Duo Phase LFO B Constant LED

[chongmagic]

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.

 

[chongmagic]

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

 

[JetFixxxer]

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.

 

[chongmagic]

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.

 

[Chuck D. Bones]

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

Yes.
Visual inspection.

 

[chongmagic]

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

New item by Jonathan Freeman (Chongmagic)

photos.app.goo.gl

 

[chongmagic]

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

 

[Chuck D. Bones]

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

 

[chongmagic]

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.

 

[Chuck D. Bones]

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.

 

[chongmagic]

The resistance is correct

 

[chongmagic]

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

 

[chongmagic]

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.

 

[Chuck D. Bones]

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

 

[chongmagic]

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.

 

[Chuck D. Bones]

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.

 

[chongmagic]

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

 

[Chuck D. Bones]

Pin 8 is power. Time to lose the Mobile.

 

[chongmagic]

I meant 5 geez this is irritating lol

 

[Chuck D. Bones]

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