Author Topic: Doppleganger LFO1 not working  (Read 212 times)

trotel

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Doppleganger LFO1 not working
« on: August 27, 2017, 12:29:03 AM »
Hello great folks of Madbean!  I've been lurking awhile and with all the great knowledge on this forum, have built up several Madbean projects.  Thanks to you all, I've learned a TON over the last year from basic electronics, to enclosure design and finishes. 

Currently, I'm stumped with my Doppelgagner build and really hoping you guys can help me sort it out.  (this is the v2.1d board).

I've been trying to debug the problem through the usual means (recheck component values, reflow solder joints, check for bridges/shorts) but no luck.  I've also quadruple checked the wiring to the 3PDT switches as well as checked the switches themselves.  I'm using B2K for the Spans.

From looking at some prior posts such as this one (http://www.madbeanpedals.com/forum/index.php?topic=17032.15) I can see I have some voltage issues on IC1 (pins 5-9), but I can't find the root cause.  I've swapped out IC1 with another (known working) TL074CN but that did not help.   

Some other odd behavior that may be a clue is that when I first plug in the 9V, D9, D10 and the HF LED light up briefly, but then fade out.  If I short IC pins 4/5 or 5/6 they also light up.

Here are my voltages:

Source: 9.41V 
IC1 (TL074):
1-3: 4.33 
4: 8.66
5: 1.6
6: 1.56
7: 1.56
8: 1.6 
9: 1.6
10: 1.6
11: 0 
12: 4-4.8
13: 4.2-4.8 
14: 3.5-5.2

IC2 (TL072)
1: 3.7-3.9
2: 4.0-4.2
3: 4.2-4.7
4: 0 
5: 4.2-4.7 
6: 4.2-4.7
7: 4.2-4.7 
8: 8.66

IC3 (TL074)
1-3:4.1 
4: 8.1 
5: 4.1 
6: 4.2 
7: 4.1 
8: 4.1 
9: 4.2 
10: 4.1 
11: 0 
12: 4.1 
13: 4.6 
14: 4.5 

IC4 (TL072)
1: 4.1 
2: 4.1
3: 3.3 
4: 0 
5: 4.1 
6: 4.1 
7: 4.2 
8: 8.1 

Any input is greatly appreciated!
 
« Last Edit: August 27, 2017, 12:33:33 AM by trotel »

alanp

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Re: Doppleganger LFO1 not working
« Reply #1 on: August 27, 2017, 01:53:06 AM »
Flick us a photo of both sides?
"Hot water, good dentishtry and shoft lavatory paper."
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trotel

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Re: Doppleganger LFO1 not working
« Reply #2 on: August 27, 2017, 11:27:35 AM »
Flick us a photo of both sides?

Derp... scrub a dub dub with some lacquer thinner and a toothbrush then alcohol.  It's working fine now!

Amazing how much tiny crud comes off with a good cleaning.  I'm surprised I missed it after inspecting with my USB microscope.  Need to make sure to add "cleaning" to my list of debug steps when I get stuck. 

Back to building, and thanks again!

m-Kresol

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Re: Doppleganger LFO1 not working
« Reply #3 on: August 27, 2017, 01:12:29 PM »
good to hear you got it working, it's a fun pedal for sure. What was the problem in the end? was there a solder bridge underneath some flux residue you didn't see?
I build pedals to hide my lousy playing.

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trotel

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Re: Doppleganger LFO1 not working
« Reply #4 on: August 27, 2017, 01:44:54 PM »
Exactly, solder bridge underneath some flux residue I couldn't see.  I'm not 100% sure where it was but I suspect it was between R26 and R27.  After looking at the layout diagram again, this would make sense given the low voltages I was reading on IC1 pins 5-9.

LaceSensor

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Re: Doppleganger LFO1 not working
« Reply #5 on: August 28, 2017, 01:26:07 PM »
Glad you got it working

Touch wood Ive not had anyone fail with this board

trotel

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Re: Doppleganger LFO1 not working
« Reply #6 on: August 28, 2017, 02:39:44 PM »
Thanks- Great to feel the strong support around here!