I AM A DUMMY GGG TUBE SCREAMER DEBUGGING HELP!

[yalesmith]

Hello All!  I am pulling my hair out trying to debug an Its8 build from GGG, I have built about 10 pedals in the past but nothing like this.  I have good soldering technique, but have very poor scmatic reading skills just to give you some background.  The data sheet is below so any help would be much appreaciated. 


Here is the checklist to fill out:
1.What does it do, not do, and sound like? - NO SOUND AT ALL, BYPASS WORKS BUT NOTHING WHEN ENGAGED

2.Name of the circuit = GENERAL GUITAR GADGETS ITS8 TUBE SCREAMER

3.Source of the circuit (URL of schematic or project) =
http://www.generalguitargadgets.com/pdf/ggg_its8_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
http://www.generalguitargadgets.com/pdf/ggg_its8_mods.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

4.Any modifications to the circuit? Y or N - ONLY MODIFICATION WAS THE VERY EXPENSIVE BOUNTIQUE MODIFICATION WHICH WAS AN OPTION WITH THE KIT

5.Any parts substitutions? If yes, list them. - NONE

6.Positive ground to negative ground conversion? Y or N- NO BUT NO IDEA WHAT THIS IS

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => 6.38 VOLTS

Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead = 9.36 VOLTS
Voltage at the circuit board end of the black battery lead = 0 VOLTS

2N4401 TRANSISTOR
Q1
C = 9.36
B =3.79
E =4.84

Q2
C=9.36
B=3.81
E=4.89

IC1 DUAL OP= AMP
P1 = 2.69
P2 = 0
P3 = 3.95
P4 = 0
P5 = 2.69
P6 = 0.12
P7 = 1.09
P8 = 9.36


D1
A (anode, the non-band end) = 2.09
K (cathode, the banded end) =2.69

D2A
A =2.69
K =2.40

D2B
A =2.42
K =2.10

D3 LIGHT EMITTING DIODE
BOTH CONNECTIONS  =2.69

D4 LIGHT EMITTING DIODE
BOTH CONNECTIONS  =2.69

D5
A= 0
K= 9.36

LASTLY THE LIGHT EMITTING DIODES DO NOT LIGHT UP!

[snakey]

You might want to invest in a new battery 6v is too low!

[Govmnt_Lacky]

I can only assume that you typo'd the outside battery voltage (6.38) since you list Pin 8 of IC1 as 9.36 (This pin is connected to V+)

The elephant in the room here is obviously IC1. Your voltages on pins 1-3 and 5-7 are bad. All of those pins SHOULD be around 4.5V.

Did you socket the IC chip or did you solder directly to the PCB? Here is some ideas to get you going in the right direction:

1) Triple check ALL component values, component placement/orientation, check for solder bridges, etc. (This will take some time but is VERY, VERY important!)
2) Verify your off board wiring. To include your in/out jacks, DC jack, and 3PDT stomp switch.
2) If you socketed your IC, swap it out! Then re-check voltages.

Try these then repost here with findings.


Good Luck  


BTW.... LEDs D3 and D4 WILL NOT light up because they are only there to clip the signal.

[petemoore]

  Fine work filling out the debugging page.
  Seems brutal until you learn the 'dodges 'n stops'.
  Good work may seem ''stalled'' or stuck in a sludge-still-mire.
  It is important to notice this. 
  Greater speed is attained by disciplines intened to vary the rate of movement, first: to extremely slow and focused movement.
  By developing accuracy in the slow movement, much quicker accurate-enough movements can begin.
  This may require the reading rate be stopped while reading material from related sources is attained [perhaps printed], when the comprehension rate goes to say...less than 9%. That's not a bad rate of comprehension as it naturally begins to grow once some things have been established:
  The difference between AC and DC is understood.
  Guitar puts out *tiny +/- AC Voltage Waveshapes [in the form of +/- voltage swings], AC = constantly varying voltage, can vary very fast [high frequency] or can be varying in voltage potential very very slowly [low frequency of change] such as in an LFO [phaser set to slow, the lfo slowly sweeps a voltage up/down.
  DC is like consistant pressure, a barrel full of water with a bottom tap, the pressure never varies 1 number can be assigned, say 9.2vdc.
  The basic building block circuits are sort of understood.
  The AC voltage swings ''controls the tap-valve'', and lets out various currents from the 'filled barrel' of DC potential creating *large AC waveforms, same shape as the tiny ones at the input.
  The quicksand begins to move around the top of the buried boot of the fresh Electron study.
  Capacitors block DC. The value of the capacitor and what position' it's in determine how much impedance [partial block] is applied at what frequency.
  Then there's all the AC lingo, and DC slang...impedance is an AC thing [AC jumps all over in voltage and so everything else whips around, that's why the voltage swings are often simplified by converting AC into an average potential voltage. Otherwise an 'optional' oscilloscope can display the waveforms.
  Data sheet for the active component you are using contain info you need, operating voltages and all the electronic data about the active device.
  It is best to test for non-shorted out condition of _/+ circuit rails before applying power [DMM in 'Beep Mode' = diode checker mode.
  Refer to the DMM manual to use the various measurement and test modes.
  Test that the 'voltage divider' ['google' for terminology definitions on an as needed basis] is two equal value 'resistors' in 'series', strung across the -/+ Dc power rails of the circuit. Find the 2 = value series resistors, apply power across the power rails [connect battery to effect circuit] then measure with DMM in 20vDC range: Black lead on 'ground' [we'll assign it to and call it 0.0VDC it is the 'DC reference voltage'. All other voltages are measured from Ground = 0.0vdc...in this case].
  Black lead on ground, 20vdc range, red lead where the two = value R's join...should read real near 1/2v...the bias voltage which the opamp bias is referenced to [the resistor that connects between an opamp pin and 'Vbias'...or Vb, aka '1/2v'. 
  Soon [generally not as soon as you might hope for] the estimated 9% comprehension establishes a foundation which fascilitates getting through some of the reading and equations [there are some really nice interactive online calculators]..at least enough to do effective building and debugging.

