EA tremolo ROG: clean sound, led flashing but no tremolo

[Diyfr]

1.What does it do, not do, and sound like?: clean sound, led flashing according to the rate, but no tremolo sound (more explanation above)
2.Name of the circuit = ROG EA tremolo
3.Source of the circuit (URL of schematic or project) = Run Off Groove (see the schematic above)
4.Any modifications to the circuit?  No
5.Any parts substitutions?  No
6.Positive ground to negative ground conversion?  N
7. I use a power supply


Q1 (BS170)
D = 5.04 V
G = 1.73 V
S = 1.30V

Q2 (J201) 0 V seems logic according to the other EA topics
D = 0 V
S =0 V
G = 0 V

Q3 (2N5088)
C = about 3.5 V
B =0.58 V
E = 0 V


What it does and does not do how it works:
Yesterday I built this tremolo for a friend according to the ROG schematic, but it don't work.

I've got a clean sound. The volume pot works. The led is flashing according to the rate ... but no tremolo.

With an audio probe I've got a tremolo on the depth pot (pin 3), and the depth pot works.
If I put the audio probe after the 120K resistor, I can hear some pulses, but not the tremolo and what I play.
If I put the audii probe after the 0.47uF, I hear the same.
I do another test: I added after the depth pot (pin 3) another 120K and 0.47uF, and I didn't solder the "output" of the 0.47uF. When I put the audio probe on the "output" of the 0.47uF, I can hear the tremolo.

The problem seems to come from the Q3 section. I checked all many times, and didn't find the problem.

Do you have some advices ?

[Mark Hammer]

Check your pinouts on the J201.  An LFO applied to the wrong pin of the J201 still won't get you a systematic change in drain-source resistance.

[Diyfr]

Thanks for your reply.
I forgot to say that I always tried to invert the J201, and try another one, but it changed nothing.

I have checked the resistors with multimeter before building ... I will try another 1uF caps and see what happens.

[Mark Hammer]

To verify that everything except for the FET on the audio side is working properly, remove the J201 and simply connect a 10k-100k pot between the 22uf cap and ground.  Now vary the resistance of the pot (any two adjacent lugs will do).  You should hear a fluctuation in volume as you twidle the pot.  If you do, then there is nothing wrong with the audio path. 

Now, stick your meter's probe at the wiper of the Depth pot and measure the voltage there, with the frequency set to a moderate speed.  It should fluctuate.

If both those things check out then the weak link is your JFET.

[Diyfr]

test 1:
I use a 50KB. I heard a fluctuation but only at the end of the curse.

test 2:
you're right. V goes to -0.4 to 0.3 V.

So I will check around Q2, and try all the J201 I have in stock.

Thanks agan for your help !