EHX Small Clone Vero not working

[freshmex18]

I built this layout

https://tagboardeffects.blogspot.com/2014/06/ehx-small-clone.html

and it is not working.  All I get is dry signal.  There is a slight high-pitched whine that turning the knobs affects but that's it. 

I tore the whole thing down and made a new board and it's the exact same result.  I measured every resistor and they are all correct.  I've been over the layout three times and every part is in the right place.  Reflowed every joint.  Knifed the tracks three times.  Swapped in a new MN3007 and CD4047BD and nothing different.

Help me, forum posters; you're my only hope


Q1 5087

C 0
B 4.66
E 5.37

Q2 5088

C 8.82
B 7.84
E 7.32

Q3 5088

C 8.82
B 8.21
E 8.21

IC 1 4558

1 4.43
2 4.43
3 4.32
4 0
5 4.41
6 4.43
7 4.42
8 8.82


IC 2 MN3007

1 8.21
2 0
3 5.90
4 0
5 0
6 8.21
7 6.90
8 6.93

IC 3 CD4047BD

1 8.19
2 0
3 8.20
4 8.21
5 8.21
6 8.21
7 0
8 0
9 0
10 8.21
11 0
12 0
13 8.21
14 8.21

IC 4 LM348

1 Fluctuates between 0.7 and 7.4
2 2.18
3 2.12
4 0
5 3.99
6 4.02
7 Fluctuates between 1.30 and 2.30
8 8.82

[duck_arse]

............. the circuit diagram? ..............

[duck_arse]

is Q2 base too high? connected thru resistors to pins 7 and 8, showing 6V9, it can't be higher than that.

circuit diagram?

[ElectricDruid]

Without checking *super* carefully, the chip voltages all look pretty good. Certainly nothing leaps out. And I see from the pictures that the MN3007 is a modern Xvive clone, so that should be ok - better than a dodgy eBay "original" panasonic MN3007 which is actually a 555 timer with some new name printed on the top.

Like Duck said, I'd want a circuit diagram, and then I'd start audio probing to see how far the signal gets. There's that bias trimmer that needs setting up correctly too. You won't get any wet signal if that's way out.

[freshmex18]

There is no schematic on the tagboard site.  Here is one I found on this forum




the MN3007 is from Smallbear so reliable for the most part

I adjusted the trimmer through the entire range and nothing

[freshmex18]

Tested with an audio probe.  Signal goes into the 3rd pin of the MN3007 but no signal out.  Tried the chip from my Electric Mistress that I know works and same thing.

[Matthew Sanford]

I'm confused on your mn3007 values, the datasheet I found shows pin 1 ground and pin 5 VCC, but your values are opposite that.

[ElectricDruid]

I'm confused on your mn3007 values, the datasheet I found shows pin 1 ground and pin 5 VCC, but your values are opposite that.

That's a classic. The chip uses a negative supply (-15V typical) so it's pretty common to see it used with the supply pins reversed like here (9V to "Ground", and Ground to "-15V").

[ElectricDruid]

Tested with an audio probe.  Signal goes into the 3rd pin of the MN3007 but no signal out.  Tried the chip from my Electric Mistress that I know works and same thing.

Ok, so if the BBD is a known-good device and the bias is tested, the next-most-obvious reason no sound is coming out is that the clock isn't working.
Have you got any way you can check the frequency on the 4047?

[freshmex18]

duck_arse

Looks like you are correct.  Someone in the comments on Tagboard posted the voltages for a working unit and the base and emitter should be way lower.  How would I go about fixing that?

