Obsidius preamp problems

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Vildhjuggah

Member
When I turn on my obsidius preamp the distorted signal doesn't come through (only raw sound and some sizzle). If I flip the toggle switches a million times it will come through, but then I try to flip it to the ones I like (or again at all) it cuts out again. To get it to the setting I like and work at the same time it takes awhile. Also, when I switch the pedal off and back on it normally goes back to no distortion (only raw sound and some sizzle) coming through.
I honestly don't know where to start diagnosing this problem. I'd guess check the switches but this happens no matter which switch I flip so I honestly don't know.
 
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I'm at work right now but I'll check ic3-1 and I'll turn the drive knob like you had mentioned before as well while testing it.
In the earlier testing the back of the pot wasn't touching any of the other solder joints and I actually had the pot bent slightly forward because I looked at the joints under it. But will put something else beneath it before I put it back in the enclose.
 
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Volume noon still drive 0
Ic3-1 has signal
R17 nope
Maxed volume and drive because the volume to test;
Ic3-1 works (not like it should but there is signal)
R17 very little signal with drive maxed but only if the switch near it is up or down, middle position no
 
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You should have signal with the GRUNT sw in all 3 positions. If there is no signal in the center position, then C11 (4.7nF, just above 1N5817), she's-a no good. Since we can't read that capacitor in the photos, can you take a good look at C11 and verify that it is 4.7nF? If it's marked 472 or 4.7n, then we're good. Also, C8, that fat red cap just to the right of the CD4049, is supposed to be 220pF, but it reads 222 which is 2.2nF.
 
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c11 says 472
good call on c8, i had been wondering why that cap was so big anyway and figured i order a weird size one but would still work, turns out i put the wrong one there (checked a lot of the other caps and so far they are correct)
so c8 should be saying 221?
sadly i cant find a cap that value, will have to ask a friend if he has any or order more but who knows if i'll need any other parts
 
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For now, just leave the ATTACK sw in the middle position. Once we get the pedal working, then you can go about replacing C8. 220pF is a pretty common value in pedals, so you might as well buy a few.
 
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I don't nostra, I ordered specifically what I needed (and a few extra of some components like ic's and some of the caps I get extra) when I was building three pedals.
Yeah I'll order some extra when I do. Since mammoth closed I heard about small bear, which is nice cuz the website is better designed in terms of searching parts and their shipping is cheaper.
But I suppose I shouldn't order them until a little more diagnosing.
 
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I'm gonna put the ball back in your court to visually verify all of the parts against the build docs. That includes verifying orientation of polarized parts. It's problematic for the person who built the board to inspect the board because we often see what we expect to see, as opposed to what's actually there. That's one of the reasons we ask for pix.
 
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I believe those two caps that have been the wrong ones are the only wrong parts.

Checked all the caps, (except theres a couple of the box type that i cant see the label) and they're all good besides of course c8.
The green caps are supposed to be nonpolar and have no marks to indicate otherwise like the usual stripe.
The black and gold caps, i have the small gold stripe to the negative (which i know normally its a black stripe but on these nichicon the casing is black with a gold stripe instead so that should be correct).
Diodes/ transistors/ic's are correct in both orientation and item.
No potential shorts anywhere as far as i can tell.
Resistors were easy because i just pull em from their bags and didn't have to do any conversions from uf/nf/pf and stuff so i should have all the resistors right but can go through with a multimeter if you'd like.
I do have some backup ic's of both I believe if its worth a shot swapping them.
 
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I measured all the resistors.
The ones i marked are reading at around half value, and its making me wonder whether they are in parallel or if a capacitor is messing up a reading or something so i figured id check with you first before i swapped them. I double checked by color codes and they are correct.
 

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From left to right,
Top row: R13, R12
Middle row: R8, R7
Bottom row: R102, R101
Measuring large value resistors in-circuit is problematic. If there is a DC path around the resistor, the meter will read low. One thing you can do is measure the resistor one way, wait for the measurement to settle and write down the result. Then reverse the leads, wait for the measurement to settle and write down the result. Whichever reading is the highest will be closest to the truth. May still read low. R7, R8, R12 & R13 have a leakage path thru each other, Q1 and Q2. R101 and R102 have a leakage path thru each other and everything connected to Vcc, Vref and ground.
 
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Alright I'll try that after work and put the highest reading here for each. But yeah besides that everything should be correct, it's just some of the box caps I can't see the label cuz some of them have it on one of the bigger sides instead of the top, but it's right beside another box cap
 
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I think your resistors are fine. Try replacing IC2. CMOS ICs are very sensitive to static electricity damage. Your CD4049s should be stored in an anti-static bag. You should not handle them in a dry (RH <30%) environment. Before you take it out of the bag, ground yourself by touching something grounded, then touch your circuit board, then take the part out of the bag and install it. Where did you buy your CD4049?
 
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Did they come in an anti-static container? I expect they would from Mouser. From Mammoth. who knows? If you don't know how to identify an anti-static container, the good ones are metallized plastic bags. The fair ones are pink or blue and have a slightly greasy feel to them. Real anti-static containers are marked with one or both of these symbols. Scotch tape on the ends of IC tubes is bad. Other than DigiKey and Mouser, all of the online electronics parts vendors I've dealt with either don't know or don't care about ESD protection. So far, I've been lucky, no obviously damaged parts.

ESD symbol.png ESD warning.png
 
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Nope, did some quick probe on the ic points ic1-1, ic2-2. ic2-3 since it wasn't working and still weak signal on ic2-3 with drive and volume all the way up, blend to dist , flipped switches so they arent in middle (because louder when up or down instead). no distortion
flipping switches still isn't getting it to work anymore either
 
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