Greg, allow me to let me enlighten.
FIrstly, AM demodulation is incredibly EASY. That's why those classic
crystal radio sets
from my childhood were so popular. As you've discovered, a poor solder
"cold" joint
can inadvertently create a semiconducting junction, aka a diode - the
simplest way
to detect an AM signal.

Also, the better soldering irons will have their tips tied electrically
to ground/earth.
Since the Casio, whether running off batteries or an
ungrounded/floating ac
adapter, was on, you could have effectively increased the "receiving
antenna"
by connecting the joint in question to you household.

c²

On Jun 12, 2007, at 7:49 PM, afireinthegarden wrote:

> I have encountered a strange anomaly in a casio sk-5 i just
> finished.When i was working on it, i put a soldering iron to a pin
> while it was turned on and it started playing an am talk radio
> station. I took itoff before the solder melted, let it cool and tried
> again and it did it again! The point i was soldering was one of the
> body contact points i had planned and i decided to just go ahead with
> that. One of the wires didnt stick well, and when tinkering it came
> off. I decided to replace it, and when re-soldering it, i broke a
> copper trace and had to replace it with hookup wire wire. However,it
> wouldnt solder to the resistor at the next point on the trace(R20). I
> took it off to solder to it but the legs were just too short and it
> wouldnt work.
> I couldnt find a schematic on the internet (they all linked to
> JMEzine, which wasnt working), so I decided to just replace it with
> wire as, connected to the pin, well and test the effct. The circuit
> turned on and played, and the contact worked fine, so I finished the
> project with the intention of fixing it later. Then, upon completion,
> I was fiddling and trying the contact points and the radio station
> came back in again, just as clear as before!
> I will try to get the frequency next time. For now though, i've
> posted pictures of the points in the body / alligator clip contact
> group i built. The 8 pins in the box to the left attached to small
> bolts which can be connected to each other with alligator clips. The
> three bolts in the box on the right are attached to larger bolts used
> to body contact tothe smaller bolts. The radio station can come from
> all three. The pink wire is the resistor that has been replaced and
> the wire jumper goes from the top point on that to the pin just to the
> left of it.
> I guess my question is: how in the hell might this happen?!
> -Greg
>
>
>