V+
9.468

2N5087 - Q1
C 0
B 3.07
E 3.7

2N5088 - Q2
C 9.468
B 3.93
E 3.355

2N5088 - Q3
C 9.468
B 9.425
E 8.8

4558 - IC1
1 4.744
2 4.74
3 4.64
4 0
5 4.73
6 4.74
7 4.73
8 9.468


MN3007 - IC2
1 8.8
2 4.38
3 4.25
4 0
5 0
6 4.37
7 4.03
8 4.03


CD4047 - IC3
1 8.66
2 0.18 VAC, 0.07 VDC
3 7.15
4 8.8
5 8.8
6 8.8
7 0
8 0.72 VAC, 0.23 VDC
9 0
10 4.16 VAC, 4.377 VDC
11 4.17 VAC, 4.38 VDC
12 0
13 8.68
14 8.8

LM358 - IC4
1 3.73VAC, 9.0 Hz with rate all the way up
2 2.35
3 0.85 VAC
4 0
5 4.28
6 4.31
7 0.54 VAC
8 9.467

[freshmex18]

is Q2 base too high? connected thru resistors to pins 7 and 8, showing 6V9, it can't be higher than that.

circuit diagram?

Looks like you are correct.  Someone in the comments on Tagboard posted the voltages for a working unit and the base and emitter should be way lower.  How would I go about fixing that?

V+
9.468

2N5087 - Q1
C 0
B 3.07
E 3.7

2N5088 - Q2
C 9.468
B 3.93
E 3.355

2N5088 - Q3
C 9.468
B 9.425
E 8.8

4558 - IC1
1 4.744
2 4.74
3 4.64
4 0
5 4.73
6 4.74
7 4.73
8 9.468


MN3007 - IC2
1 8.8
2 4.38
3 4.25
4 0
5 0
6 4.37
7 4.03
8 4.03


CD4047 - IC3
1 8.66
2 0.18 VAC, 0.07 VDC
3 7.15
4 8.8
5 8.8
6 8.8
7 0
8 0.72 VAC, 0.23 VDC
9 0
10 4.16 VAC, 4.377 VDC
11 4.17 VAC, 4.38 VDC
12 0
13 8.68
14 8.8

LM358 - IC4
1 3.73VAC, 9.0 Hz with rate all the way up
2 2.35
3 0.85 VAC
4 0
5 4.28
6 4.31
7 0.54 VAC
8 9.467

[freshmex18]

Tested with an audio probe.  Signal goes into the 3rd pin of the MN3007 but no signal out.  Tried the chip from my Electric Mistress that I know works and same thing.

Ok, so if the BBD is a known-good device and the bias is tested, the next-most-obvious reason no sound is coming out is that the clock isn't working.
Have you got any way you can check the frequency on the 4047?

I have a multimeter with a Hz option but I cannot get consistent readings.  I touch the black lead to ground and it immediately reads 60 Hz before the red touches anything.   I touch the red to any pin and I get either a reading of 60 Hz or 0 Hz. I don't know if I am doing something wrong

[duck_arse]

why is that ponit F there? does it connect to something, or is it a test point?

Q2 5088
C 8.82
B 7.84
E 7.32
....

IC 2 MN3007
1 8.21
2 0
3 5.90
4 0
5 0
6 8.21
7 6.90
8 6.93

the circuit diagram shows us three resistors between the IC and the base. somehow, extra volts have appeared at the base. either wrong transistor type, transistor backwards, out-by-one type wiring error, bad cap, or something else.


it doesn't matter that/we all know that tagboard doesn't diagram properly, but that doesn't excuse building the circuit without a schematic, or posting a problem without also finding and posting the schematic. there's plenty of grumpy old fart-types here will just close the page if help asked w/ no schem provided. plenty.


you also neeed to trimm all those leads on the solder side, look for shorts and missed cuts.

[freshmex18]

why is that ponit F there? does it connect to something, or is it a test point?

Q2 5088
C 8.82
B 7.84
E 7.32
....

IC 2 MN3007
1 8.21
2 0
3 5.90
4 0
5 0
6 8.21
7 6.90
8 6.93

the circuit diagram shows us three resistors between the IC and the base. somehow, extra volts have appeared at the base. either wrong transistor type, transistor backwards, out-by-one type wiring error, bad cap, or something else.


it doesn't matter that/we all know that tagboard doesn't diagram properly, but that doesn't excuse building the circuit without a schematic, or posting a problem without also finding and posting the schematic. there's plenty of grumpy old fart-types here will just close the page if help asked w/ no schem provided. plenty.


you also neeed to trimm all those leads on the solder side, look for shorts and missed cuts.

