Need help with my DIY pedal (Tube screamer)

[00Psiho00]

Hello guys,

I tried to make my own Tube screamer clone from https://www.musikding.de/The-Screamer-Overdrive-kit and I hit a dead end!

When I put everything together the guitar works in bypass mode normally but when I engage the pedal there is no more sound and the overdrive doesn't work!
Now I checked the the placement of the parts on the PCB and everything is as it should be and turned the right way. I checked the IC with the multimeter and all the pins are ok. I also checked the base, emitter and collector on the transistors and they are fine too.
The measured voltage reading on the 3 transparent diodes is 0.574V and 0.622V on the black one. That should be also fine I think, but when I measure it the other way around I get 1.2V on the 3 diodes and 2V on the larger black one. Is that normal? Doesn't the diode let current only one way? I checked the PCB with continuity mode on the multimeter and everything was ok.

I cleaned the PCB with alcohol and scrapped between the solder joints to remove a possible solder bridge.

When I test it I connect all the ground wires (-) together (9V input, PCB, input and output jack), the positive red (9V+) from the PCB to the positive on the 9V input, the yellow input from the PCB to the input jack and blue wire to the output jack. I checked that the signal and ground connections on the jacks were not reversed.

The picture of my PCB:





Is there something else I need to check, what could be the issue here?
Any help is very much appreciated! 

[Mark Hammer]

I'm not sure what you mean by "the other way around", but the series combination of D2+D3 is supposed to produce a forward voltage of around 1.2V.  D1 has a forward voltage of around 500-600mv on its own.  The use of a 2+1 diode complement is intended to produce asymmetrical clipping, as found in the Boss SD-1.

The 1N4001 diode is intended to provide protection against use of the "wrong" polarity supply voltage, whether via battery or external supply.  It will pass current to ground if it receives a negative voltage above around 550-600mv.  The chip will still get 550-600mv, but that's not enough to fry it.

The slightly melted plastic cap beside the three diodes doesn't look especially healthy, but that may be simply cosmetic and not critical.

Plug your guitar in, apply power to the circuit, and set your meter to measure AC voltage in a lower range (e.g., less than 2 or 20V).  Strum the guitar and see if you get a corresponding reading at the junction of C1 and R2.  If you do then you know the guitar is making an appropriate connection to the board.  Take a similar sort of reading at the emitter of T1, and after C2.  Again, you should get something in the range of 100mv AC or less, when you strum.  Take a reading at pin 1, varying the gain control.  You should get something in the range of a half-volt or a little more with the gain maxed.

And so on.  The strategy is to take AC-voltage measurements where you expect to see changes corresponding to both the presence of a signal, and the amplification of the signal.  The point where you stop seeing such corresponding readings is clearly where the problem lies.  For instance, if you don't get a suitable reading at the T1 emitter, maybe you've installed T1 the wrong way around.  And so on.

[00Psiho00]

Thank you for the quick reply. I will measure everything as you described tomorrow and try to find the problem that way.
The caps is a little bit melted from the soldering iron but it shouldn't be damaged.

[duck_arse]

00Psiho00 - can we see some photos of the copper side of your board? have you any isolation/insulation between the pot bodies and the solders?

also, welcome to the forum.

[Marcos - Munky]

Are those parts really soldered. Looks like you used too less solder on them.

[EBK]

Reading this, I couldn't help but think of a problem I had once (maybe even more than once).  I powered up a perfectly wired circuit with reasonable voltage measurements and got a clean output on bypass but nothing when the effect was engaged.  Why?  I had plugged my guitar into the output jack and my amp into the input jack.  Just thought this was worth mentioning.   

[deadastronaut]

c7?

[EBK]

c7?

Intentionally empty:
http://diy.musikding.de/wp-content/uploads/2013/06/screamerV2_schalt.pdf

[00Psiho00]

This is the other side of the PCB








This was my second time soldering so it's not really perfect 

I double checked when plugging in the guitar, so I definitely didn't mix up Input and Output

[Kevin Mitchell]

Are you using a stomp switch? How do those connections look?

When in doubt... audio probe. Trace the signal from the input and find where it's disappearing.

If you don't have a chord to sacrifice just desolder the output jack (not the ground connection) and use that to poke around the board and find what's going on with your guitar signal.

Your soldering could be worse. If it helps  you feel any better - the placement of the parts look okay so as a noob you've got me beat.

[Marcos - Munky]

To me, still looks lack of more solder. Are you sure these parts are making contact on both sides of the board?

[00Psiho00]

I will try the audio probe method too over the weekend.
Lack of solder? Hmmm you know what, I could actually desolder everything and start over, maybe that's the best thing to do.

[Kevin Mitchell]

I could actually desolder everything and start over, maybe that's the best thing to do.

Hold up now. That's a good way to ruin your PCB.

Don't do that. Retouch your solder joints and apply more where it looks to be needed.

That comment about the solder making contact with both sides was a bit silly IMO. The board looks to be through-hole plated so that shouldn't be a concern unless it's a faulty board.

[Marcos - Munky]

Not all boards are through-hole plated, and from the pics I can't see if this one is. That's why I said about lack of solder. But like Kevin saidjust add a touch of solder where it looks it's lacking. Desolder everything is something that can ruin a board, even for the most soldering experienced person.

[thermionix]

The IC is fake.

[EBK]

The IC is fake.

No matter how many times you swoop in with this always excellent (I'm pretty sure you're always right, anyway) answer, I'm somehow always surprised.

It reminds me of:
"Nobody expects the Spanish Inquisition!" 

Well, that's my quota for Monty Python references for the day.

Good catch (you are sure, right? I never manage to learn the telltale signs)!

[thermionix]

I went through my stash of old and recent TI RC4558Ps, and online pics from reputable dealers and such, and they are all screen printed.  Or whatever the process, printed with ink, not a 3D stamping.  I actually can't find another on google images that matches OP's.

It might be a working dual opamp of some sort, maybe even a 4558, but not a TI as far as I can tell.  And the pedal doesn't work, so....

[00Psiho00]

The pedal finally works! 

The issue was a so small solder bridge somewhere on the PCB that I didn't see it before. I cleaned the PCB after the solder job 2 times with alcohol and thought it was ok.
So today I prepared the multimeter and an audio probe cable for testing but decided to clean it with a small brush once more and when I connected everything it worked perfectly!

I would like to thank everybody that helped out, thank you very much!
And I promise to not build any more pedals so that I don't have to bother you again 

[italianguy63]

To me looks like the solder contacts may be the culprit.  Based on how they look, I think your solder gun is too cold.

I would take 15 minutes and "refloat" those contacts... adding solder especially where you see air gaps.

You may need a higher wattage soldering iron. 

Anyway.  My .02.  Good luck!  Peeps here don't mind helping.

MC

[deadastronaut]

And I promise to not build any more pedals so that I don't have to bother you again 

no chance, your hooked now...

glad you got it sorted....