[Itchy Scratcherson]

Thanks, Dino. Read your latest post a few times & read the Millennium BP article twice. Working with my DMM now...

[Itchy Scratcherson]

...learning is taking place...