Debug: No chorus from Small Clone

[Keeb]

Let me start off by saying that this is a great forum. I have been reading a lot and this is my first post.
Unfortunately it's a debug thread.

I have read the thread http://www.diystompboxes.com/smfforum/index.php?topic=74074.0 but no luck.

So here goes:

Project: Tonepad Small Clone / Heladito
Schematic: http://www.tonepad.com/getFile.asp?id=97
Mods: No. I haven't wired a switch, everything goes directly into the board.
What does it sounds like: Signal goes through clearly but no chorus.

Values:

Battery: 9.36V

CD4047
8,40
0.07
7,73
8,53
8,54
8,54
0
0
0
4,28
4,28
0
8,40
8,53

MN3007

8,53
4,27
4,49 (according to http://www.axecentral.com/small-clone-repair-notes-9312610.html)
0
0
4,27
5
5

LM348
1,75
4,5
3,84
0
2,24
2,13
4,10-4,20
4,10-418

4558
4,60
4,60
0
0
4,55
4,57
4,53
9,10

D1
A: 5,1
K: 4,55

D2
A: 0.07
K: 7,66

Q1
C: 0
B: 3,75
E: 4,54

Q2
C: 9,08
B: 4,54
E: 4,38

Q3
C: 9,10
B: 8,96
E: 8,44

[rustypinto]

How much have you tweaked the trim pot? This sets the bias on the MN3007, which determines if the chorused signal gets passed through. Its usually not obvious if the bias is at the correct voltage from your MN3007/pin 3 measurement. The best way to do this is go through the entire sweep of the trim while constantly strumming your guitar (or any constant signal through it) until you start to hear chorusing.

[GP]

I think you mean LM358 rather than 348... well, at least i hope you do because you'd be hard pushed to solder 14 pins in that space 

Pin 8 of the LM358 should be at V+ so it tends to imply you have a short between pin 7 and 8. I'd check that if i were you. This opamp is the LFO and without that working, you'll get no chorus.
Q2 doesn't look right either so maybe you've got that one soldered in the wrong way round?

[Keeb]

Thanks a lot for your replies guys!

Yeah, I meant the LM358  .

Q2 seems fine to me (I mean the schematic shows that the collecter has +9V right?)
I checked again and pin 8 has V+.
I tried the trimpot and nothing.

Ideas?

[GP]

Q2's base should be about 0.6V above the emitter to work correctly. I suspect you have it the wrong way round or a short between base and emitter, perhaps. It's all very well you saying there should be 9 volt on the collector but, if you have the pin out incorrect, how can you be sure that it's the collector at 9V?

[Keeb]

Q2's base should be about 0.6V above the emitter to work correctly. I suspect you have it the wrong way round or a short between base and emitter, perhaps. It's all very well you saying there should be 9 volt on the collector but, if you have the pin out incorrect, how can you be sure that it's the collector at 9V?

Thanks!
http://se.mouser.com/Search/ProductDetail.aspx?R=2N5088_J61Zvirtualkey51210000virtualkey512-2N5088_J61Z
that is the 2N5088 I used and I placed it with round side towards the 4558 (as the instructions from tonepad) which should mean I have the collector in the middle of the board (according to the datasheet).

I tried to audio probe the thing and got cleans. Where should I probe to check the chorus? (I'm not great at schematics).

Edit; I checked for shorts around the Q2 but couldn't find any.

[GP]

Ok.. assuming you do actually have a Fairchild 2n5088 you should have placed it the way you have. does it have a little "f" logo on it?

Can you recheck your voltages of the LM358 please... at least 3 of the pins should be varying in voltage (pins 1, 5 and 7)... this opamp is the LFO and, as i said before, if this isn't working there will be no chorus.

I'd probably be probing around Q2's base or emitter because that's where i'd expect the delayed signal to be... but i don't think you're going to hear anything conclusive because, on the face of your posted voltages, your LFO isn't working.

[Keeb]

Ok.. assuming you do actually have a Fairchild 2n5088 you should have placed it the way you have. does it have a little "f" logo on it?

