How to test mn3207 EMv2 circuit?

[Steve Blackdog]

Hi Folks

I have just built DrAlx's 18v electric mistress clone (schematic attached)


I can't get any flange effect. I have the bias on pin3 of mn3207 set to 5.2V, but it makes no difference if it is 1v higher or lower.

My question is about how to test for the circuit to trouble shoot it. Where should I first be able to see/hear any flange effect with a scope, or audio probe? 

By the way, I have reflowed all soldering and cleaned the board in case of shorts.  I have tried powering the board with a mt3608 dc-dc daughter board, and currently 2V 9v pp3 batteries in series.

Any other ideas gratefully received.

[DrAlx]

Was this from a PCB I sold, or did you do you own layout?
All the boards I have sold are from later revisions with a couple of extra parts to filter out supply noise when using a boost board as supply, though if you have no flange it is down to something else.

Do you have a scope or just a volt meter? Assuming you have only a meter,
the first step is use filter matrix mode (no sweep) with range pot at maximum, and take voltage measurements at all IC pins and post them here, or better yet, try and write them on the schematic.


FYI, the build docunent for the latest revision is here ...

https://1drv.ms/b/s!AvrH61utWEtEnSQgKV4JVc0pglmy?e=pmlmXx

and the revision history at the end of the document lists part value changes I made to get the sweep range and rate to match an original V2 EM.  Basically anything from Version 7 onwards has the same part values in the VCO and LFO.

[DrAlx]

The point marked test is the first point you would hear a flange effect.
If you have an audio probe, check the input pin (pin 3) of the 3207 to make sure you have audio going into the BBD, then pin 7 or 8 (the output) to see if you have audio out of the BBD.

[Steve Blackdog]

Hi Alex

Thanks for your speedy response. Yes, it is one I bought from you.  I was having trouble uploading anything other than a photo to this site! So I am working from the latest build guide.

I have an audio probe and I get audio in and out of mn3207 and also on the test point. I will test the voltages as suggested and report back!

Thanks again.

[Steve Blackdog]

Here's the annotated schematic. The battery power supply was only putting out 14.5 v, but this is not a factor as there was no flanger effect when the batteries were measured at 16.5v.

I have an oscilloscope, but I am not knowledgeable about using it.  My input was a signal generator set at 1kHz.

There's sound at the test point (and bbd output).

Does any of this point at the issue?

[DrAlx]

Voltages are OK. Audio out of the BBD is a good sign.  If it's a genuine BBD you will also find that bias too high or too low will not let any audio through. BBD OK means that the VCO and clock circuitry (LM311, CD4013, CD4050) are all ok too, since BBD will not let audio through without a clock. No flange suggests no clock sweep.

Do these 2 sets of measurements at pin 2 of the LM311.  That is the control voltage that determines the clock rate.
In filter matrix mode, the range pot sets that control voltage directly to a fixed value.
In sweep mode, the LFO circuitry varies the control voltage (it's a triangle wave). So...

1) In filter matrix mode, measure pin 2 voltage with range pot at maximum, and then again with range pot at minimum, and report the voltages here.
You should expect high voltage when range pot is at maximum, and low voltage when range pot is at minimum.

2) In sweep mode (i.e. not filter matrix), set range pot to maximum and rate pot at minimum (aim is to give a wide slow sweep) and try to measure minimum and maximum voltages at LM311pin 2.  It will vary so might be hard to do with a multimeter.  If you are not getting any variation in the voltage at all, it suggests the LFO circuitry (TL062 and parts around it) is not working. in that case, keep pots set to give wide slow sweep, and measure voltages at all 8 pins of the TL062 and post them here.  Note which voltages are varying (if any).  In particular, a  correctly working LFO will have pin1 of the TL062 jump between close to 12v and close to 0v around every 6 seconds or so.  If the pin 1 voltage is stuck (either high or low) it suggests a build error or bad part. I can advise better once I see the voltages.

[Steve Blackdog]

Thanks Alex

I am guessing builder error is more likely than bad part, but who knows.

LM311 pin 2 = 1.4v or thereabouts, whatever the settings.

TL062
1. = .65v
2=5
3=0.65
4=0
5=5
6 (min rate pot) = 10.5v
6 (max rate pot) = 4.9v
7=.65
8=10.9v

Any ideas? Should I disassemble part of the board?

[DrAlx]

 Can't answer yet (got to go somewhere). Will look into it later tonight.  Don't disassemble anything yet.
Are you saying LM311 pin 2 was not affected by range pot settings in either filter matrix mode of sweep mode ?

[DrAlx]

Pin 6 voltage (which is high) makes no sense. That pin is connected via the 2 capacitors to pin 7 (which is low) and via the rate pot to pin 1 (which is low). So that high voltage could come from only one place, and that is those two capacitors.
Those capacitors.must have been charged when you put them in the circuit.
So try this.

Power off the circuit.
Short out pin 6 to pin 7 of the TL062. That should discharge the capacitors.
Then power up the circuit again.

[DrAlx]

In a correctly working circuit, for TL062 the pin 6 will always measure same as pin 5 (regardless of range and rate pot settings).
The fact that you had the rate pot influencing the voltage there makes me wonder if there is some wiring error.

Do this. Completely remove the TL062 from the circuit.
The first thing to get correct is filter matrix mode (and that does not depend on the LFO circuit at all).
In that mode, the range pot directly sets the voltage at pin 2 of the LM311.
Look at the schematic and you will see that in that mode, the range pot is acting as a basic voltage divider.
So measure the voltages at the outer pins of the range pot, and at the middle pin of the range pot.
The middle pin of the range pot should have same voltage as pin 2 of the LM311.
If the middle pin of the range pot does not match pin 2 Lm311 voltage then you have a wiring error.

[Steve Blackdog]

There's definitely something wrong. With TL062 out, the voltages at range 1, 2 &3 all match pin 2 of LM 311, all around 1v.

I think I will leave it a few days and take another look with a fresh mind.

Cheers- Steve

[DrAlx]

Did you forget to run a wire from the middle pin of the sweep/filter matrix switch to pin 3 of the range pot ? See wiring diagram at very end of the build document. That would explain why the range pot was doing nothing.

Note that the PCB offers 2 holes for pin 3 of the Range pot (marked "Range3" in diagram at top of page 7 of build doc).  So you can use one of those Range3  holes for connecting to pin 3 of the range pot, and the other Range3 hole to run a wire to the middle pin of the sweep/filter matrix switch.

[Steve Blackdog]

BINGO!

I had wired the FM switch to the rate pot -duh!

I now have a great sounding Flanger.

Vast kudos to you Alex. Super happy 

[DrAlx]

Glad it worked out.