[MmmPedals]

The voltages seem alright so it's most probably a wiring problem.
Double check your wiring.
If you used any polarized caps make sure they are oriented correctly.
Make and learn to use an audio probe ("search" it). Then you can follow your signal from the input and see where it dies.

[Govmnt_Lacky]

The voltages seem alright...

The voltages on the dual opamp look right to you? Please explain why... 

[petemoore]

P1 = 2.69    OUtput, should be closer to 9v even with offset.
P2 = 0        *Not much room to swing from ground here.
P3 = 3.95    *In this case who knows and it doesn't matter/probably.
P4 = 0         Cool...ground.
P5 = 2.69    *Well toward the ground side of 1/2 of 9.36.
P6 = 0.12    This is pinned down pretty close to Gnd.
P7 = 1.09    Still near ground on this one too.
P8 = 9.36    Indicates the battery has at least 9.36vdc.
  Pin two...check to see if it's connected to ground, if so begin search for the trace-in-violation.
  Pin3...er...all three pins need to 'fall into place', which is what happens usually when the 1 bias issue gets resolved, the 'other pins' [not directly related or connected to the bias issue-problem-fixed-zone] jump to operational bias, the 1 thing throws all the pins amiss or into ballpark voltages.
  Pin 5 is having 1/4 or so of it's bias swing potential between 2.69 and ground, making 2.69 through 9.36vdc the potential swing of the opposite phase, assymetrical and doesn't leave much room to swing toward the ground side of this bias without hitting ground, 2.69v.
  Check the voltage diveder ? Then the opamp bias resistors that connect to Vbias?
   

[yalesmith]

Okay I tried a new ic and no go BUT i put the ic in opposite to what I have and I hear a fain sound.   I double checked the wiring and everything seems okay, I also double checked  the resistors and caps and they are correct values.  Also, I made an audio probe but I am st\uck on figuring out how the flow of audio should work....remember I stink at reading schematics (i am learning).  so whats next?

Thanks

[Govmnt_Lacky]

Posting pictures of your build will help alot! Just make sure they are close enough and of good quality.

[yalesmith]

take a look Tha

[twabelljr]

Could you flip the board and get a pic of the trace side?

[petemoore]

  The probe is essentially a wire for signal to go through to a monitor [amp].
  The reason for the capacitor is only to block DC.
  Imagine you cut your plugged-in-live-amp guitar cable in half.
  You touch your thumb to the end of it...audio probe.
  Add a capacitor to the center-signal wire to block DC.
  [requires stripping back the insulation/ground shielding wires/insulation of center wire.
  You'll still hear 'thumbuzz' through the signal wire and capacitor, this is the audio probe transferring signal into the amp.
  Staying away from the power supply and following the signal through the circuit:
  Find the inputs and outputs of the devices [opamp or transistor data sheets]:
  Say we're working on a transistor gain stage, we look for input into base of transistor and output from collector greater than the input.
  say we're lookinginto a buffer stage: an emitter follower..base is the input and emitter is the output, signal levels should be about 1:1.
  passive components can be used to remove 'portion's of the signal [often results in loss of signal..lol], as well as set up bias and do housekeeping like DC blocking.

[yalesmith]

i have set up a audiprobe but my issues is trying to figure out the flow of audio signal, basically the order of component i should test.

thanks

[Govmnt_Lacky]

Could you flip the board and get a pic of the trace side?

+1 

i have set up a audiprobe but my issues is trying to figure out the flow of audio signal, basically the order of component i should test.

Basically, you start at where the Input signal goes into the board and you follow the path from input to output. Use the schematic as a reference.