small stone 1 color switch mode not working

[chromesphere]

Hi All,

I have built 2 small stones.  One of them works perfectly.  The other has a slight problem.  I perviously posted the problem could be linear pot related. Changing the pot to log, didnt fix it, and since i've tested the 2nd small stone which is using a linear pot and working perfectly, there is something wrong with this one.

The problem is, one of the color switch settings works fine, no problems, but the other color switch setting (I think its the stronger setting), 90% of the pot turn is just a clean signal with no audible effect...The last 10% of the pot turn, the effect kicks in, sounding normal even changing speed as i adjust it in the last part of the rotation, but i can't get 'slow' swooshing, only fast speeds.  As you turn back around, the effect fades out.

I have checked over the board...countless times.  Theres no bridges, the resistor values / cap values are all correct.  I've tried swapping the PNP transistors and the IC with the working board, nothing has worked as yet. It looks like the LFO is working properly, it just cuts out in the 2nd mode...

Anyone have any ideas of what i could try replacing or focusing on?  If i had to guess, it sounds like theres a resistor in the 2nd part of the circuit when i flick the switch thats incorrect (or capicator) causing the pot to react incorrectly, but i've checked all the values about 10 times and they are all fine...I've also tried replacing the .1uf and 33uf caps near IC5 as a long shot but this didnt fix the problem.

Any help would be hugely appreciated.

Please let me know if you need any other voltage readings too.

Thanks guys,
CS

[chromesphere]

Ok, just quickly checked against the working small stone,  Its the dry effect, ie the lesser effect, that's not working properly.

CS

[chromesphere]

Or would anyone have or be able to point me to a list of component voltages, that i could compare my unit with to try and work out which component is causing the problem?

[oskar]

If you link to the project/ schematic it's easier to follow what you're doing.
Check out the sticky "What to do when it doesn't work".

Or would anyone have or be able to point me to a list of component voltages...

Post the voltages you've got instead. The voltages you can find is if you search the forum for earlier posts on the small stone.
Normally you don't have specified voltages. It is either more or less obvious from the schematics what it is supposed to be. Sometimes transistors bias voltages are specified.

[chromesphere]

Hi Oskar,

Sorry for the long post.  Wanting to supply as much info as i could...

Thanks for the info, you have actually pointed me in the right direction (please see below).

I've think i've found something; the 5th IC or LFO isn't functioning, at all, when the pot is in the first 90% of dry mode.

Heres my readings for all IC's and Transistors with the pot fully turned to the 'slowest' setting, for both wet and dry mode:

Note: voltages dont move much.  In wet mode, they start to move as soon as i turn the pot just a fraction, but nothing for the first 90% of dry mode.

---------------------------

In wet mode (working properly as far as i can tell)

IC1-4

1 - 0v
2 - 3.02v
3 - 3.02v
4 - 0v
5 - 0.65v
6 - 3.95v
7 - 7.33v
8 - 0v

IC5

1 - 0v
2 - 4.74v
3 - 4.64v
4 - 0v
5 - 0.67v
6 - 1.74v
7 - 7.27v
8 - 0v

q1
c - 2.42v
b - 2.72v
e - 6.67v

q2 (bc559 pnp)
c - 7.26v
b - 6.67v
e - 4.52v

q3
c - 3.67v
b - 3.99v
e - 7.24v

q4
c - 3.13v
b - 3.67v
e - 7.27v

q5
c - 3.57v
b - 3.92v
e - 7.24v

q6
c - 3.03v
b - 3.57v
e - 7.27v

q7
c - 3.62v
b - 3.97v
e - 7.23v

q8
c - 3.08v
b - 3.62v
e - 7.26v

q9
c - 3.61v
b - 3.95v
e - 7.23v

q10
c - 3.04v
b - 3.58v
e - 7.27v

q11
e - 4.73v
b - 4.65v
c - 5v

q12 (bc559 pnp)
e - 4.74v
b - 4.74v
c - 5.06v

q13 (bc559 pnp)

c - 1.23v
b - 1.73v
e - 7.23v

q14
c - 0.67v
b - 1.23v
e - 4.64v

---------------------------------------------

In dry mode.

