Effects Layouts EF120 - No output, Signal dying at Q1 SOLVED

[pangeadestructor]

This is the EF120 from Effects Layouts, clone of the DA120. I got it all populated and looking good, plugged it in and...nothing. After a visual inspection and reflowing some questionable joints, I tried the audio probe. The problem starts, as far as I can tell, at Q1. Signal going into the gate/center leg is strong, but when I touch the probe to the other two legs I get what sounds like the signal trying to get through but fizzling out instead. Like it's starving the signal somewhere in there.

Thought it might be a power issue but I went over the power section and it seems ok, I have voltage at pins 4/11 of IC 1 as well, and the LED lights up. I'm kinda stumped other than maybe a bad BS170. After Q1 I can hear the same weak, farty audio signal with zero sustain at D1, R3 and R4 and then it's pretty much gone. Any help is appreciated, sometimes I just need a fresh pair of eyes to ID the issue I've been staring at for hours.

Build doc: http://effectslayouts.com/wp-content/uploads/2022/11/EF120-build-doc.pdf

[duck_arse]

I have voltage

no sir, we need much more than "have voltage". measure all the voltages, post all those measures. all the transistors, all the IC's, all the supplies. please.

[Dormammu]

My advice is to apply the input signal (through the cap) bypassing the cascades one by one. So you will find out where the signal is lost.

[GibsonGM]

Welcome to the forum, Pangea

An easy to see pic of the actual schematic would be helpful (rather than a PDF...some ppl like myself have issues with them). Then we'll have a common image to refer to so we can send you on your way to do some fixing!     back of the PCB shots are good too, since a good % of problems will be found there.

[antonis]

An easy to see pic of the actual schematic would be helpful (rather than a PDF...some ppl like myself have issues with them).

Aye aye, Sir..

[Govmnt_Lacky]

C2 installed backwards

[antonis]

C2 installed backwards

Eagle eye..

(but that doesn't justify the above described circuit behavior..)

[Govmnt_Lacky]

C2 installed backwards

Eagle eye..

(but that doesn't justify the above described circuit behavior..)

Possibly but, fixing found mistakes may prove to change the discrepancy. Start with the easy stuff and proceed 

[pangeadestructor]

Thanks for all the replies so far, got some voltages to share.

IC1
1 8.62   5 -7.48
2 4.49   6 7.65
3 0      7 3.96
4 -3.42   8 8.62

IC2
4 8.62   11 -7.48

Q1  S 4.29 G 6.29 D 4.32

Q2  S 4.31 G 6.28 D 4.32

Q3  S 4.30 G 6.20 D 4.29

Q4  S 4.30 G 6.18 D 4.29

[pangeadestructor]

C2 installed backwards

Eagle eye..

(but that doesn't justify the above described circuit behavior..)

Possibly but, fixing found mistakes may prove to change the discrepancy. Start with the easy stuff and proceed 

See this is what I'm talking about when I mention a fresh set of eyes. I looked at that at least 10 times and thought "yup, looks good to me." Good looking out, thanks. I'll swap that out shortly and see what happens.

[pangeadestructor]

Corrected the C2 polarity, no change but it needed to be done anyway.

[antonis]

You must have a supply issue around IC2.. 

Check R30/R31 values/ratio or better check VR,,
(it should measure about 60% of VC..)

Q1 to Q3 are bottomed due to high Source voltage caused by high Gate voltage..
(they should be biased at S: 1/3VC and D: 2/3VC..)
As for Q4, you should be able to bias it (via 100k trimpot) at S: 1/4VC and D: 3/4VC..

[Dormammu]

C2 installed backwards

Eagle eye..

(but that doesn't justify the above described circuit behavior..)

Nope, C2 is installed correctly.
UPD: Oh, shi...  It on the board.  My bad. ¯\_(ツ)_/¯

But it should be taken into account that even the "wrong" polarity in such a connection will work.

[pangeadestructor]

You must have a supply issue around IC2.. 

Check R30/R31 values/ratio or better check VR,,
(it should measure about 60% of VC..)

Q1 to Q3 are bottomed due to high Source voltage caused by high Gate voltage..
(they should be biased at S: 1/3VC and D: 2/3VC..)
As for Q4, you should be able to bias it (via 100k trimpot) at S: 1/4VC and D: 3/4VC..

Looks like I may have used a wrong value at R30, based on the color code it looks like a 27k when it should be 62k. Gonna pop that out and replace it. R31 is the correct 100k.

[PRR]

> may have used a wrong value at R30, based on the color code it looks like a 27k when it should be 62k.

As shown by the voltage on Q1 Gate.

Anything called "Vref" should be reported. We don't ask for that enough.

[pangeadestructor]

I replaced R30, and I have output. Only tested it through my little practice box, but it sounds like I'm in business with this one.

Thank you so much for your help on this, I would have approached the issue all wrong without the assistance.

[Govmnt_Lacky]

I replaced R30, and I have output. Only tested it through my little practice box, but it sounds like I'm in business with this one.

Thank you so much for your help on this, I would have approached the issue all wrong without the assistance.

Good to hear.

Just remember, no matter how simple or complex the circuit... ALWAYS take a few minutes after populating the board to verify resistor values, cap values, cap orientation, IC orientation, etc.

[antonis]

¯\_(ツ)_/¯

Do I have your permission for copying that thumbnail..??

[PRR]

¯\_(ツ)_/¯

Do I have your permission for copying that thumbnail..??

The  ¯\_(ツ)_/¯  smilie is over a decade old.
https://www.google.com/search?q=%C2%AF%5C_%28%E3%83%84%29_%2F%C2%AF
https://en.wikipedia.org/wiki/Tsu_(kana)

[Dormammu]

¯\_(ツ)_/¯

Do I have your permission for copying that thumbnail..??

No doubt.