My board is SMOKING!!!

[Bucksears]

and not in a good way..... :?
I built Doug Hammond's Vox EXP and was about to try it out.....when I smelled something. .....
I noticed that where the battery was grounded to the board had a fine stream of smoke rising, so I disconnected the battery. The spot where the (neg.)ground wire was soldered was very hot. This was just after a few seconds.
I wasn't sure if it had something to do with the (+) and (-) being so close on the board, so I soldered the negative wire to another grounding spot. This time, the hot spot appeared in another location. I've gone over my layout a number of times and I'm pretty sure I've gotten it correct.
Has anyone else ever had this problem? HELP!!

[aron]

Somewhere you have a direct short to ground.

Without the battery connected, take your meter and put it into continuity mode (so it beeps) and put the black wire on ground and touch the red probe to the major points to that connect to power from input to output on the circuit.

Alternately, set it to ohms and see if you see suspiciously low ohm readings when probing these points.

That's a start.

If you see low ohm readings or continuity from power points to ground, there's your short.

[Paul Perry (Frostwave)]

I got a bad batch of PCBs once (double sided, with one side out by a bit & slewed!) so I have had "too much" experience tracing power shorts
and, the hint is: "divide and conquer". Cut thru the trace somewher in thepower rail & then see which half of the board is shorted. then keep cutting in half.
Don't forget to join the traces back up afterwards (yeah, done that...!)I have tried "low ohms" testers too, but not worth it in my experience.

[Bucksears]

Thanks guys. I've double checked the schematic vs. the layout and I must be missing something; I'll keep looking.

[Zero the hero]

Check the polarity of polarized capacitors. Once I inverted one of them on a power supply unit and the IC got so hot that when I touched it I felt very bad....

[petemoore]

It;s never a bad idea to check for non-continuity [with DMM] between + and - ... takes about two seconds and can make the whole project less...'stinky'.
 I got in the habit of glancing the battery across the clip, checking for sparks...one teeny little spark can tell you alot about wires that are starting to fry, but 'are' still intact...finding the little gremlin can be tricky... but give him power and hell start eating your ckt, often in places other than the actual miswire.

[Peter Snowberg]

I power up most prototypes for the first time with a lightbulb in series with the power. When the lamp is cold the fillament has a very low resistance and it raises quite a bit when heated. If you don't have any shorts, the bulb never comes on and it just acts like a small resistor. If you have a short, the lamps lets you know and it limits the current at the same time. It's somewhat like a circuit breaker, but it limits current instead of cutting it off.

You have to size the lamp for the current you expect your project to use. Start with a lamp that takes a couple or a few times the expected draw.

-Peter

[Bucksears]

Thanks everybody; you know when you've been looking at something for a while that you miss what's STARING YOU IN THE FACE?  :roll:
A small drip of solder made it's way onto the 'ground track' that's going around the layout. I removed that and it's not heating up anymore, but it's still not working. Back to the workdesk.....
Thanks!

[Ansil]

I power up most prototypes for the first time with a lightbulb in series with the power. When the lamp is cold the fillament has a very low resistance and it raises quite a bit when heated. If you don't have any shorts, the bulb never comes on and it just acts like a small resistor. If you have a short, the lamps lets you know and it limits the current at the same time. It's somewhat like a circuit breaker, but it limits current instead of cutting it off.

You have to size the lamp for the current you expect your project to use. Start with a lamp that takes a couple or a few times the expected draw.

-Peter

very good idea..