Debugging Brutalist Jr. pedal - No Signal when on

[dnox]

Hi everyone. I am a noob to the world of pedal building but it's something I've really enjoyed, from soldering components to designing the enclosure graphics. I completed my first build, a Brutalist Jr. from God City Instruments. I followed the detailed instructions on the site and put it together from a kit. No mods or substitutes that I am aware of. Got everything wired up and ready to go, pretty confident in my soldering and wiring (i know, I know  ), and it didn't work. The signal is there in bypass, but when I engage the effect the LED lights up but the signal is gone completely. Nothing.

So I reflowed all my joints, checked the wiring, and did a general visual inspection. I checked the switch and pots and I believe they are working based on measuring with a multimeter. Did connectivity tests to the best of my knowledge. Still Nothing.

So know I've taken IC and Diode measurements and I'm hoping someone can help me understand what they mean. Here are the measurements:

Battery Voltage = 8.80V

D1
A = 3.82
K = 4.03

D2
A = 4.02
K = 3.82

IC1
P1 = 4.25
P2 = .43
P3 = 0
P4 = 0
P5 = .4
P6 = 4.13
P7 = 4.25
P8 = 8.47

IC2
P1 = 4.25
P2 = 4.25
P3 = .2
P4 = 0
P5 = .4
P6 = .02
P7 = 4.25
P8 = 8.43

https://www.godcityinstruments.com/collections/diy-pcbs/products/brutalist-jr-distortion










Thank you so much in advance!
-Mike D.

[antonis]

Hi & Welcome.. 

First of all, check VA voltage..
It should be about: (your supply voltage minus 250-300mV) / 2

Start by checking R18 value (10R instead of 10k, perhaps..)
If both R17 & R18 are of the same value, check C16 for some kind of short..
(desolder and lift one cap leg..)

P.S.
R17 (the one hidden by C14 box cap) lower leg & pad seems like cold joint..
(in such a case, R17 10k value is reflected as a much higher one..)

[dnox]

I will check out your suggestions, thank you!

[dnox]

Hi Antonis,

Again thanks for taking a look. When you say measure the VA voltage, is that just checking those ICs' P5? If so they are still both measuring .4V. I assume this is the issue and it should be measuring closer to 4.25V? Apologies, this is the first time I've done anything like this, so reading the schematic has been a learning process.

R17 and R18 are both 10k. One thing I didn't mention was a mod I initially made that was suggested by the maker of the PCB. It was replacing R17, R18, and C16 with a TO-92 version of a TLE2426 rail splitter. It had the same problem then: signal when bypassed, no effect when engaged. So since I didn't really understand that mod, I thought I would change it to exactly how the build doc originally described and hope for the best. It's still not working so I would think that C-16 would not be the culprit?? But when I have time I will test that for a short.

Could there be another explanation that P5 is reading .4V?

Thank you!

[PRR]

"VA" comes from R17, R18, C16. What do they have for voltage? We expect about 8V, darn near Zero, and a half-way voltage. But an open or short almost anywhere will foul things up.

[antonis]

No need for apologies, Mike..
(schematics are a nasty way for designers to avenge unversed people..)

VA (which is about half of the power supply voltage) is formed in the junction of the two 10k resistors (R17 & R18) and is used for non-inverting inputs bias (pins 3 & 5 of both ICs 1 & 2)..
Taking into account that op-amps inputs draw no current, there shouldn't be any voltage drop, despite the value of biasing resistors..
So, "something" severely loads down VA, which might be either a C16 short or any of pins 3 and/or 5 of IC1 and/or IC2..