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Green Bean Tone Knob Woes

Started by colemaj, January 29, 2013, 05:54:28 AM

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colemaj

Hi guys, this is my first non-kit build and my first bean build. It's also the first snag I've ran into! Below is some information in what will hopefully be a helpful format!

Pedal: Green Machine
Problem: Tone knob does nothing, neither does the bright switch. Other than that sounds great. Drive, Fat, and Volume all work. LED lights up, no hum.
Steps towards resolution: Quadruple checked wiring, parts placement/orientation and then checked all that over again. I tested the pot with dmm and it looks to be fine. I soldered it back in and noticed that if the power cord is plugged in, the pot shows only 8 ohms(may be lower... my DMM isn't the best). This short goes away with the power turned off or the IC removed. It appears the short is in the IC, but I don't know if this indicates a bad IC or problems elsewhere. I tested it before boxing it but I must have missed the tone knob not working. Unboxing is no problem, if that's needed to check stuff.

Alterations: I didn't use a battery so I bypassed that part of the wiring.

Any help would be greatly appreciated!

Pics here http://imgur.com/a/ejhmB#3


Measurements
Positive at power jack: 9.42V
Positive coming into board: 9.42V
Ground in at board: 0V
All wiring ground locations: 0V

IC Pin 1: 4.6V
IC Pin 2: 4.73V
IC Pin 3: 4.52V
IC Pin 4: 0V
IC Pin 5: 4.6V
IC Pin 6: 4.6V
IC Pin 7: 4.6V
IC Pin 8: 9.2V

Tone Pot
Lug 1: 4.6
Lug 3: 4.6
Reistance between Lug 1,3: 8 ohm
Resistance between Lug 2,3: Variable
Resistance between lug 1,2: Variable



oldhousescott

Your tone pot measurement in circuit with power applied is bogus -- actually it is showing that the opamp is doing its job. Your other voltage measurements all look righteous. Looking at your pics, there may be a few sketchy solder joints, but I don't see anything obvious. Would it be possible to post a clearer pic of the component side?

colemaj

#2
Thanks! I don't know a lot about opamps/electronics and I'm still kind of learning as I go. I got a new soldering iron too. One of those joints that looks bridged in the pic isn't... it just  had a lead leaning over. I clipped it just to make sure. Here's more component side that might help. http://imgur.com/a/qDvsF

edit: After double/triple checking everyhthing I suspect I might have been sent the wrong caps. The two tone caps (C6 and C7) say 223K on them. This makes them 22nF when I need 220nF, right?

fendman

Looks like you may have found your problem :) Hope you have, I am doing the same board, but I am doing a Clay Jones Overdrive on it which is just a couple of different components here and there...probs will sound  much the same as the Green bean.

colemaj


oldhousescott

I love it when a plan comes together! Good catch, and isn't it gratifying to suss it out yourself?