Noted.  I will post with schematics from here on out

I think the F point is a test point?  There is also an A and a D point there as well.

I adjusted the trimmer to match the Q1 readings for the working unit.  For Q2, I re-knifed the resistor connections to IC2, checked connections, double checked, reflowed, etc.  Q2 now reads

C 8.9V
B 5.51V
E 4.95V

[antonis]

Q2 now reads
C 8.9V
B 5.51V
E 4.95V

You now have a very happy Sallen-Key 2nd order LPF Emitter follower..!! 

[freshmex18]

You now have a very happy Sallen-Key 2nd order LPF Emitter follower..!! 

That may be, but the circuit is still not working....

One problem fixed is still a victory though

[ElectricDruid]

You now have a very happy Sallen-Key 2nd order LPF Emitter follower..!! 

That may be, but the circuit is still not working....
One problem fixed is still a victory though

I agree.

However, Q2 is on the output side, so it's not likely to have sorted the problem out unless/until we get signal through the BBD. We've got audio going in at pin 3 of the MN3007, correct? And nothing at pins 7/8, or the test point F?

If you didn't manage to get any conclusive readings from the clock, it doesn't prove anything for sure, but it certainly doesn't rule out the clock not working being the problem.

I would test the clock by lifting one end of the 39K resistor to remove the LFO (and who knows, that alone might make it go) and then removing the diode from pin 2 to 3 and replacing it wih a pot. Not sure of the value.
That turns the 4047 into a simple astable and should be enough to get the thing running and test BBD.

[freshmex18]

I would test the clock by lifting one end of the 39K resistor to remove the LFO (and who knows, that alone might make it go) and then removing the diode from pin 2 to 3 and replacing it wih a pot. Not sure of the value.

Lifted the 39k and no change.  Removed the 4148 and replaced it with a A100k pot and bingo.  For the first 10% of the pot, pins 7 and 8 of the MN3007 had output.  Very low volume compared to pin 3 but it was there!

[ElectricDruid]

Lifted the 39k and no change.  Removed the 4148 and replaced it with a A100k pot and bingo.  For the first 10% of the pot, pins 7 and 8 of the MN3007 had output.  Very low volume compared to pin 3 but it was there!

Ok! Excellent! That's a good start. I hadn't had a chance to find out what the frequency out of the 4047 is supposed to be, but I had a dig in an old book I have and it suggests 0.23/RC as a guideline.
That'd give about 15KHz with 100K, and upwards from there, so 150KHz at 10K. I'm not sure exactly where MN3007 will top out when driven by a 4047 on its own, but you certainly won't be able to get down to 1K on the pot without losing the signal. That'd be 1.5MHz, and running a MN3007 that fast takes real work! I'd guess it gives up somewhere in the 200-300KHz range, but that's only a guess. If you've got signal coming through the delay line, you can tweak the bias trim to get that better dialled in and perhaps you can get a bit more level out of it. It shouldn't be too different from what goes in.

You should also take a moment to check the rest of the circuit, make sure those filters are working ok, and that final mixer with de-emphasis is doing what you expect.

Assuming all that seems to be ok, that basically means there's something up with the LFO that's dragging that clock chip off somewhere it doesn't want to go and stopping it oscillating.

[freshmex18]

Assuming all that seems to be ok, that basically means there's something up with the LFO that's dragging that clock chip off somewhere it doesn't want to go and stopping it oscillating.

Finally got a few free minutes to work on it and switching out the diode for a fresh one did the job!  Circuit works.  Kind of.

Not much happening for the first half of the depth mod.  And there is a noticable volume drop.

There is also a very loud ticking going on in the last 25% of the depth knob.  Might have to stick a buffer in there and see if that fixes things.  Someone in the tagboard post comments said they had a ticking problem and a Klon buffer cured that problem.  I tried it with a JHS Black Buffer in front and the ticking went away for all but the last bit of the depth knob.

So mostly fixed but there is still more going on