# Duo Phase LFO B Constant LED



## chongmagic (Nov 14, 2019)

I am putting together my second Duo Phase, first one worked great, sold it and wanted another. 

LFO A works fine and if I toggle to sweep switch both will work fine. I did sub the B25Ks for A25Ks, but I doubt that is the issue. Looking at the schematic it might be one of my TL072s is bad. I did replace the 4401 transistor just out of curiosity and it still stays constant with the LED if I toggle the sweep switch, the sync switch seems to just make the LED brighter on side B. 

I am still not the greatest with reading schematics, but it looks like if one of the TL072s is bad it would be, IC6B or IC5B.


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## chongmagic (Nov 14, 2019)

Also the voltages for the tl072s should be the same on each side since it is a mirror image right?


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## JetFixxxer (Nov 14, 2019)

My Duo Phase II LED was constant because I had the wrong resistor value.  Might want to check that if you haven't already done so.


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## chongmagic (Nov 14, 2019)

JetFixxxer said:


> My Duo Phase II LED was constant because I had the wrong resistor value.  Might want to check that if you haven't already done so.



I will double check, I always measure the resistor before I put it into place, but you never know when there are so many on this board.


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## Chuck D. Bones (Nov 14, 2019)

chongmagic said:


> Also the voltages for the tl072s should be the same on each side since it is a mirror image right?


Yes.  
Visual inspection.


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## chongmagic (Nov 14, 2019)

Here's a pic of the board as is, just in case I may be missing something.









						New item by Jonathan Freeman
					






					photos.app.goo.gl


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## chongmagic (Nov 14, 2019)

If I touch pin 3 of IC6B with a probe it starts flashing. Also R32B and R36B. Is that indicative of a short?


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## Chuck D. Bones (Nov 15, 2019)

I think it's indicative of a bad connection.  Is the probe connected to anything?


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## chongmagic (Nov 15, 2019)

No just the positive probe, not connected to anything but the MMD. Also if I pick up a washer and just touch one leg of a resistor the same thing. I reflowed the entire side, and the issue remains. But yeah I concur that there is a bad connection somewhere.


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## Chuck D. Bones (Nov 15, 2019)

It's possible that R32B or R36B aren't the values that are marked or there is a bad connection to them.  Try this: remove IC6B.  Set the SWEEP switch to A.  Measure resistance from IC6B-1 to IC6B-3, should be 68K.  Measure resistance from IC6B-7 to IC6B-3, should be 47K.


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## chongmagic (Nov 15, 2019)

The resistance is correct


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## chongmagic (Nov 15, 2019)

You know there was some solder mask off around IC5A when I got the board, I wonder if that could be the culprit.


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## chongmagic (Nov 15, 2019)

chongmagic said:


> You know there was some solder mask off around IC7A when I got the board, I wonder if that could be the culprit.


Cause I'm getting no output on side A and an audio probe at pin 5 of IC5A stops there, which is the IC I should have mentioned above.


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## Chuck D. Bones (Nov 15, 2019)

OK, I'm lost.  Which ICs are we talking about?


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## chongmagic (Nov 15, 2019)

Ok sorry, I was on mobile so it was a little harder, let me start again. 

So I am only getting output on the B side even though the LED is not blinking in sweep B mode. I ran an audio probe on the A side and found that I get a signal from IC5A pin 5. I followed that until R29A and get a faint signal there.


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## Chuck D. Bones (Nov 15, 2019)

So there are at least 2 problems that may or may not be related:
1) No output on A
2) B LED not blinking when in B sweep mode
Do you get signal at IC5A-7?  If you get signal on one side of C14A, but not the other, then C14A is bad or has a bad connection.  Same goes for R29A.  Or OUT A is shorted to gnd.


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## chongmagic (Nov 15, 2019)

Now if I put my audio probe on ICA1 pin 5 I get a wet signal as it should be.


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## Chuck D. Bones (Nov 15, 2019)

Pin 8 is power.  Time to lose the Mobile.


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## chongmagic (Nov 15, 2019)

I meant 5 geez this is irritating lol


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## Chuck D. Bones (Nov 15, 2019)

IC1A pin 5 is the input.  Should only be dry signal there. This is the Duo-Phase, right?


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## chongmagic (Nov 14, 2019)

I am putting together my second Duo Phase, first one worked great, sold it and wanted another. 

LFO A works fine and if I toggle to sweep switch both will work fine. I did sub the B25Ks for A25Ks, but I doubt that is the issue. Looking at the schematic it might be one of my TL072s is bad. I did replace the 4401 transistor just out of curiosity and it still stays constant with the LED if I toggle the sweep switch, the sync switch seems to just make the LED brighter on side B. 

I am still not the greatest with reading schematics, but it looks like if one of the TL072s is bad it would be, IC6B or IC5B.


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## chongmagic (Nov 15, 2019)

Yeah I know and this is the place where the copper was showing a slight trace before I populated the board. I didn't think much of it at the time, but it could be the cause.


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## chongmagic (Nov 15, 2019)

New video by Jonathan Freeman
					






					photos.app.goo.gl


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## Chuck D. Bones (Nov 15, 2019)

The sound in the video is coming from where?  The ch A output or the probe?  Are the two channels separate or wired in series?


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## chongmagic (Nov 15, 2019)

The sound is coming from a Boss looper that I have connected into the audio probe. The other end is a Boss Katana battery powered amp. Two channels are set that they can each be independently connected. Like the four plug wiring diagram in the build docs.


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## Chuck D. Bones (Nov 15, 2019)

So you're using the probe to inject sound from the looper and listening to the output of the Duo-Phase with the Katana?


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## chongmagic (Nov 15, 2019)

Correct

Substituting the looper for a guitar basically


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## Chuck D. Bones (Nov 15, 2019)

I'm used to the idea of connecting the probe to an amp and using it to listen to points in the circuit.  What you're doing is perfectly valid, as long as you inject into parts of the circuit that are relatively high impedance.
What happens if you connect the looper to the Duo-Phase input with a regular 1/4" cable?  Does it work then?


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## chongmagic (Nov 15, 2019)

It only works on the B signal path, no output passes through A.


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## Chuck D. Bones (Nov 15, 2019)

In the video it looks like you installed a 3.9K for both R1A & R2A.


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## Chuck D. Bones (Nov 15, 2019)

If that's not it, then check the wiring of the channel A input connector.  With the stomp switch in the Engaged position, you should have continuity from the input connector to the left side (viewed from the top) of C1A and 3.9K from the right side of C1A to IC1A-5.


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## chongmagic (Nov 15, 2019)

I will double check those and check continuity. I may take a break from this one for a day then come back.


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## Chuck D. Bones (Nov 15, 2019)

I'm going out of town for a few days.  I won't be checking in here much during that time.


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## chongmagic (Nov 16, 2019)

The resistor values are correct and I am getting continuity from C1A to input. Will check the resistance to IC5a pin 5.


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