What to do when your pots are burning?

cab42 · February 17, 2005, 07:07:19 PM

Hi,

I just had the strangest experience. I was debugging my Tube Reamer, that didn't work, no sound at all, except for some scratching when I touched the strings.

I was working my way through the "what do you do.." sticky when I suddenly smelled smoke. I turned to my soldering iron to see if it touched something, when I turned back I saw smoke coming from the volume pot, and then it started burning and burned for a few seconds.

Well, I guess I found the error in the circuit :roll:

Is it just a bad pot or can something else have caused it? Nothing else on the circuit board was hot or otherwise "strange".

Regards

Carsten

RjM · February 17, 2005, 07:16:50 PM

Check all of your wiring, including the wired that go from and to your battery or DC jack.

Peter Snowberg · February 17, 2005, 09:35:16 PM

Another smoking pot thread.

My guess is that there was a cap missing or a bad cap that was shorted in the circuit.

The scratching you heard from the pot was the same DC flow that caused the burning. This DC is usually blocked by a cap somewhere.

Paul Perry (Frostwave) · February 18, 2005, 01:58:29 AM

The only way a pot can burn (I have done it!) is if you have the centre connected to earth or a power rail, and one end of the pot to the power rail or earth (if you see what I mean..) Everything is OK until the wiper gets close to one end & the resistance across the poer rail to earth gets so low that an enormous current flows & that's it folks!

bwanasonic · February 18, 2005, 03:40:47 AM

Oh, I thought this was a post about that Midnight Oil song, nevermind...

How do I RAWK when my pots are burning?

Kerry M

cab42 · February 18, 2005, 08:29:52 AM

Thanks for the info. Now I know what to look for.

I am building from Torchy's veroboard layout, but with parts taken from a perfboard tune reamer which I ruined when i tried to socket the diodes.

Is there a candidate to which cap i most likely to have been destroyed? I am quite sure that i don't have ant shorts between the traces. Maybe I just should by new caps?

I think the lesson learned from this is: If it ain't broke don't fix it.

Thanks again

Carsten

cab42 · February 18, 2005, 08:32:49 AM

Quote from: bwanasonicOh, I thought this was a post about that Midnight Oil song, nevermind...

How do I RAWK when my pots are burning?

Kerry M

Well, I actually considered give this as a title to the topic, as I also came think of that song.

Great song by the way.

Carsten

Mike Burgundy · February 18, 2005, 09:09:33 AM

suspect *any* cap directly connected to the pot. The trick is to never have DC on pots - they will scratch when manipulated and burn if the current is large enough
Caps should completely isolate the pot from any power supply voltage - usually Vref from IC outputs. A Volume pot is usually hooked up between signal and mass, taking the output from the wiper.
Make sure there is a cap before the pot, in series with the signal. If it is replace it, if there is not, put it there *now*

mojotron · February 18, 2005, 12:57:39 PM

As long as you don't inhale, you'll be fine - it didn't hurt that Clinton dude! :wink:

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What to do when your pots are burning?