Merlin's Glassblower TH Custom, assembly help needed

[Matness]

I added the resistor, now the LED does light up.

When pedal is off audio passes through unaffected.
When pedal is on there is no output at all.

Polarity of all components (electrolytics, diodes) is correct according to the markings on the boards.  I just triple-checked.  (see attached photo of PCB from Musikding website)

Orientation of IC and Transistors is correct according to the photo on the instruction sheet.
https://diy.thcustom.com/?wpdmdl=3881

Yet still no output...

I've checked for solder points which might be close enough to arc, reflowed the joints which were questionable, brushed the surface to dislodge conductive debris, etc...

What else could it be? 

[jimilee]

Ok, we’re making progress. Were you able to reflow both sides of R4?

Audio probe is the next step.

Here is a really basic one.  If you have a 100n cap and extra wire, you can solder it to the out jack you have there already.

https://www.reddit.com/r/diypedals/comments/lqq3ku/diy_audio_probe_how_did_i_not_have_one_of_these/?utm_source=share&utm_medium=ios_app&utm_name=ioscss&utm_content=3&utm_term=1

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[Matness]

Ok, we’re making progress. Were you able to reflow both sides of R4?

Audio probe is the next step.

I reflowed both sides of R4 as per your suggestion, as well as many other joints even though they all look normal.   No change at all.   I tested continuity between all GND points and chassis (all 0.0 ohms), and between all 9V DC points (0.0 ohms).   Resistance between 9VDC and GND is 4.7k...  Does that seem normal?

I also tested all resistors (not for spec, just for continuity) none are open.  Tested all capacitors (in circuit) all normal values except that one of the 10uF reads as 60uF...  Probably a quirk of the circuit, and that shouldn't result in 'no output' even if the capacitor is defective.   

I tried testing the diode in circuit, couldn't get a reading from it - 0V in both directions...  Should I pull it out and test it?  Or is that unlikely to be the culprit?   If faulty I'd have to replace it with a 1N4007 which is the only silicon diode I have on hand.

I will build the audio probe as you suggested, into the output jack of the pedal.
I have a 100nF capacitor, so no problem there.
 
Is there any risk of damaging the circuit if I accidentally probe the wrong spot?
I'll set up a jig for audio probing (signal source and amplifier) later on this evening and report back.

[Matness]

Uploading schematic for convenience

[jimilee]

Hello. Na, don’t pull anything out of the board until we probe it, don’t want to lift any pads just yet.


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[Matness]

Did some initial probing, results are discouraging...
With pedal switched on (LED lit) I detect (unamplified) audio at the following points:

Main board:
"OUT"

Switch board:
"BI", JI" and three switch lugs (see photo)

No audio at the potentiometer.   No audio from any pin of the IC or transistors.
No amplified audio anywhere.

See attached photo for clarification - I've marked points where I can detect audio with a yellow circle.

Do I have the wires between the two PCBs reversed?

I've been assuming that:
"BI" on switch goes to "OUT" on PCB
and
"BO" on switch goes to "IN" on PCB

Maybe I have that backwards?

[jimilee]

Board in goes to the in of the circuit board and board out goes to the out of the circuit board.


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[Matness]

Thanks jimilee!

I'd just finished swapping the wires when your message came through.
The pedal now seems to function as intended, except that I have the potentiometer reversed.

I can not overstate how helpful you've been! Your guidance was hugely appreciated!
Without you pointing me in the right direction I'd still be lost!

The only other thing I'm wondering, is:  I have a collection of germanium transistors harvested from late 60s electronics which I've been saving with the intention to some day build some fuzz pedals.   To get advice on which transistors are most useful for this should I start a new thread?  If so, which sub-forum?  The "Beginner's Paradise" category, or elsewhere?

Thanks again!

[jimilee]

Thanks jimilee!

I'd just finished swapping the wires when your message came through.
The pedal now seems to function as intended, except that I have the potentiometer reversed.

I can not overstate how helpful you've been! Your guidance was hugely appreciated!
Without you pointing me in the right direction I'd still be lost!

The only other thing I'm wondering, is:  I have a collection of germanium transistors harvested from late 60s electronics which I've been saving with the intention to some day build some fuzz pedals.   To get advice on which transistors are most useful for this should I start a new thread?  If so, which sub-forum?  The "Beginner's Paradise" category, or elsewhere?

Thanks again!

Woohoo! Glad you got it up and going, enjoy!

Fuzz transistors are out of my wheel house. Start a new thread and see who has info.


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