Help me troubleshoot

[soggybag]

I built an Ugly Face. I tested it for about 15 minutes. Everything worked fine no problems, sounded good. I gave it to someone else. They played with it for an hour, and it stops working?

I test the thing and there is continuity across the battery snap!

I take the 7555 out and test it in an Uglyface I has been playing with on a bread board. The chip seemed to work, but it make a very strange unsteady oscillation constantly. Very weird.

Nothing looks obviously burnt or fried, and nothing got hot when I connected it to a battery. Though the battery started getting warm which was first clue.

[newfish]

A warm battery would indicate a short somewhere - as indicated by the battery snap giving continuity.

I'd start by checking that the board hasn't moved in transit - allowing a short to develop (through the case, for example...)

[petemoore]

  Had the same deal w/d sumbish.
  Close in Hi-Intensity lamp and a Mag-Glass, and a cup of coffee..
  Take your time and search around first, second...
  Other than luck of the find I didn't have, my searches had me fairly confused for some time, then I resorted to lifting wires connected to the power supply rails, an elimination / verification process...ie if the short continues, keep looking, when the shorting condition ceases...you've narrowed the search and you're nearer the actual fix.

[soggybag]

This is driving me nuts. Everything looks fine. There is no obvious damage.

[Joe Kramer]

A short in the battery connector?

A tantalum capacitor failure?  IIRC, electrolytics fail open, but tantalums fail closed, creating a dead short.

Just throwing a couple things out there. . . .

Regards,
Joe

[fogwolf]

Is this in a metal case? If it's a tight fit is something possibly shorting out against the lid when you seal the box up? If you have a DC jack is that wired correctly? If you have a warm battery there is a short somewhere.

I built an Ugly Face. I tested it for about 15 minutes. Everything worked fine no problems, sounded good. I gave it to someone else. They played with it for an hour, and it stops working?

I test the thing and there is continuity across the battery snap!

I take the 7555 out and test it in an Uglyface I has been playing with on a bread board. The chip seemed to work, but it make a very strange unsteady oscillation constantly. Very weird.

Nothing looks obviously burnt or fried, and nothing got hot when I connected it to a battery. Though the battery started getting warm which was first clue.

[soggybag]

Thanks for the suggestions.

Last night I noticed the short was gone. But if I connected it to a power supply it was shorting, which was very strange. So I took out the two chips and tested again. I figured that this would eliminate them as the problem, if the short was still there without them. The short was still there.

At this point I checked the reverse protection diode, which is something that I had been thinking about checking earlier. I took this out and tested again, no short. Everything seemed to be working again.

So my guess is, someone connected this to a reverse power supply.

That said it is very strange that after being connected to a power supply the diode would show a short with the multimeter. But after sitting over night this effect would go away? I distinctly remember testing the two connectors on the battery snap and getting continuity the day before. I tested it a few times. The next day no continuity. Just before testing I had the thing connected to a battery for 30 seconds or more before I realized the battery was getting warm. Which was what tipped me off to the short.

I was using the typical diode off the + on the power supply to ground, that you see everywhere. I remember reading a post by Zvex sayng that they took out this type of protection diode from the Box of Rock because it was causing more damage than without it. Maybe the inline diode os a better choice?

[Joe Kramer]

On the subject of diodes, I once had a 1N914 that was marked backwards, with the black band on the anode!   Nearly broke my mind trying to figure out what was wrong with the circuit until I discovered it.  Even then, after I traced it down and fixed the problem, I still couldn't help sulking over the idea that, out of the milions, possibly billions of those that have been made, I had to grab the bad one!  What a nightmare that was.  Anyway, needless to say, now I test each and every diode before use.

Probably not relevant to your immediate problem, but good to know anyway! . . .

Regards,
Joe