hot battery?

CoolJohnny · June 01, 2007, 06:59:43 PM

putting together an tim escobedo boostrapped gain. bypass works fine. effect in gives no sound and battery gets really friggin' hot. have never encountered this before. solder joints seem okay, ditto parts orientation and switch leads. any ideas? anyone come across this? pulling my hair out because i've built three of these before with no problems....oy vey!

Paul Marossy · June 01, 2007, 07:01:04 PM

A hot battery is a dead giveaway of a shorted power supply. Usually, that happens when your +9V is shorted directly to ground. And it is also why your circuit isn't doing anything at all.

jlullo · June 01, 2007, 07:18:15 PM

cool johnny, is your switch oriented correctly? my first pedal i had it rotated 90 degrees and this happened...

the lugs should have the holes going up and down... not left and right.. does that make sense?

foxfire · June 01, 2007, 07:35:27 PM

yup, holes up and down. good luck with it and your newest addiction.

Paul Marossy · June 01, 2007, 08:19:58 PM

Wiring your switch wrong shouldn't make your battery hot...

darron · June 01, 2007, 08:41:08 PM

are you using a DC jack also? if so, is the outer (positive) casing of it touching the enclosure (which should be grouneded with negative)? that would do it...

Barcode80 · June 01, 2007, 10:18:02 PM

Quote from: Paul Marossy on June 01, 2007, 08:19:58 PM
Wiring your switch wrong shouldn't make your battery hot...

it does when you switch pos side of LED instead of ground but you are using the grounded input wiring technique

Paul Marossy · June 01, 2007, 10:45:46 PM

Quote from: Barcode80 on June 01, 2007, 10:18:02 PM
Quote from: Paul Marossy on June 01, 2007, 08:19:58 PM
Wiring your switch wrong shouldn't make your battery hot...
it does when you switch pos side of LED instead of ground but you are using the grounded input wiring technique

Oh yeah, I know that. What was I thinking?!

jlullo · June 01, 2007, 10:49:05 PM

that happened with the first pedal i built... it fried the LED, trannys, diodes and opamp

not a fun situation for a beginner!

vortex · June 02, 2007, 12:15:33 AM

First thing I like to do when I "fire up" a new build is to plug it in and just hold the battery to see if it is warming up. If it does, I unplug it immediately to avoid frying other components. You can save an IC or weakening other components when there is a + battery to ground issue.

petemoore · June 02, 2007, 08:28:15 AM

DMM Test for shorting across the power rails, then power up if none are found.
If you find a short, finding the cause of it is sometimes a visual spotting of it, otherwise you may have to lift connections and run tests to find the miswire.
Look for anywhere the ground and V+ can go, 'peripherals' like DC jack and LED are not exempt...with their connection assignments being across the supply rails.

R O Tiree · June 02, 2007, 08:30:06 AM

Has this schematic got a diode connected directly from +9V to Ground? If so, it could be that you have wired this in the wrong way round. It is supposed to be reverse-biased, to act as a cheap and cheerful polarity protection. If it's the wrong way round, the battery voltage just gets shunted straight to ground through the diode. If so, I'd replace it anyway, because high current (why your battery got hot) ruins them.

If there is no diode as described, then there a few more options to investigate.

1. You did connect the battery the right way around? Easily done... If this is the problem, you've probably fried the opamps, diodes and electrolytic caps, possibly any transistors in there, as jlullo says.

2. Check you put the opamp(s) the right way round. They get toasty-warm when wired up backwards. Again, if this is so, replace them.

3. As suggested before, check for a solder-blob that would cause a short from one track to another. Use a bright light and a magnifying glass.

4. Finally, check the circuit backwards, forwards, sideways... Work initially from the schem to the board, checking each junction in turn. Then check it backwards, working from board to schem. If there's an error, you'll find it.

oldrocker · June 02, 2007, 02:08:26 PM

Before I plug in the battery on a new build I continuity test across the battery clip and or the positive and negative portion of the circuit for a direct short. I saved myself some problems making a habit of doing that. It's really amazing how fast the battery can heat up. I noticed that after heating up for longer periods that the battery (if it still works) seems to lose some of its voltage power. I once had 8.7 volts and after I realized it was getting hot I retested the voltage and it was giving out only 7.9 volts.

Paul Marossy · June 02, 2007, 05:23:49 PM

QuoteIt's really amazing how fast the battery can heat up. I noticed that after heating up for longer periods that the battery (if it still works) seems to lose some of its voltage power. I once had 8.7 volts and after I realized it was getting hot I retested the voltage and it was giving out only 7.9 volts.

I found the same thing to be true in my experience.

CoolJohnny · June 02, 2007, 09:27:34 PM

thanks for all the input folks. after a frustrating hour or so with it yesterday i decided to put the thing down for a day or two. this always seems to help.

the most obvious culprit in my estimation would be a solder blob (my tip probably needs to be reitred i admit) or some kind of short in the circuit pathway itself.

neither of the two succesful previous builds of this circuit are in my posession right now (lent to friends who live far away) but i may have to get one mailed if i cannot solve the issue soon...its a sweet-sounding box.

will report back if further help needed. thanks again...

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hot battery?