Pastel Preamp no output

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mkultra69

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Need some help on this one. Built the pastel preamp but not getting any output signal. Went through and checked every resistor, swapped IC's, and reflowed solder on a few points that looked a little sus. , but still nothing. Have an audio probe and have good strong signal up to R31, but after that it starts to get pretty weak and distorted. I do have a weak distorted signal at pin 1 and 7 of the IC, but nothing at Q8 or Q9.

I did have to make some resistor values as I didn't have any 120 or 27 ohm resistors so that's why R15 and R29 look a bit off. I also found some 39ks that measured 38.4ish for R20 and R7. Any help would be much appreciated. IMG_6355.jpg IMG_6356.jpg https://docs.pedalpcb.com/project/Pastel-PedalPCB.pdf
 
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If you have signal up to pin 1 of R31 (the pin that has continuity to the Master pot) then I would check the pot for resistance and continuity thru its range and see why it's not passing signal.

Also, see if your VREF (pin 3 of IC1) is shorted to something, like ground
 
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Thanks Ill check tonight when I get home. A bad pot would be nice, I really took my time with this one since there are so many components I didn't want to have to go through this lol. I did check the IC. 4.32v on pins 1, 2, 3, 5, 6 and 7. 1.2mv on pin 4 and 8.73v on pin 8
 
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I am really lost with this one. Checked the Master pot and it seem fine. There is a bit of an oddity with the "PRE" A10k pot. Between pin 1 and 3 I get 10k~ turned all the way to one direction but when I turn it the other way it drops to 5k. Thought that might be the issue so de-soldered it and checked it and it was fine. On the board i get 5k resistance between 1and 3 with no pot installed. Looking at the schematic shouldn't that just be going to ground? Maybe I just have a bad board idk.
 
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To clarify my understanding. You get good audio when probing up until the master pot, and after that it is weak?

Have you tried reflowing the pot pads? The middle leg looks like it's soldered with blu-tack and good intentions.
 
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szukalski said:
To clarify my understanding. You get good audio when probing up until the master pot, and after that it is weak?

Have you tried reflowing the pot pads? The middle leg looks like it's soldered with blu-tack and good intentions.
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Yes after the master pot the signal starts to get real bad and by the time it hits the IC its super low and what I can hear is really distorted. When I probe the output it is dead quiet like the signal is going to ground somewhere. I did reflow pretty much everything at this point, checked that leg with a meter and Im getting 2 ohms from the leg to the solder pad on the back of the board.
Erik S said:
That pin isn't folded under is it?

View attachment 102800
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Just double checked and it is fully inserted, just a bad angle on the pic.
 
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Quick update. Swapped out the 22nf for a 22pf cap and still nothing. I was able to audio trace down to pin 2 of R42 but nothing passes through that resistor. When I probe pin 1 its dead silence like I'm going straight to ground. I have no signal on either Q8 or Q9.
 
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Q8-C1.8v B2.38v E3v
Q9-C8.72v B4.62v E3.98v
I measured R43 with my meter and installed in the board it measures 2.7k so I pulled it out thinking maybe it’s bad and it measured the proper 82k. With no resistor in that spot at all it still measures 2.7k between pin 1 and 2 so not sure if that is something.
 
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mkultra69 said:
Q8-C1.8v B2.38v E3v
Q9-C8.72v B4.62v E3.98v
I measured R43 with my meter and installed in the board it measures 2.7k so I pulled it out thinking maybe it’s bad and it measured the proper 82k. With no resistor in that spot at all it still measures 2.7k between pin 1 and 2 so not sure if that is something.
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Na, when you measure them in the circuit, you’re measuring everything around it. You can just lift one leg, for future reference.

Go back and reflow all your solder joints in the same row as R44 and R45. The solder should flow through the board.
 
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Thanks everyone for the help and suggestions but Im going to have to shelf this one for a while. I just cant get this one to work. I have reflowed all solder joints insuring it flowed through the board. Rechecked every value, swapped out a cap that was not right (thanks Robert) pulled Q8 and Q9 and tested them to make sure they were still good. I'll order up a new board at some point and try again, hopefully I will be able to get a fresh board to work and I will be able to see where I went wrong. If it always worked the first time I wouldn't learn anything. :)
 
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