IC1-4 (all almost exactly the same, varying only in a couple of milli-volts)

1 - 0v
2 - 2.99 - 3.01v
3 - 2.99 - 3.01v
4 - 0v
5 - 0.64 - 0.66v
6 - 4 - 4.06v
7 - 7.44v - 7.54v
8 - 0v

ic5 (now this looks like the problem - ive tried replacing the chip, still get the same readings)

1 - 0v
2 - 0v
3 - 0v
4 - 0v
5 - 0v
6 - .1v
7 - 0v
9 - 0v

q1
c - 2.34v
b - 2.74v
e - 6.77v

q2 (pnp)
e - 4.39v
b - 6.77v
c - 7.37v

q3
c - 7.33v
b - 4v
e - 3.52

q4
c - 2.95v
b - 7.16v
e - 7.36v

q5
c - 3.47v
b - 3.95v
e - 7.34v

q6
c - 2.90v
b - 3.47v
e - 7.37v

q7
c - 3.52v
b - 4v
e - 2.85v

q8
c - 2.94v
b - 3.52v
e - 7.36v

q9
c - 3.94v
b - 3.98v
e - 7.33v

q10
c - 2.91v
b - 3.5v
e - 7.36v

q11 (pnp)
e - 5.1v
b - 5v
c - 5.4v

q12 (pnp)
e - 5.1v
b - 5.1v
c - 5.4v

q13
c - 1.22v
b - 1.71v
e - 7.34v

q14
c - .66v
b - 1.22v
e - 5v

I hope all those c b e's are correct.

Thanks for taking the time to help.

CS

[oskar]

Here are your voltages side by side.

Important first

q11      q11 (pnp)
e - 4.73v      e - 5.1v
b - 4.65v      b - 5v
c - 5v      c - 5.4v

q12 (bc559 pnp)      q12 (pnp)
e - 4.74v      e - 5.1v
b - 4.74v      b - 5.1v
c - 5.06v      c - 5.4v

I think you have a short here. Q12 emitter and base!
The problem is probably in booth modes but you only notice it in one mode because throwing the switch exaggerates the error (just guessing).
Measure resistance between q12 base and emitter.

IC1-4      

1 - 0v      1 - 0v
2 - 3.02v      2 - 2.99 - 3.01v
3 - 3.02v      3 - 2.99 - 3.01v
4 - 0v      4 - 0v
5 - 0.65v      5 - 0.64 - 0.66v
6 - 3.95v      6 - 4 - 4.06v
7 - 7.33v      7 - 7.44v - 7.54v
8 - 0v      8 - 0v

Looks good.

IC5      

1 - 0v      1 - 0v
2 - 4.74v      2 - 0v
3 - 4.64v      3 - 0v
4 - 0v      4 - 0v
5 - 0.67v      5 - 0v
6 - 1.74v      6 - .1v
7 - 7.27v      7 - 0v
8 - 0v      9 - 0v

Looks ungood.
This is like crazy. If you loose all poser and signal like this, whatever is wrong should affect the whole circuitboard?!
In the right collumn the voltages looks acceptable. If you didn't ground the probe pin marked com properly this is probably what you could expect. Redo please...

q1       q1
c - 2.42v       c - 2.34v
b - 2.72v      b - 2.74v
e - 6.67v      e - 6.77v

q2 (bc559 pnp)      q2 (pnp)
c - 7.26v      e - 4.39v
b - 6.67v      b - 6.77v
e - 4.52v      c - 7.37v

Looks good and also we now that the input works allready.
You've reversed c and e with q1

q3      q3
c - 3.67v      c - 7.33v
b - 3.99v      b - 4v
e - 7.24v      e - 3.52

q4      q4
c - 3.13v      c - 2.95v
b - 3.67v      b - 7.16v
e - 7.27v      e - 7.36v

q5      q5
c - 3.57v      c - 3.47v
b - 3.92v      b - 3.95v
e - 7.24v      e - 7.34v

q6      q6
c - 3.03v      c - 2.90v
b - 3.57v      b - 3.47v
e - 7.27v      e - 7.37v

q7      q7
c - 3.62v      c - 3.52v
b - 3.97v      b - 4v
e - 7.23v      e - 2.85v

q8      q8
c - 3.08v      c - 2.94v
b - 3.62v      b - 3.52v
e - 7.26v      e - 7.36v

