Sea Urchin: No Input Signal, Weird Voltage Readings

[whitebread47]

I went to to test my Sea Urchin board this morning.  I get bypass, but no sound whatsoever when engaged.  The first thing I did was check the voltage to the +9v on the board, which read 8.81v; same as DC jack.  I then took readings from both ICs and the Voltage Regulator (I used a 78L05, which as per schematic and data sheet sends the cathode end of D1 to the input of the REG). 

After the readings, I used an audio probe to figure out where I was losing and getting signal at.  There is nowhere on the circuit that I am getting any sound while probed, not even at the input, so I desoldered and wired up the input again for good measure but got the same thing.  I've checked the orientation of all the components, all good.  I also triple-checked my footswitch and in/out and DC jack wiring as well.

I'm not sure why, but the IC readings seem a little funny to me.

Here are my readings:

TL072
1= 6.05  8= 6.64
2= 4.44  7= 6.04
3= 0      6= 6.01
4= 0      5= 0

PT2399
1= 4.95  16= 2.49
2= 2.48  15= 2.49
3= 0      14= 2.49
4= 1.55  13= 2.49
5= 4.94  12= 2.49
6= 2.49  11= 2.49
7= .02    10= .71
8= 4.57   9= 0

78L05
IN = 6.64
Common = 0
OUT = 4.96

Here are some pics:



Sorry, my camera is awful at closeups, making good solder side pics virtually impossible.






Thanks in advance.

[madbean]

Are you sure you have the correct value for R7? It's hard to read the resistor code because the light is bouncing off it.

How about if you remove IC1...do you get 9v on pin8 without the IC in?

[mgwhit]

If you're not getting signal anywhere on your board when the effect is engaged, you probably have a wiring error you just haven't found yet.  One possibility is that you're accidentally plugging into the output jack -- I've done that when debugging an open, upside-down pedal before.

You're also getting 0V on pins 3 and 5 of the TL072, where you should be getting the VB voltage (approximately half of your input voltage), so check for shorts or bad joints near R20, R21 and C21.  Your voltage on pin 8 looks pretty low, too.  I'd definitely test with a fresh battery.  Good luck!

[mgwhit]

I can barely tell, because of the glare, focus and angle, but there looks like there may be a bridge between the positive and negative pads for C21.  If that's not it, can you post a backlit shot of the board.  Might give us a better view.

[gtr2]

Check your components and joints around the powering section of the schematic/board.  You should have close to your 8.8 at the input of the regulator.  (I'm to lazy to calculate the voltage drop from R7)
The TL072 should be close to:

1) 4.5
2) 4.5
3)4.5
4) 0
5)4.5
6)4.5
7)4.5
8)8.8

[whitebread47]

Sorry it took so long to get back to this, had some pressing matters come up after I started this thread.

I read through the responses and finally got the circuit working.  There was a monster of a solder bridge between the +/- pads of C21, as Mgwhit suspected.  After fixing that, I plugged it back in and began smelling a burning plastic smell.  I think I fried the PT2399, because it put out no delay but a clean signal when engaged.  So I replaced it with another and it fired right up.

I'm not sure how I missed that solder bridge and feel bad for mucking up the forum with another thread when the problem was so simple, but thanks a ton for the help.  I learn something new with every build and am slowly working my way through all the Madbean boards (got a Cave Dweller, Mudbunny (GRN Russian spec), and Slow Loris coming up as well.

I'll post a build report once I get the enclosure finished.  This pedal is a gift for a friend of mine who has offered to hand paint a lot of enclosures for me in exchange for a Sea Urchin, and she is really talented, so I can't wait to see and post her work!

[mgwhit]

Glad you got it working!

I've seen a lot of recommendations lately to do an initial power-up without the IC's and check some key voltage test points before proceeding.  I think I'm going to start doing that -- especially on etched boards.  They're just too easy to get solder bridges on.

Have fun -- can't wait to see the enclosures!

[whitebread47]

Thanks!

Hmm, that pre-IC voltage check sounds like a good idea.  I think I'll go that route from now on. 

This delay circuit sounds really cool.  I sent my friend a sound clip I recorded with my phone, and she said, "That sounds AWESOME!!! Omg!!! bring me as many of your pedals to paint as you want."  I can't wait to bring my builds over there to show 'em off, especially since she just bought a Vox Night Train today! 

[micromegas]

something similar happened to me and I decided to go for a Cave Dweller build (it sounds amazing, by the way)
but all the  comments in the forum about how cool it sounds are encouraging me to give it another try

[whitebread47]

something similar happened to me and I decided to go for a Cave Dweller build (it sounds amazing, by the way)
but all the  comments in the forum about how cool it sounds are encouraging me to give it another try

I've built a few delays at this point, and this is by far my favorite circuit FWIW.  I strongly encourage building one.