Andre's, I'm not sure what Argentina uses for power distribution, but if you can measure 100 volts from EITHER pin to ground, it's possible you have 3-phase power distribution. If the two pins measure DIFFERENTLY to ground, then you have likely an un-balanced load on the power. This can be caused by having too many devices on one phase compared to the other. this condition can only be fixed by either plugging certain things into other outlets, or it may be caused by a bad transformer or motor that's shorting out part of the power.
With 3-phase distribution, each phase is 120 degrees away from each of the other two. If you use two of the 3 phases, since they are not 180 degrees out of phase, each phase, measured to ground, will be MORE than half the nominal voltage - here in the US for example, industrial 3-phase 440 volt power measures 277 volts to ground. This is using Delta type transformers. There is a "Y" method of wiring, where one winding of the transformer is center-tapped to ground, with 208 volts between legs, and 120 volts across each leg. If you get the wrong leg (phase) to ground with this system, you get about 177 volts if I remember correctly. Here, the "Y" system is only used in commercial places, like restaurants, stores, etc - the Delta system is used in industry, since it's easier to wire and implement and stays balanced with less effort.
In your case, having LESS than half the nominal voltage from one phase may indeed signal a grounding problem. I would (carefully, this stuff kills) measure the OTHER leg to ground, and if they are NOT the same, TURN OFF the power at the service entrance so that your whole house is dead and set your meter to read OHMS x 1 - find a metal water pipe that makes contact with the earth, and measure from that to the ground pin on your power outlet. It should measure ZERO ohms, same as if you touched the two leads of the meter together. If not, your main electrical ground is bad.
There should be a metal (copper, usually) rod driven into the ground near where the power comes into your house - there should be a (sometimes bare) copper wire clamped to this rod and connecting to the ground bus inside the power panel in the house. If this looks at all corroded, do NOT dis-connect this wire or touch it - you will probably get a shock. Instead, contact your power company and have them re-attach the wire properly, after cleaning the connections. Make sure your main dis-connect switch (or main breaker) to the house is open (OFF) before doing this.
If you have grounding problems in your wiring, and you ground your synth, you may either get shocked elsewhere or possible start a fire. At the very least, you will most likely damage the synth.
In cases like this, you need to actually FIX the problem, not put a band-aid on it. Remember, electricity KILLS - you don't often get a second chance to do it right the SECOND time... Steve