Looks ok. If e is the lowest of the given values... and nothing else.   

q9      q9
c - 3.61v      c - 3.94v
b - 3.95v      b - 3.98v
e - 7.23v      e - 7.33v

Again wrong notation and the right column bad values.
q 3,5,7 and 9 are configured the exact same way so they should have the same voltages which consequently have been:
c ~7.2
b ~4
e ~3.5
So q9 emitter (which you call collector) voltage in the right collumn is bad but I think it's a freak thing. If you measure again you'll probably see 3.5V

q10      q10
c - 3.04v      c - 2.91v
b - 3.58v      b - 3.5v
e - 7.27v      e - 7.36v

good

q13 (bc559 pnp)   <--------------------------- NPN   
c - 1.23v      c - 1.22v
b - 1.73v      b - 1.71v
e - 7.23v      e - 7.34v

At least your consequent     (c ~7.2, e ~1.2)

q14      q14
c - 0.67v      c - .66v
b - 1.23v      b - 1.22v
e - 4.64v      e - 5v

I'ld really expect these volts to move around more...


I'm going for coffee now. I deserve it...   

[chromesphere]

Hi again Oskar,

thanks again so much for your time.

Ok i hope i've answered your questions here...

Before i give you the voltages, I scratched around q12 on the underside (for about the 5th time), not sure if this is a result of that, but now, i start the pot on fully low, the effects speed is the fastest shimmering, i turn the pot and it starts to slow down, up till half way of the pot turn, then i keep going, and the effect starts to get fast again!  I kid you not! There are 2 'fast' settings on the pot at either end...


I rechecked ic5, i must have stuffed up.  here are the REAL voltages :-)

IC5 (pot fully anti-clockwise - dry effect)
1 0
2 4.57 - 4.61
3 4.46 - 4.51
4 0
5 0.67
6 1.72
7 6.77 - 6.78
8 0

IC5 Dry effect fully clockwise
1 0
2 4.57 - 4.60
3 4.47 - 4.5
4 0
5 0.66-.67
6 1.71
7 6.76 - 6.77
8 0

IC5 Dry Effect Half Way (approx)
1 0
2 2.1 - 5.7
3 2.1 - 5.7
4 0
5 0.57
6 1.62 - 1.82
7 6.3 - 7
8 0


-------------------------------

IC5 wet effect fully clockwise
1 0
2 4.23 - 4.31
3 4.12 - 4.24
4 0
5 0.67
6 1.72
7 6.69 - 6.71
8 0

ic5 wet effect fully anticlockwise
1 0
2 4.21 - 4.34
3 4.14 - 4.23
4 0
5 .67
6 1.72
7 6.69 - 6.71
8 0

IC5 wet Effect Half Way (approx)
1 0
2 3.3 - 5.6
3 3.3 - 5.6
4 0
5 0.57
6 1.66 - 1.79
7 6.6 - 7
8 0

I've retested q9 q5 q3 and recieved these values:

pot clockwise dry effect

Voltages dont vary

e - 6.96
b - 3.75
c - 3.27

pot anti-clockwise
e - 6.67
b - 3.71
c - 3.2 - 3.4

pot half way
e 6.3 - 7
b 3.56 - 3.8
c 3 - 3.7

i noticed on q7, the collector and base voltages were eratic in the half way position, oscillating sometimes around the values of q3 5 and 9, and sometimes between 1.5 and 3v (base 2v - 3.5v). and in the fully turned position, collector 2.5v and base 3v relatively stable (0.5v less then the other transistors).  The readings would sometimes revert to the correct ones temporarily, but then go back to incorrect. I then tested the other 'partner' transitors (10,8,6,4) and found that q8 im assuming being q7's 'partner' is also showing a loose of .5v on base and collector (2.5v and 2 respectively). Tapping the board encourages the voltages to jump all over the place (loose component)?  Maybe whatever is supplying q7 and 8 the voltage is faulty or loose?

