LectricFx Downtown - SubHarm pot not working

[aleximan]

Hi again.

I checked and reflew some joints on IC13 dis some probing and another round voltage measurements...
While probing  I noticed no sound on pin 2 and 12, also on q4 and q8. Also theE on Q7  and IC11/p7 appear quiet this time... no muff, no sq. wave.

voltage measurements on Q4 and Q8 same as last time but consistant change on IC13 pins since last time (the component probably got busted while handling I suppose?).

1st measurements:  p1 0.00  / p2 9.04  / p3 8.99  / p4 0.00  / p5 9.03   / p6 0.00   / p7 0.00  / p8 0.00  / p9 9.03   / p10 0.00  / p11 0.00  / p12 9.03  / p13 0.00  / p14 9.03 
2nd measurement:  p1 6.99  / p2 7.65  / p3 8.98  / p4 6.99  / p5 9.03   / p6 6.99   / p7 6.99  / p8 6.99   /p9 7.00   / p10 6.99  / p11 6.99  / p12 6.99  / p13 7.59  / p14 9.03

There is a 7v on all positions that had 0.00 before...joints seem all good now...probably a fried IC then?

[Scruffie]

You must have muffled sound (which is actually a sine wave extracted from your input signal) on Q7 collector first, followed by square wave on IC11 pin 7 (follow the schematic) before you get anything on IC13, so you need to find out why that's disappeared again.

But also, your new IC13 measurements, on the second set, you have no ground on pins 4,6, 7, 8, 10... they should all read 0V. Your first set was closer.

[aleximan]

Hello.

I managed to re-flew the joins on IC13, voltages are now the same as in the first measurement, must have been a bad joint somewhere.
I probed all the way from Q7 to IC11 and probably found the cause of the issue...I have the muff on Q7, the signal is fine past R82 and C12 as well as on pins 2 (3.5v) and 3 (3.5v) of IC11.
In the other side voltages on pin 5,6,7 of IC11 are p5 8.95 / p6 8.69 / p7 8.99 ...are such voltages adequate on these pins?...because there is no audible wave as before...just empty signal...does this tell me that probably the LM311N in bad? Reflew all joints on IC11 but no change. 

[Scruffie]

LM311 aren't hugely sensitive and you said it worked before, although I suppose it is possible it died with overheating...

What happens to it if you a) remove IC13 and b) remove IC12?

[aleximan]

Hi Scruffie me again.
I removed temporarily all the sensitive components and did a reflow on some suspicious pin joints of IC13 and IC11...Still no change in Subharm function.
I tried replacing both IC13 and the LM311 with new components from the local electronix shop. Done probing each component after IC12 ...just jacked in my pc with some easy acoustic guitar riffs, 15w amp and go...it resulted that from IC12 forward music could be heard on every component until the region of c30, c31, r85 and finally IC13...Could be a fried cap maybe?
Moving forward I also did the test you suggested...removing IC13 but probing on IC11/p7 no wave...the only audible thing is just a slight whistling noise that my 9v adapter makes. When I removed IC12 changes happened...no clean sound could be heard, just a distorted noise coming in sq. waves on IC13/ p2, p12 and IC/p7...does this give us any clues?

When plugging in my guitar the fuzz is more fuzz-like than the first testing a few weeks ago that sounded more overdrivish with no fuzziness. Bass switch works, tone, blend all works except for the subharm that is not present nor does change while turning the pot.

I'd appreciate any clues. I tried to explain in detail all the testing and results...frustrated. I think something must be wrong just before IC13..should I try to remove or. at least test the caps?

thank you,  Alex

[Scruffie]

Okay, so you wont get octave or anything from IC13 without a square wave coming from IC11.

But, we've determined without IC12, you do get a square wave... does it change in pitch with playing?

IC11 is an oscillator that tracks the pitch of your guitar, IC12 'mutes' this so that it isn't constantly running (oscillating) and you get single notes.

So if without IC12 you are getting a square wave that tracks your input pitch, then the issue must now be around IC12.

[aleximan]

Hmm..playing without the ic12 does not change the pitch. The effect souds like a vibrato. 

[Scruffie]

Where are you probing when you get the 'vibrato'?

By vibrato I assume you mean tremolo? As in a repeating on/off signal?

Pitch might have been the wrong word, does playing change the on/off time?

[aleximan]

The trem effect occurs while playing guitar without the ic12...wasnt probing...just tried it plugged normally. On off time does not change by playing...like a tremolo effect all the time when the pedal engaged.

[Scruffie]

You need to be probing IC11 output (pin 7) but first be sure you definitely still have an input signal to it at pin 3 and make sure sensitivity is full CW while you are testing.

[aleximan]

Hi Scruffie.

Spent a few hours during weekend doin some testing and probing...
I am clueless except for onbe thing...while probing around diode n16 I noticed that there is sound on the + pole but a static whistle on the opposite side...same whistl  can be heard on IC11/p7 and IC12.
Could that be a faulty diode causing the issue? It is right before the IC12 or am I wrong?

ty,

Alex

[aleximan]

My second guess would be a faulty 150p cap on C30 position...one pin has 8.99V and the other 0.00. burned???

[Scruffie]

My second guess would be a faulty 150p cap on C30 position...one pin has 8.99V and the other 0.00. burned???

One pin is the 311 output which is obviously giving 8.99V and one is the ground, so no, that's not faulty.

Audio probing is only really useful if you're tracing your input signal, for example on cathode of D16, when playing, you should get a fuzzy octave up version of your guitar signal.

Did you have input signal on pin 3 of IC11?

I suspect it's probably just a bad solder joint or two somewhere rather than faulty components... just a question of where!

[aleximan]

Probing D16 cathode the speaker of my amp plays a fuzzy and bright octave effect...as you said.
Problem is the input signal on IC11/p3...signal voltage = 3.54v but the sound comes out in form of a perceptible static whistle (my 9V adapter emits this sound usually when attached to my other mooer pedal.) ...
and I agree it is probably just a cold joint somewhere before IC12...er else?...which part of the diagram comes prior IC12 and it is key? For example: The whistle is heard on both pins 6 and 7 of IC12..one louder, the other almost mute but still a whistle, no music...should I check the joints of components from D16 or other directions?...feel a bit lost. It has become such a tought maze for me to resolve...It is definitely not a project for greeners like me

[Scruffie]

Oh, okay, when you talked of a static whistle before I thought you were just talking about around D16.

So, if you probe C27, do you have a muffled representation of your input signal on both sides?

Assuming that is the case, the areas to focus on for bad joints, incorrect values etc. will be everything south of D16 anode, so R45-49, IC12 and IC11, R80-85 plus caps.

Is this your very first project then? While it doesn't involve the set up complication of a delay based effect, on sheer parts count alone, certainly a... brave choice
It may be wise after a couple more stabs at it to set it aside and come back to it once you've got a few more projects under your belt, even the experienced builders know when to take a break.