Hi there... I've got a serious cupcake problem. Short intro, I'm pretty much an intermediate builder at this point, I've built a some madbean, guitarpcb, byoc, and ggg projects, but most of what I do is veroboard. As such, I've done a lot of troubleshooting and I have a pretty good idea of what I am doing. So this problem's got me stumped.
I decided I was going to build an effect in an Altoids box, since I have about a million of them. I dug through my drawer and found the cupcake... populated it, wired it up, and then went to test the voltages before sticking in the opamp and resistor. I get no voltage anywhere on the board. I tested my DC jack when i installed it, and was getting about 9.5v between ground and positive. Now, with the circuit wired to the DC jack, I get no voltage between the lugs on the DC jack, and, like I said, no voltage anywhere on the board. This tells me there's a short somewhere that's pulling 9v to ground. Following the circuit, I started pulling parts, first the filter cap C8, then the rectifier diode D2. Probed pin 8 of the opamp socket which should be +9v, and got 0. Probed R7 which should have +9v at one side and got nothing. Lifted R7, nothing.
I visually inspected the entire thing, but as it's a through-hole, double-sided board, it's cake to solder and wire compared to most of what I do. I reflowed every solder joint, checked for solder bridges (and had another much more experienced EE check for the same) and I still have a short somewhere. At this point I'm fairly convinced there's a short between supply and ground somewhere on the PCB, possibly a manufacturing error. I could remove every component but I'm fairly sure that won't change anything. I've purchased many PCBs through madbean and this is the first one I've found bad. Is there a remedy for such a situation? Is there a troubleshooting step I'm missing?
Thanks.
Do you actually get continuity to ground from the 9v pad on the PCB?
You'd still get voltage at the +9v in pad even if voltage was getting sucked to ground. You'd just ALSO have a component heating up somewhere on the PCB ... so this says to me that there's something wrong with the jack or wire that's carrying DC to the PCB.
Good question, and one I tried a bunch of ways to answer, and the answer is, sort of. I tested this a bunch of times because I was expecting continuity with what I was seeing, but I don't get perfect continuity between ground and the +9v pad with my continuity test on my DMM. It's pretty close, so it doesn't "beep," but it does show some sort of small voltage differential, as it would if I was testing a diode or something with some continuity.
If I remove the wire from the power jack, I get ~+9.5 between ground and the lug. The instant I connect the wire from the board to the lug, I get 0. I do get continuity between the power jack lug and the +9v solder joint on the board, and between the wire end and the solder joint on the board, and ground is working throughout the board. Nothing is heating up that I noticed... I didn't rest my hand on anything specific to check this, but nothing smoked, and I touched or probed everything on the board and don't remember any particular hot spots.