Troubleshooting a dead pedal

[DrKoester]

I have a Pigtronix EP-1 that I am struggling with. I've been back and forth with Dave Koltai who makes it but no luck yet and he wants me to wait til after April 20 to send it to him but I'm too impatient! So here is the problem:

Like a fool I plugged in DC power from my daisy chain because I realized I had an unused plug, it takes 12VAC -- DUH! I have no idea why I blanked on this but I did, no realizing what may happen. So it blew a fuse, a seemingly simple fix. Replaced it, plugged only the power in and all seemed well. Put the cover on and put it back on the board. Once everything was in place, I powered it up again and the lights came on for 1-2sec before dying out. I have since replaced the fuse two or three more times and it blows as soon as it receives power. I also checked the power supply with a multi and it checks out fine. Any thoughts on this?

[Structo]

Is the pedal a negative or positive ground?

Sometimes when pedals are built using PNP transistors they have a positive ground.
There are ways around that to make them work with conventional power supplies but sometimes the makers don't do this

The only clue many times is the little diagram of the adapter plug on the pedal showing the polarity of the plug that needs to be used.

So if you plug in a supply with the wrong polarity you can fry a diode or transistor.
It doesn't matter if it was 12v or 9v, if the polarity was reversed it still did the damage.

[StompBoxBlues]

I think it is a different issue here at play. Very true about dc pedals, but when a pedal is designed to take AC, and gets fed DC, a lot more comes into play. Some component (cap, diode, resistor) got a lot more current than it was designed for and only in one direction.

There is a component probably shorted out, the fuse hangs in there for a few seconds, then blows. it is further on down the line, after the fuse.

The thing is, I have no idea what experience and equipment the OP has. If experienced, and volt-ohm-ammeter one could have a chance, even just ohming out (you don't want to keep replacing the fuse, it is an overcurrent situation and you may be damaging more each time).

if you had a schematic and traced the power (which is the first place I'd look) and see what is what, look for shorts to ground or unusually low resistance to ground at points that seem likely...etc.

It totally depends on what information and experience though.
Likely if someone is asking at this point, it would be very difficult to teach from here how to troubleshoot it.

[DrKoester]

Thanks for the rapid response. I'm definitely still just getting acquainted with circuits. I've built three BYOC pedals but unfortunately a lot of the fundamentals are lost on me and quite frankly soldering-by-number is easy! So while I have the capacity to solder and de-solder and re-solder and diagnose a bad solder joint, I'm only vaguely familiar with schematics. Any good lessons/tutorials out there that you know of? I really oughtta learn this...;) thanks

[Structo]

Sorry I totally missed the ac part.....