Bacon Bits Returned Roasted Resistor

[claytushaywood]

I built a bacon bits about 2 months ago.  The most magical sounding boost pedal I've ever used.  I didnt understand why people thought boosts were so magical until I built this pedal actually.

I wanted to share that joy with a friend, I let a buddy borrow it.  He returned it to me saying I dont know what happened it just stopped working. 

I opened it up and sure enough R10 is fried to a crisp.   

My first question is what causes this?  Plugging in a higher voltage power supply?  Or one putting out too much current?  Or is that from daisy chaining with the wrong polarity?  I'm asking this because he always seems to have trouble with power supplies, and ive seen him using a lot of those 1 spot "reverse polarity converter"

And what all do I need to replace to get it working now?  Are my opamps likely fried?  diodes?  Any idea where to start besides the burnt up 47ohm resistor?

Thanks a bunch!

[claytushaywood]

also wondering if anyone can point me in the direction on how to test power supplies.  I know how to measure voltage of course, but how do you measure the current a supply is giving off?

[Luke51411]

I would guess probably reverse polarity, possibly overvoltage, or AC instead of DC. The adapter will only put out as much current as is being demanded, if too much is being demanded, I think the adapter would fry. I don't really know what I'm talking about though but I'm sure someone who knows more will chime in soon.

[mgwhit]

Luke's right about current.  You can provide too little current, but not too much.

Where did you get your 12V Zener diode (D2)?  If it failed and shorted to ground, it would pull enough current through R10 to fry it.  If that's what happened, you can just clip out D2 and replace (or even jumper) R10.  D2 is unnecessary as long as you don't provide more than 12V from your power supply.  The good news is that nothing else should be harmed if that's what happened.

This kind of failure has happened a lot with boards that are using Zener diodes for overvoltage protection, primarily because there seem to be a lot of crap Zener diodes on the market.

Reverse polarity should not have killed it thanks to the inline 1N5817 diode (D1).