Getting shocked at the mic while playing guitar

I'm getting shocked touching the mic while holding the strings. Read all the advise I can find about why and I have tracked it to something in the pedal board. (That is, I get it from different PAs, in different buildings with different guitars and main cables, etc. Proved that if I plug directly into the amp and skip the board altogether then the shock goes away.)
Problem is that I can't break the pedal board down at a gig and then go through all the pieces until I find it, so I'm trying to do it at home with volt meter since I don't have a PA at home.
I'm expecting to see a current between the strings and the wall ground outlet - but I'm not!
Can anyone please tell me how I should use the voltmeter to see the problem so I can then go through the rig until I eliminate it?
Thanks!

I used toget them alot on different gigs. it is either the amp or the pa head NOT grounded or heaven forbid the place we were playing at didnt have grouded outlets. I usually tested the outlet before i plug in any gear to it with a standard outlet tester.
Sounds lke your getting the problem from your Effects board is stilla ground problem. OF course you dont see them with a three way plug cord! My GT 10 nor my GR55 have three way plug and i wa salso getting this tiny zap from it when my elbow was touching something else..and i was adjusting knobs!
BUT...they have a screw on the back fro grounding. Check the back panel of your FX board.. and look for a screw that has a little icon by it that looks like a RAKE heheh i cant describe it anymore then that.
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Something to that effect :O) if you see that ground a wire from that to the power strip if you have one or to anythign around you thats is grounded.. it helped me... IF you DONT have the screw try just using an aligator clip to the Chassis of the FX board and ground it that way :O)

I'm getting shocked touching the mic while holding the strings. Read all the advise I can find about why and I have tracked it to something in the pedal board. (That is, I get it from different PAs, in different buildings with different guitars and main cables, etc. Proved that if I plug directly into the amp and skip the board altogether then the shock goes away.)
Problem is that I can't break the pedal board down at a gig and then go through all the pieces until I find it, so I'm trying to do it at home with volt meter since I don't have a PA at home.
I'm expecting to see a current between the strings and the wall ground outlet - but I'm not!
Can anyone please tell me how I should use the voltmeter to see the problem so I can then go through the rig until I eliminate it?
Thanks!

The mic and guitar are plugged directly into the mixer, I gather by what you're saying, when you receive the shock. This is very common by picking up the 'eddy currents' (if you will) as your body serves as the conductive ground, completing the shared load from the same power supply (board).
Use carpet, plywood or rubber mats to run the ground from your mic stand as well as your feet. The mixer and any electrical equipment should not be in contact with earth ground or cement at all as it only serves as an extension to the ground circuitry to where current is drawn. Also, balanced and well shielded instrument and mic cables will help. Hang speaker wires off the floor.
Even for sound preservation (to omit the ground 'buzz') you should use a separate breaker outlet for the power amp, whenever possible.
Oh, your voltmeter leads may not be long enough to check for the 'zaps'.