Help - Klon clone debugging

[duck_arse]

a dual wipe.

well, while we are loading-up the OP with things to do, I say "pull IC2 and IC3, see if IC1 then comes good." anyone else?

+1 all points to gain pot.

[EBK]

a dual wipe.

well, while we are loading-up the OP with things to do, I say "pull IC2 and IC3, see if IC1 then comes good." anyone else?

+1 all points to gain pot.

Well, IC2 has to come out in order to replace it anyway, so, sure, let's be a bit more methodical .
I like your plan.

OP did replace the gain pot as a debugging step, which pushes me more toward bad IC2 (or bad socket since we now know there is precedent).

[bean]

Gonna take a stab here - are you using Tayda parts in this build?

[Dangaridoo]

Sorry for the delay - life got in the way for a few days.

Edit: Just modifying this message to put Replace IC2 first. 


Could you verify the color bands on R11 and R17 for me?
R17 should be Red, Purple, Black, Red, (Brown), but I can't make out the first two due to that shadow.  Likewise, R11's first two bands are obscured (should be Brown, Green, Black, Red, (Brown)).

I've been visually double checking your parts and connections.  I'm unable to verify the markings on those two resistors and all the caps that aren't marked on top.  Can't read the markings on IC2 or IC3 either.

Additionally, can we have a peek at the gain pot wiring under that tape?

No worries - Here's a link to better pictures for verification of R11, R17, IC2 and IC3: http://imgur.com/a/Wk84V

With regards to the caps, you'll just have to take my word on it (can't get good pictures) - I've double checked all the caps that aren't marked on top and they read:
C21 - 1uF
C20 - 1uF
C19 - 1uF
C22 - 1uF
C15 - 4.7uF
C17 - 47uF
C18 - 47uF
C6 - D100 394 (seller packaging indicates 390nF)
C8 - 391 (seller packaging indicates 390pF)
C16 - 105 (seller packaging indicates 1uF)
C13 - 821 (seller packaging indicates 820pF)

Can't do the gain pot for a few days yet sorry.

are there any straws left for the grabbing? the Vb should not change at all, any pot setting, certainly not at the R29//R30 point.

can you lift the "GAINA" pot wiper from the Vb, and the "GAINB" pot pins 1 and 3? you should get signal good thu IC1 at least, if that's where the problem is.

I'll try get around to trying the Gain pot in a few days!

Could you do me a favor and measure your bias voltage with the gain at max after it stops passing signal? My theory is that the circuit is pulling the bias to ground with the gain pot at max, for some yet undetermined reason (bad cap in the bias supply maybe).

Pin 1 on IC2 is way too high, should be at the bias voltage (4.5 or so) and pin 7 is way too low, should be at bias voltage.

I recommend replacing IC2 with a new chip, not the old IC1 and see if there's a difference.

BTW, here are my confirmed good voltages. They echo Bean's

Thanks for the comparison voltages!

I measured Vb after it stabilised (after about 15 minutes) - it was sitting at around 4.03v. I measured at R29//R30.

Unfortunately - I'm all out of spare TL072's at this stage... so I can't give IC2 a completely new chip (I'll order some soon, but they won't be here for a few weeks).

Are the IC's socketed? I once came across an internal short in the socket itself (poor molding?). Drove me insane before I found it. It was one of these types of sockets;

Yeah, the IC's are socketed - but I've avoided the type of socket you've indicated (they drive me mad!).

What I used instead: http://www.taydaelectronics.com/connectors-sockets/sockets/dip-sockets/8-pin-dip-ic-socket-machine-tooled.html

I did a continuity check on all the sockets for peace-of-mind, they're fine

a dual wipe.

well, while we are loading-up the OP with things to do, I say "pull IC2 and IC3, see if IC1 then comes good." anyone else?

+1 all points to gain pot.

You got it! I built another audio probe, then proceeded to pull IC2 and IC3. IC1 continued to exhibit the same issues (bad voltages, massive volume loss on pin 7,  etc)

Gonna take a stab here - are you using Tayda parts in this build?

Yes! Is that bad?

Suppliers utilised:
*Tayda provided the majority of parts (all common resistors, most of the caps, sockets, ICs, jacks, knobs, switches)
*Element 14 (http://au.element14.com/ - a proven reliable supplier) provided all of the harder to find parts (uncommon resistors, uncommon caps)
*Random internet sellers - For NOS/difficult-to-acquire diodes only

[EBK]

Gonna take a stab here - are you using Tayda parts in this build?

Yes! Is that bad?

I have no personal experience ordering from Tayda, but I am not sure the name has come up in many non-debugging threads.... 

I don't know much about good part sources in Australia though.  In the U.S., I order pretty much exclusively from Mouser, Smallbear, and Mammoth.  Occasionally, I'll grab something from Amazon if I'm in a hurry or if it isn't specifically pedal-related.

[bean]

Yes! Is that bad?

Suppliers utilised:
*Tayda provided the majority of parts (all common resistors, most of the caps, sockets, ICs, jacks, knobs, switches)
*Element 14 (http://au.element14.com/ - a proven reliable supplier) provided all of the harder to find parts (uncommon resistors, uncommon caps)
*Random internet sellers - For NOS/difficult-to-acquire diodes only

Maybe, maybe not. But, often when I see people struggle with build issues that don't have an obvious cause it comes down to components and Tayda is definitely a frequent offender in this area. Passives are generally okay (resistors, caps and so on though they may be out of spec) but actives are much more suspect. I've even asked folks on the MBP forum to stop buying charge pumps from Tayda b/c they are frequently junk. Not saying that's the cause of your current woes but it is something to keep in mind.

[Dangaridoo]

Well guys, I've good news and bad news.

The good news: The pedal works now!!! Thanks again, I really appreciate all the help from everyone 

The bad news: I'm apparently retarded. C16 was around the wrong way.

Lessons learnt: RTFM.

[EBK]

C16 was around the wrong way.

That was it?  Nothing else wrong?

[duck_arse]

is C16 the only tantalum on the board? if it was that tant, you threw it away and used a new one, yes?

debugging at a distance. it seems to come down to those pesky markings on the parts a lot, recently.

[EBK]

Plus, tantalum is evil.  I swear the first time I heard of tantalum caps was in a foot note saying to never use them.  I never bothered to find out why.   

[Dangaridoo]

C16 was around the wrong way.

That was it?  Nothing else wrong?

Well, I replaced it too, so maybe it was dud? But yeah... Wrong way round.

is C16 the only tantalum on the board? if it was that tant, you threw it away and used a new one, yes?

debugging at a distance. it seems to come down to those pesky markings on the parts a lot, recently.

Replaced yup. Yeah I'm blown away at the mistake honestly - sorry for the waste of time 

[EBK]

Replaced yup. Yeah I'm blown away at the mistake honestly - sorry for the waste of time 

You didn't waste my time. I learned what a backwards tantalum can do.  That little nugget is in my head for future debugs.  I imagine you've learned some things too.  Time well spent.

[duck_arse]

Replaced yup. Yeah I'm blown away at the mistake honestly - sorry for the waste of time 

You didn't waste my time. I learned what a backwards tantalum can do.  That little nugget is in my head for future debugs.  I imagine you've learned some things too.  Time well spent.

+1, many times over. we are writing out a list, just added 'tants - any? direction?', and the next time somebody says "I've ......." we'll hit em with the whole list, THEN start the debug.