Debugging: Small Clone isn't chorusing

[Kablam]

Hi I'm Mauricio from Chile, I built a small clone from tonepad with no mods and no replacements, my problem is that only passes the clean signal, 0 chorus.

soo, i started to measure voltages and look the squem and layout if I made some mistake and i think that the components are in the right position, if i move the pots it sound some kind of oscillation so the lfo is working i think, but i notice a couple of things:

- There's 8,5v at the end of the red lead, but next to the 47R there's only 5v? i looked some voltages of other people and i think that my problem starts here. if i remove that resistor the components recives the right voltage.
- Q2 voltage is strange: C =5 B=0 E=0? another problem
- Q3 is hot, is that normal?

I check for cold joints but it seems to be ok, i also check with audioprobe but i can't find where the problem starts.

Here's some pics of my pcb










Now the voltages:

Battery = 8,5v

next 47R= +-5,5v

CD4047

1= 2v
2= 0v
3= 2v
4= 2v
5= 2v
6= 2v
7= 0v
8= 0v
9= 0v
10= 0v
11= 1v
12= 0v
13= 2v
14= 2v

MN3007
1= 2v
2= 1v
3= 0v
4= 0v
5= 0v
6= 0v
7= 0v
8= 0v

4558
1= 2v
2= 2v
3= 2v
4= 0v
5= 2v
6= 2v
7= 2v
8= 5v

LM358
1= 0-1(fl)v
2= 2v
3= 2v
4= 0v
5= 1v
6= 1v
7= 1-3 (fl)v
8= 5v

Q1 (left to right)
0 3 1

Q2 (left to right)
5 0 0

Q3 (down to up)
5 3 2

so thats it, sorry for my english, it isn't my native language, but please give me a hand i'm a little piss off with this project, and i don't want to leave it.

Bye!

[mcknib]

Hi Mauricio,

You'll need to put better pictures up showing the whole board both component and solder sides and try to orientate them the same way up as the build documents i.e pots at the top. I'd also put pictures of all the off board wiring to the potentiometers, jacks, DC jack, 3PDT etc your voltages are way off but as I say we can't see everything to be able to check it.

My build although not a Tonepad one had the following voltages:

Supply 9.03v

IC1 4558
1.   4.3
2.   2. 4.3
3.   3. 4.2
4.   0
5.   4.3
6.   4.3
7.   4.3
8.   8.7

IC2 MN3007
1.   8.05
2.   4
3.   4.4
4.   0
5.   0
6.   3.98
7.   4.43
8.   4.43

IC3 4047
1.   7.16
2.   0.06
3.   6.93 -7.17
4.   8.06
5.   8.04
6.   8.04
7.   0
8.   0
9.   4
10.   4
11.   4
12.   0
13.   7.92
14.   8.05

IC4 LM358
1.   0.8 to 2.5
2.   3.94
3.   3.91
4.   0
5.   0.89 to 3.4
6.   2.13
7.   0.01 to 7.4
8.   8.71

Q1. 2N5087 E. 3.86  B 3.22  C 0
Q2. 2N5088 E 3.72  B 4.28  C 8.7
Q3. 2N5088 E 8.04  B 8.67  C 8.7

Once you post the pictures of the whole pcb we can look and see if any components are the wrong way round, check values etc.
When you say you only get clean sound do you mean in effects mode or bypass mode or both.

I'm taking it you've already tried adjusting the trimmer to bias the output from the 4558 you can do it by ear and hear the chorusing it may well be that this is where your problem starts sending the wrong voltages to the rest of the circuit . Double check your 47R is indeed a 47R and check IC's and transistors are located firmly into their sockets

[Kablam]

thank for the answer, i don't know why the pictures doesn't show complete, if you right click the image you'll be able to see the entire pcb.

i'm testing this pedal without any external component (switch, dc jack) only pots an a 9v clip and audio jacks in my test box, the signal passes very clear and cleary but with no modulation
with the trimmer do you use a single turn trimmer or a multiturn?  is there any change with that?

The 47R resistor decreases a lot the voltage, today i removed it and the voltage turn to 8,3v but no results. and also i can see that my voltages are proportional with the amount that recieves, making a comparison with your pedal.

Thanks for you help!

[Keppy]

The voltage drop across the 47R probably because the circuit is drawing too much current.

Your readings would be more meaningful measuring to tenths of volts, rather than whole volts. Your transistor voltages are definitely off. Q3, especially. Try removing Q3 from the socket and measure the voltages on the socket pins. The center one (base) and lower one (collector) should equal the power supply at the end of the 47R resistor. You can try this with other transistors and ICs as well, to find out which of those (if any) is drawing current and causing the power supply to drop to 5v.

I can't see D1 very well. Is it oriented correctly? It feeds the input to the delay chip. The input (pin 3) and outputs (7, of that chip have no voltage, so there is no signal through the delay chip. The trimpot can adjust that, but it's unlikely to work well until your power supply is up around 9v.

