Noise gate not working...

[FredG]

Hello

I have a problem with a noise gate kit I bought, here it is :

Name of the circuit = Das Noisegate

Source of the circuit
https://www.musikding.de/docs/musikding/noisegate/ng1_schalt.pdf

Modifications : no footswitch (always on)

Problem =
It worked briefly at the beginning, and when I boxed it, it didn't.
I have a significant volume drop and the potentiometre does nothing.
I unboxed it, still doesn't work.
I desolder and resolder all the wires to jacks and pot. Still the same problem.

Here are the numbers :

Circuit voltage out : 9,1
Circuit ground out : 0,0

T1
C = 9,1
B = 2,7
E = 3,26

T2
D= 4,2
S= 4,2
G= 3,36

T3
C = 3,36
B = 0,37
E = 0,0

IC1
P1 = 8,45
P2 = 4,41
P3 = 0,76
P4 = 0,0
P5 = 3,1
P6 = 4,64
P7 = 4,64
P8 = 9,1

D1
A = 0,0
K = 0,0

ZD1
A = 0,0
K = 4,21

Elec. Cap 1
+  9,1
0,0

Elec. Cap 2
+  4,26
0,0

Elec. Cap 5
+  4,4
0,0

Elec. Cap 6
+  3,24
4,26

Elec. Cap 10
+  3,4
0,0

Elec. Cap 12
+  4,64
0,0

Pot A500k (turned off)
1 = 4,16
2 = 0,78
3 = 0,0

Thank you in advance for all the help.
Fred

[Slowpoke101]

The most likely problem is that the voltage on pin 3 of the IC is far too low. Which then helps make the voltage on pin 1 far too high. Check R6 (1K ) and make sure that it is actually 1K and that it is soldered correctly. Then check the Threshold pot P1 for loose solder lugs and measure the voltages on each of its solder lugs - all should read close to 4.5V

Let us know what you find.

Edit: I now see that you did measure the voltages on the Threshold pot. The pot is either faulty or you have a short circuit to ground (0V ) on pin 3. Remove the wire going to pin 3 of the pot and measure the voltages on its pins again (even though pin 3 is not connected anywhere ). If they all measure about 4.5V then the pot is probably good and you need to check for loose strands of wire or solder splashes where the pin 3 wire connects to the board and around C4.

[FredG]

thank you very much Slowpoke101.

I checked all the value of resistor, they are all ok, no mistake there.
I checked all the solders, they all look nice and shiny.
I passed a blade all around them just in case, and cleaned everything with kontakt60.

The pot seems to be the problem here.
No bad solder or anything. I desoldered tip 3. But I have constant changing numbers on tip 2 and 3 (from 0 to 3,2V).
I opened it, passed a blade between the tips, clean it carefully with Kontakt60. It stabilized at
tip 1 = 4,2
tip 2 = 2,4
tip 3 = 2,4

Then I resolder tip 3 to the board and I have now :
tip 1 = 4,2
tip 2 = 1,43
tip 3 = 0

The IC's voltage also change a little bit :
1 = 5,08
2 = 4,40
3 = 1,40
4 = 0
5 = 3,10
6 = 4,64
7 = 4,64
8 = 9,11

[Slowpoke101]

It does look as if the Threshold pot is faulty so unless you have another one to substitute it with I suggest another test.

With no power applied to the circuit set you multimeter to a high ohm resistance test. Isolate tip 3 again and set the pot to midway. If you have the IC in a socket take it out but don't worry about doing so if it is not socketed. Now place one probe of the multimeter onto tip 2 and then the other probe to tip 1 - note the reading on the multimeter. Now take the probe that you tested tip 1 with and place it on tip 3. Check the multimeter's reading - it should be close to the previous reading. Now test between tip 1 and tip 3 - you should read about 500K.

Let us know how you go.

[FredG]

Yes, the pot is dead.
The screen of my multimetre stays blank, no mater where I put the tips.
I opened the pot to check directly on various places of the tape, and 1/3 of it was not responding at all.
I just have to wait for a new one now... 

Thank you again for your help Slowpoke, really appreciate !!