The resistance for q12 base and emitter = 21.6k

q14 behaves the same way, voltage wise, in this, varyings more when the pot is centered, but doesnt varying much / at all when the pot is left most or right most...

q14
pot clockwise (and anticlockwise -> the same)
e 4.1 - 4.22
b 1.23
c 0.67

pot middle
e 0.6 - 0.74
b 1.13 - 1.33
c 2 - 5.8

Thanks again for your help Oskar!
CS

[oskar]

http://www.tonepad.com/getFile.asp?id=7

Progress... we hope.   
Your discipline on the DVM is nothing but amazing.

Before i give you the voltages, I scratched around q12 on the underside (for about the 5th time), not sure if this is a result of that, but now, i start the pot on fully low, the effects speed is the fastest shimmering, i turn the pot and it starts to slow down, up till half way of the pot turn, then i keep going, and the effect starts to get fast again!  I kid you not! There are 2 'fast' settings on the pot at either end...

I allways try and confirm a short first. Redo/tidy up Q11/Q12 soldering.

i noticed on q7, the collector and base voltages were eratic in the half way position, oscillating...

If Q7 ain't behaving it would affect the sound but you get phasing so we settle with this for now and focus on the LFO.

The resistance for q12 base and emitter = 21.6k

It is very hard to measure resistances in a circuit. You get transistors and capacitors to interract and it's hard to know what you really are measuring.

What is the voltage across the rate pot?

[chromesphere]

Hi Oskar,

ignor my comments about q7, 8.  I resoldered a resistor and cap nearby them and now, 'all of a sudden' they are working correctly again (no voltage drop). So dont need to worry about that anymore, hopefully.

So the only problem at the moment is this strange rate pot behaviour, being fast at both ends and slow in the middle.  I'll measure the rate pot voltage and redo soldering for q11 and q12 tonight, and anything else that looks suspect and post results tonight.

I can't believe how much trouble this board has been...

Thanks again.

CS

[chromesphere]

Ok, measured the voltage at the pot leads (both voltage readings are the same at the single pot lead and at the 2 that join together). 

Did you want to me measure across the pot or the way i've been doing it so far, Com to batt negative and pock around with the red / plus probe on the board?  The later being what i did to get these measurements:

Pot Anti-clockwise: 0.67v
Pot Middle: 1.41 - 1.49v
Pot Clockwise: 0.67v

I will check soldering of q11 and q12 tonight.

CS

[oskar]

Ok, measured the voltage at the pot leads (both voltage readings are the same at the single pot lead and at the 2 that join together). 



Pot Anti-clockwise: 0.67v
Pot Middle: 1.41 - 1.49v
Pot Clockwise: 0.67v

CS

From pin 5 of the OTA(3080) there is a diode forward voltage drop. ~0.7V
This is almost a fixed value but it will vary a bit with the current. The higher current the higher voltage you will see.

Did you want to me measure across the pot or the way i've been doing it so far, Com to batt negative and pock around with the red / plus probe on the board?  The later being what i did to get these measurements:

As you've noticed by now voltage is a relative question. It is something measured between two points. When I asked you for the voltage across the pot I really didn't care in what form the answer would come. Partly because I mostly can figure out myself what the voltages relate to and partly because I'm used to get all funny kinds of voltages given when I ask and last but not least... geeeee buddy... I'm not sure really    it basically seemed like a good thing to ask...    I ask a lot of questions that I think I perhaps could find useful in the future but I'm not really sure...
Since I know that there is 0.7V from pin5 to ground and the other end of the pot see a voltage divider 27k/7k5 and the V+ is 6.7V we can calculate that the voltage from ground on one side of the pot should be ~0.7 and the other 6.7x7.5/(27+7.5)=6.7x7.5/34.5=6.7x0.2=~1.5V
6.7V is V+ as you've recorded and the other number the resistances involved.
Across the pot (when you literally put the probes in one side of it) you then see 0V whith the pot ccw (shorted) and 1.5 (divider) - 0.7 (pin5) = 0.8V when pot is fully cw. This is the expected values.
The math involved is super simple. Especially since we know that pin 5 is allmost constant ~0.7V

From
Pot Anti-clockwise: 0.67v   <------ Badass pin 5V looks super cool
Pot Middle: 1.41 - 1.49v <------ yo! Other side voltage!
Pot Clockwise: 0.67v      <----- ? ...wtf???   ...Ah! The pot is now completely ccw/shorted so the voltage divider is being pulled down by the 0.7 voltage drop by the diode ( it really is a transistor b/e junction ) Which ultimately also is part of the divider...

