Flapjack DOA: No LED, no effect

[lincolnic]

I was hoping I'd never have to make a thread like this, but my time has come. I built up my Flapjack today (no parts substitutions), super excited, and...it just doesn't work. I get signal in bypass, but with the switch engaged, I get no sound and the LED doesn't light up.

I've never had a build not fire up immediately, so I was cocky and boxed it up first (I know, I know). I've double-checked my wiring, parts orientation, and component values. I don't quite understand how to take DC readings with my meter, but I checked continuity between all my wiring points and that's all fine. I also checked continuity between the lugs on my 3PDT, that's fine too. The fact that the LED doesn't light up makes me think that maybe the board isn't getting 9V, but I've got continuity between my jack and the board.

I tried probing around with my signal tester, but my skills were only meager enough to take it through the first two resistors...then I got overwhelmed.

Any help would be much appreciated. Sorry in advance for the picture quality:

[greyscales]

I've had a lot of problems with DC jacks having a bad lug. Make sure you connect them with a resistor leg or something like that.
If it isn't that though, someone else will have to help you.

[mgwhit]

If the effect works in bypass, but not in effect mode and the LED doesn't light up, you've at least got a power problem, and you should debug that before every thing else.  The good news: this is easy.  Put away your signal tester -- it's time to learn how to take DC voltage readings.

Set your DMM to the most appropriate DC voltage test setting -- greater than the voltage you're testing for, but not ridiculously higher.  On my DMM it's 20VDC.

Connect the black lead to a ground point.  If you've got alligator clip leads, this is very simple -- just clip it to the ground point on your power jack.  Otherwise, you just need to hold it against the ground point, but that's harder than it sounds.  You'll inevitably lift it while you're taking a reading.  So if you do it that way and you get a strange reading, go back and make sure you still have ground contact.

Now touch the red lead to any point you want you want to read the voltage at.  Test the voltage right at the jack, where your power wire connects.  Now test it at the board 9V input point.  Test it at the LED's positive lead (with the effect activated).  I'll have to go dig up thread with the build doc for this board, but other good places to check are the pins of the IC.  The 741 should have 9V on pin 7 and 0v on pin 4.  Good luck!

[lincolnic]

Well, I solved my problem. I had double-checked everything at the time, but I must've been too frustrated to see clearly. Coming back to it a couple of hours later, I immediately saw I'd wired my 9V wire to the wrong lug on my DC jack. Everything works beautifully now. Moral of the story: just because you double-checked it doesn't mean you didn't miss the problem twice in a row!

Thanks for the lesson on measuring DC, Matthew. It makes perfect sense now.

Build report to follow!

[whitebread47]

Well, I solved my problem. I had double-checked everything at the time, but I must've been too frustrated to see clearly. Coming back to it a couple of hours later, I immediately I'd wired my 9V wire to the wrong lug on my DC jack. Everything works beautifully now. Moral of the story: just because you double-checked it doesn't mean you didn't miss the problem twice in a row!

Thanks for the lesson on measuring DC, Matthew. It makes perfect sense now.

Build report to follow!

Glad you got it to work!  I had a similar problem that I had "triple checked" to no avail, so I took a day break from it.  I was just about to start a thread on it when I found yours.  After reading, I gave all the connections one more look and the ground wire wasn't connected to the footswitch lug properly.  I'm glad you started this thread, though, as mgwhit's post is helpful for future reference.

[lincolnic]

Glad you got it to work!  I had a similar problem that I had "triple checked" to no avail, so I took a day break from it.  I was just about to start a thread on it when I found yours.  After reading, I gave all the connections one more look and the ground wire wasn't connected to the footswitch lug properly.  I'm glad you started this thread, though, as mgwhit's post is helpful for future reference.

Glad you got yours working too! I just wish I'd gotten mine up sooner, when there was still time left in the day to properly test it out. It was already late-ish here, so I could only turn it on long enough to verify everything sounded right. I'm busy all day tomorrow, so it'll have to wait until Tuesday before I can play it at a proper volume. I'm really looking forward to it!