Can you recheck your voltages of the LM358 please... at least 3 of the pins should be varying in voltage (pins 1, 5 and 7)... this opamp is the LFO and, as i said before, if this isn't working there will be no chorus.

I'd probably be probing around Q2's base or emitter because that's where i'd expect the delayed signal to be... but i don't think you're going to hear anything conclusive because, on the face of your posted voltages, your LFO isn't working.

Okay.
I remeasured and I don't know what I did last time because here's what I got:
LM358
1. 1,36-2,25
2. 4,06
3. 3,75
4. 0
5. 1,66-2,80
6. 2,09
7. 1,17-6,83
8. 8,95

Yes, there is an F on the transistor as well.
Right after I measured the values I played my guitar through but still no chorus. I tried adjusting the trimpot whilst playing but no cigar.

[GP]

Hey... don't be disheartened...

your LFO appears to be working ok so that's a start. The voltages are varing on the pins i pointed to and you ought to be able to change the speed of the sweep with the "rate" pot.

did you try audio probing around Q2? what did you find? given you have a working LFO, you ought to be able to hear a modulated signal at Q2.... I've never built a small clone but i'd imagine you'd get a vibrato effect at Q2. If you don't find a modulated signal there, try tweaking the trimpot (very slowly and precisely) until you do.

I still think your voltages at Q2 look(ed) wrong so you might want to take a magnifying glass to the solder side of the board and check you don't have any hairline shorts anywhere. It will only take a miniscule amount of solder to create a short circuit and ruin everything for you. Maybe you could post a (detailed) photo of the solder side so we can look at it too?

Just to be clear about my methodology... after Q2 is where the modulated signal is going to get mixed into the clean signal. If you don't hear any chorus, this is the point where we should start investigating.

[Keeb]

Got it to work!

I followed your advice and audio probed around Q2 and got nothing, no sound at all. So I realised the problem must be earlier in the circuit and decided to check the schematic and layout. I see that I have forgotten a jumper!
Put that in place and tried. Nothing.
Adjusted the trimpot and BOOM!

Thank you so much for all your help GP (and most of all your patience!).
This was a really learnful experience!

[GP]

That's great news! Glad you got it working and it was a pleasure helping you.

[JPSH79]

"Warning: this topic has not been posted in for at least 120 days.
Unless you're sure you want to reply, please consider starting a new topic. "


I have similar problem with my Heladito but the solution unfortunately isn't the same.
Pcb is self-etched but it should be ok since I have gone through it many times now with continuity tester.

I made the pulsating LED -mod to see if the LFO is working and apparently it isn't since the led is constantly on and not blinking.

I have no chorused sound coming out. Depth- and rate-controls are also behaving weirdly. In certain combinations of their positions I get very high pitched sound and sometimes kind of motorboating sound. When I turn the depth-pot the outcoming signal seems to have someking of phase shifting thing going on, but as soon as I stop turning it the effect goes away.

I've searched the forum inside out but didn't find any info about how to fix the problem with missing LFO.
Could someone please check if these voltages are what they should be and

Here are my voltage readings with battery output of 8.33v. (7.27v after the 47 ohm resistor):

LM358

pin1  4.66
pin2  2.22
pin3  3.28
pin4  0
pin5  0.27
pin6  1.79
pin7  0.257
pin8  7.24



4558

pin1  3.66
pin2  3.66
pin3  3.58
pin4  0
pin5  3.62
pin6  3.62
pin7  3.62
pin8  7.23


MN3007

pin1   6.61
pin2   3.28
pin3   6.57
pin4   0
pin5   0
pin6   3.67
pin7   5.38
pin8   5.38


CD4047

pin1   6.46
pin2   0.085
pin3   5.57
pin4   6.6
pin5   6.6
pin6   6.6
pin7   0
pin8   0
pin9   0
pin10  3.26
pin11  3.27
pin12  0
pin13  6.46
pin14  6.59


Q1

e  6.33
b  6.15
c  0


Q2

e  4.69
b  5.24
c  7.20


Q3

e  6.59
b  7.19
c  7.21