I choosed to give you a slightly more elaborate and hopefully pedagogic answer because this is information I've found useful myself before.

Ps. The pot and IC5 is totally cool...

I will check soldering of q11 and q12 tonight.

Your way to fame and fortune...

[chromesphere]

I sort of get some of what your were saying although i had to read it 10 times over

I have tried replacing q11 and 12 with transistors from the working board before, but didnt find any change.  I will try it again, and recheck soldering, although i'm sure i have done this as well.  I'll check closely again.

Thanks so much Oskar.

[oskar]

I sort of get some of what your were saying although i had to read it 10 times over

If you don't succeed at first mr. Wint!...

I have tried replacing q11 and 12 with transistors from the working board before, but didnt find any change.  I will try it again, and recheck soldering, although i'm sure i have done this as well.  I'll check closely again.

If you've tried this before then Q11/Q12 just ain't the problem aight! We have to look elsewhere...

Ooops!!!   

Pot Anti-clockwise: 0.67v
Pot Middle: 1.41 - 1.49v
Pot Clockwise: 0.67v

This actually needs a second walkthrough!?

If the voltages are taken com to ground and other probe to the same point on the pot then we've got an issue.
Pot Anti-clockwise: 0.67v 
Pot Middle: 1.41 - 1.49v
Pot Clockwise: 0.67v

The pin5 side of the pot is as I've ranted about ~0.7
The other side is supposed to be 1.5 with pot cw and 0.7 ccw.

did you measure from the same point on the pot?
How is the pot wired? You would get these values if the pot is wired middle to the divider and the outer lugs both connected to pin 5...

[oskar]

So the only problem at the moment is this strange rate pot behaviour, being fast at both ends and slow in the middle.

Yeah. This also is a hint that the pot is wired wrong... Maybe the lugs don't work the way you thought?
The wiper and one of the outer lugs should be wired together... normally! But some pots have a different pinout.

[chromesphere]

So the voltages are all correct, but im receiving the low voltage in the middle of the pot, and the high voltage at either end of the pot...?  Thats got to be a first 

I measured the pot with common on the DMM connected to ground on the battery and probed the tabs on the pot with the red lead.

I'm 99% sure that i've wired the pot straight from the board, no funny business / criss-crossing etc.  Just straight up to the tabs on the pot.  I'll recheck this tonight.  Sometimes you just never know.  It would explain why its behaving this way. 

(I'll check the pinout on the pot too as you just mentioned)

Thanks.

[chromesphere]

Hi Oskar,

Good news!  It WAS the wiring on the pot.  There was alot of funny business going on wired it up all over the place.  Once i rewired it, the pot action was back to how it should have been, low at one end, high at the other end. FIXED!!!

I think we have solved a number of problems with this board: 1) the original problem, 2nd switch in dry mode 90% clean before effect starts, which kind of disappeared on its own.... 2) low / irregular voltage on q7 + q8 and 3) pot wired in the wrong orientation.

So now it works!!   

+1 respect to you Oskar, for spending your free time to help a stranger.

Thanks so much.

CS

[oskar]

2) low / irregular voltage on q7 + q8 and 3) pot wired in the wrong orientation.

Now this is a problem. Actually the constructors nightmare.
Hadn't you been persistent on the voltages, chances are the effect would have worked (because it was doing phasing), but with a weaker phasing sound than than intended, and it would have disappointed you.
The good errors are when a component starts burning and the unit just drops dead.

Congratulations on a fine build. I love the small stone...   



Oskar

[chromesphere]

Yeah i was thinking that.  I wouldn't have had a clue why the 2nd sounds difference (weaker) then the first. 

It's also made me think (believe it or not). Now that i have some idea about some of the voltages around the circuit (thanks to you) i'm going to test the first SS and make sure it isn't misbehaving in any way either. 

Oh, heres a picture of the finished product (wired it up last night). 

Oskar meet my SS, SS meet Oskar:



Thanks again, couldnt have done it without your help.

CS