Debugging a Neovibe

[Chrissie]

Hey all,

I'm trying to get my recently build neovibe working.
My neovibe is made on a pcb wiht the ggg layout.
Current problems: In the LFOcircuit the lamp won't light up and there's fuzzy distortion in the audio part of the circuit.

I already scanned the board several times for tracecuts, and wrong components.
Below are the transistor voltages (All  2n3904's).

On first sight all the voltages are rather ok? except the collector voltage on q3 seems way to low...

Any  suggestions?

Q1
C=3,1
B=2,6
E=2,0

Q2
C=8,3
B=3,1
E=2,7

Q3
C=7,6
B=8,3
E=7,6

Q4
C=14,9
B=5,0
E=4,5

Q5
C=10,9
B=4,5
E=3,9

Q6
C=14,9
B=4,8
E=4,3

Q7
C=11,3
B=4,3
E=3,6

Q8
C=14,9
B=4,8
E=4,3

Q9
C=11,3
B=4,3
E=3,6

Q10
C=14,9
B=5,8
E=5,3

Q11
C=21,5
B=8,6-11,5
E=9,8-13,8

Q12
C=21,5
B=9,9-14,0
E=9,2-13,3

Q13
C=20,9
B=4,4-5,5
E=4,0-4,5

[R.G.]

Q1
C=3,1
B=2,6
E=2,0

Q2
C=8,3
B=3,1
E=2,7

Q3
C=7,6
B=8,3
E=7,6

There is a huge problem here. You're correct, the collector voltage on Q2 is low. But more interestingly, both collector and emitter are at the same voltage. It's impossible to tell from the voltages whether collector and emitter are shorted together, or whether the base is pulled so high that the transistor is saturated. I'm guessing the transistor is saturated. The collector on Q2 should not be so high. I'm guessing a soldering problem or similar in the whole Q1/Q2/Q3 area. Sorry - but if it was all the right parts and had all the right connections made and no extra connections made, it would be working. Are the transistors oriented the right way round?

Q13
C=20,9
B=4,4-5,5
E=4,0-4,5

The emitter is way too high. Either you have a wrong part value for the emitter resistor and trimmer pot, or there's an open circuit (=bad soldering) on one of them.

[Chrissie]

Q1
C=3,1
B=2,6
E=2,0

Q2
C=8,3
B=3,1
E=2,7

Q3
C=7,6
B=8,3
E=7,6

There is a huge problem here. You're correct, the collector voltage on Q2 is low. But more interestingly, both collector and emitter are at the same voltage. It's impossible to tell from the voltages whether collector and emitter are shorted together, or whether the base is pulled so high that the transistor is saturated. I'm guessing the transistor is saturated. The collector on Q2 should not be so high. I'm guessing a soldering problem or similar in the whole Q1/Q2/Q3 area. Sorry - but if it was all the right parts and had all the right connections made and no extra connections made, it would be working. Are the transistors oriented the right way round?

I think I found the problem: a cold solder spot @ R6

the new voltages :

Q1
C= 2,2
B= 1,4
E= 0,9

Q2
C= 4,1
B= 2,2
E= 1,5

Q3
C= 11,3
B= 4,1
E= 3,4

I think they are way more acceptable. 

Q13
C=20,9
B=4,4-5,5
E=4,0-4,5

The emitter is way too high. Either you have a wrong part value for the emitter resistor and trimmer pot, or there's an open circuit (=bad soldering) on one of them.

This  problem was caused by a broken trimpot, although it was brand new! 
The LFO-circuit seems to work correctly and the speed & depth controls do exactly what they are supposed to do...

IT WORKS!
THX R.G.!
I now have a wonderful wobbly vibe.

Unfortunately one little problem did occur: a loud 50hz hum.
When probing the circuit, I found that the hum only appears at the end of the circuit, where the mixing resistors are placed.
Is it because my vibe isn't in an enclosure yet?

[R.G.]

I think I found the problem: a cold solder spot @ R6
...
IT WORKS!

Good work. It had to be something like that.

Unfortunately one little problem did occur: a loud 50hz hum.
When probing the circuit, I found that the hum only appears at the end of the circuit, where the mixing resistors are placed.
Is it because my vibe isn't in an enclosure yet?

Could be. How are you powering it?

[Chrissie]

Unfortunately one little problem did occur: a loud 50hz hum.
When probing the circuit, I found that the hum only appears at the end of the circuit, where the mixing resistors are placed.
Is it because my vibe isn't in an enclosure yet?

Could be. How are you powering it?

I'm using 16,5V AC adapter from my Presonus firepod.
The hum also occurs when using an 18V DC power supply from an old laptop...

I also want to mention that the power Jack is isolated from the rest of the circuit.

[Chrissie]

Today I did put my neovibe in its enclosure and the hum is gone.   

@ R.G.:  Hereby I'd like to extend you a sincere thank you for your continuous efforts helping all those DIYers finishing their neovibes. THX!