[mcknib]

You should turn the trimmer through it's range until you hear a chorusing sound then leave it at the spot where it's most pronounced the so called' sweet spot'.

Although I'm not fully aware of this circuit it looks to me like the 100K trimmer would be to set the bias voltage 4.5V for some stages of the circuit.

If you get no chorusing throughout the trimmers range then you could check some of the Voltage References around were you suspect the problem to be

In the build docs there are lots of Voltage Reference points 4.5V and +9V (if you look at the pcb image in the build docs the red line shows you what should be getting power supply e.g pin 8 of the 4558 collector of Q2 and 3 etc.) check you're getting power supply and check your 4.5V references the first one I would check with your 47R in circuit (making sure your 47R is ok with your meter although very rare a resistor is defective.) is on the top left in the power supply where there are 2 x 56K resistors forming a voltage divider and the 10uF electrolytic going to ground you'll see the +4.5V and that's were you should check with your meter to see if you get 4.5V there. There does seem to be a problem with current draw somewhere. 

Have you checked your voltages with the IC's and transistors out of socket

[Kablam]

Thanks for your answers guys! i really got a "stomp blindness" with this pcb, i will measure again transistors and ic's

and the diodes are in the right way, i will post again with my results.

[mcknib]

Sorry Keppy takes me forever to type especially with schems and build docs open I'm slower than paint drying!

[Kablam]

Update:

I removed all active components and remeasure the pcb, next 47R the votaje is 8v so i think that is a problem with ic's because i put the transistors and they have the right voltajes (arround 8v q2 & q3, and 4v q1).

i'm close to the solution i think

Saludos!

[mcknib]

Try removing the IC's from the sockets and see what the voltages are this will help track down the problem IC if that's what's causing it with only 5V on the 4558 power supply pin 8 in socket see what you get with it out of socket if you're getting 8V either side of the 47R with your power supply at 8.5V that would be right the drop on mine is also 0.5V so if you get that with the 4558 out of socket that'll be hopefully your only problem.

If you get good readings with an IC out of socket that'll tell you it's more than likely faulty and the circuit around it's alright if not then it's probably in the circuit but at least you'll narrow down which part the fault is in, Keppy is far more knowledgeable than I am on this circuit and has pointed you in the right direction and I'm happy I've learnt something, so hopefully as you say you're nearly there.

[Kablam]

indeed my friend, i always learn something new 

OK, the problem is MN3007! i test the pcb without it and the voltages are ok, but when i put the MN.. paf... 5v and the mn has values like 3v pin 1 and 0v arround 5 pins.. China stuff.

the measures of the MN socket are: (i know that is no good measure entire volts, but i lost my multimeter i know im reading with an old multi  )

1= 7 v
2= 3 v
3= 6 v
4= 0 v
5= 0 v
6= 3 v
7= 7 v
8= 7 v

And the rest of pcb has good voltages (4,5 v on pin5 of 4558, q3 is not hot, q2 has more than 0v)

so i have to wait now because there's no stock of MN in Chile, thanks for your responses, they cleared my mess

[mcknib]

Great glad you found it 9/10 times it's usually a faulty MN3007 or not turning the trimmer to set the chorusing or some builds like mine have two grounds to help stop clock noise that sometimes causes problems.

You're readings on the 47R kinda threw me a bit so I'm glad Keppy came in and got you on the right track and I learnt something so cheers Keppy, more eyes are better than one pair and sometimes you can overlook something even if it's staring you right in the face.

I remember audio probing a circuit plugging my probe into the amp input and not being able to get it in so I duly pulled it out and put it in the other input and got no audio not even at the in pad after hours of frustration I pulled it out tried the other input couldn't get it in again so stripped the amp down to check the sockets and there it was the end had broken off the probes jack and lodged in the input, if only I'd looked at the probe jack I'd have saved myself hours of frustration and my neighbours having to listen to my loud cursing haha anyway a lesson learned I always start with the basics now power to pcb etc.

I'll PM you with a good source for fully tested MN3007's don't want to break any forum rules for advertising

[Keppy]

Well, it's a bummer that the problem is the most expensive component, but I'm glad you found it!

Those voltages look pretty good to me, so it seems like the problem is most likely within the chip and not the surroundings. 7v on the supply to the chip seems a little low, but not by much, especially when rounding to whole volts. I hope you find a replacement BBD soon!

[Kablam]

Well, it's a bummer that the problem is the most expensive component, but I'm glad you found it!

Those voltages look pretty good to me, so it seems like the problem is most likely within the chip and not the surroundings. 7v on the supply to the chip seems a little low, but not by much, especially when rounding to whole volts. I hope you find a replacement BBD soon!

yeaah, it's really annoying that the problem is the  MN  but what can i do..

i know that 7v it's low for the pcb, i was testing it with a duracell but i suppose that i left the fx on too much..

what a great forum also i can practice my lame english jejeje.

Saludos!