SOLVED Softii - first build... no sound 🙃

[Petethefuzz]

Hi guys. Total n00b here. Just finished my first build. Maybe I took on to much, but I fell in love with the SFT so I wanted a clone. With help online/facebook I have tested that the switch works (multimeter buzz test). LED works. I’m very new
to electronics/circuits and even the multimeter. I have seen this kit in the forum - has anyone had the same issue? Doesn’t work out of the enclosure either, so it doesn’t appear to be pots making a short or something like that. I had to wire one of the transistors cause the socket
Was broken. I bought it as a kid from musikding.de

If you would be so kind to give me instructions on what and how to test, maybe with the multimeter, I’d really appreciate it. Please feel free to address me as a total beginner. If you feel like you are writing to a toddler your probably doing great

 

[Chuck D. Bones]

Did new reading. This time powering the pedal by battery.
Q1 1,28
Q2 9,3
Q3 0,81
Q4 5,95
Q5 0,84 (Stable)
Q6 5,43

Does this point towards a problem with Q2 or maybe components around it?

Yes.

Either there is a short between Q2 source and drain, or the connection between Q1 & Q2 is broken.
With power on, measure the voltage on Q1-D.
With power off, measure the resistance between Q2-S and Q1-D (should be 10K).

Report your findings.

Look carefully under the GAIN pot. It's hard to tell from the photo, but there might be a short there:

 

[Petethefuzz]

Cool I’ll try to measure that.This datasheet seems to apply right?
So leg:

1 Drain
2 Source
3 Gate

When you say “power on” does that also mean not bypassed? Or as that not of any importance?

 

[zgrav]

power on/off just refers to whether you have plugged in the jack.

 

[Petethefuzz]

power on/off just refers to whether you have plugged in the jack.

That makes no sense to me sorry... you don’t mean 9V power?

 

[zgrav]

yes. sorry for not being clear. I was referring to the power jack not the audio cables.

 

[Chuck D. Bones]

As further clarification, in-circuit resistance measurements can only be made with the circuit unpowered.

 

[fig]

As further clarification, in-circuit resistance measurements can only be made with the circuit unpowered.

do pots count as in-circuit resistance?

 

[Chuck D. Bones]

Anything that's wired into the circuit counts as "in-circuit."

 

[Petethefuzz]

Yes.

Either there is a short between Q2 source and drain, or the connection between Q1 & Q2 is broken.
With power on, measure the voltage on Q1-D.
With power off, measure the resistance between Q2-S and Q1-D (should be 10K).

Report your findings.

Look carefully under the GAIN pot. It's hard to tell from the photo, but there might be a short there:
View attachment 10129

ok - here are my findings:


“With power on, measure the voltage on Q1-D. “

= 8V

“With power off, measure the resistance between Q2-S and Q1-D (should be 10K).”

= 5,54 ohms

- I also checked for a short under the pots but didn’t find any

 

[Chuck D. Bones]

That 10K resistor is shorted out. More visual inspection. is required.

One more thing, measure the voltage on Q2-G (with power on). The results will depend on you DMM's input resistance.

 

[sofaking74]

 

[PJS]

Not sure about the joint at the very bottom of that photo either

 

[Petethefuzz]

That 10K resistor is shorted out. More visual inspection. is required.

One more thing, measure the voltage on Q2-G (with power on). The results will depend on you DMM's input resistance.

Do you mean R7? I’ll check it out. Think its time I see if I can desolder the pots though it seems tricky. Q2 gate shows no voltage at all. Power is on.

 

[Chuck D. Bones]

We're getting closer to the problem.

First, with power off, measure the resistance from Q2-G to ground.

Next, with power on, measure the voltage on each side of R5 w.r.t. ground. One side should be +9V and the other side should be between +3V and +4.3V, depending on the input resistance of your DMM. Which DMM are you using?

 

[Petethefuzz]

R5 measures 4,4V and 9,28V. I couldn’t get a reading on resistance of Q2 G (3. leg) though...

This is my DMM:

 

[Chuck D. Bones]

That's a good meter. Input impedance is 10MΩ.

Your R5 measurement tells me that the R5/R6 voltage divider is working. When you say you can't get a resistance reading on Q2-G, I think you mean the reading is >10MΩ. Just to be clear, you measured this with Q2 still installed on the board, correct?
All of this points to a broken pad at Q2-G or a broken trace between R5 and Q2-G. More visual inspection is needed. Look right around here:


If the trace or pad are damaged, it's easily repaired.

You're in the UK, right? That explains why it takes each one of us the better part of a day to respond.

 

[Petethefuzz]

That's a good meter. Input impedance is 10MΩ.

Your R5 measurement tells me that the R5/R6 voltage divider is working. When you say you can't get a resistance reading on Q2-G, I think you mean the reading is >10MΩ. Just to be clear, you measured this with Q2 still installed on the board, correct?
All of this points to a broken pad at Q2-G or a broken trace between R5 and Q2-G. More visual inspection is needed. Look right around here:
View attachment 10267

If the trace or pad are damaged, it's easily repaired.

You're in the UK, right? That explains why it takes each one of us the better part of a day to respond.

Hi Chuck! I’m from Denmark, so assuming your from the other side of the great pond, I’m even +1 hour from London time so it’s even worse

Regarding reading resistance from q2g I think your right... so I couldn’t measure it because the value was to low? I’m (obviously) no expert so I tried all relevant setting with no luck in the DMM.

The marking on the picture looks a bit rough. Haven’t had time to clean it but I’ll get to it. How would you go about repairing it if say the trace is broken?

- again I can’t thank you enough for all the help! I’m learning so much and it helps against the disappointment of the damn thing not working

 

[zgrav]

You could not measure the resistance with your DMM if there was no connection between those two points, or if they were connected but the resistance between them was greater than 10Meg.

You can repair a broken trace by using a small wire to connect the points that are supposed to be connected by the broken trace.

 

[Chuck D. Bones]

Before you attempt repair, let's confirm that the trace is in fact broken. You might need some magnification to see the break.

I'm in Los Angeles so you're 9hrs ahead of me. I guessed the UK because that's where your meter is sold. At least that's where eBay vendors are located.

 

[Petethefuzz]

Before you attempt repair, let's confirm that the trace is in fact broken. You might need some magnification to see the break.

I'm in Los Angeles so you're 9hrs ahead of me. I guessed the UK because that's where your meter is sold. At least that's where eBay vendors are located.

There appears to be something going on but I don’t no if it’s enough to cut the trace. Something has happened to one side of the trace though...