Thanks a lot RaSTuS for the advice, the toggle switch has been a common denominator in nearly every site with the same complain. But I just want to verify with the TS on how he fixed his Epi and what progress he has. Also, this way I can fix the EPI in the cheapest way.
As stated by the TS, it would occasionally happen and come back after a few seconds (which I also experienced) and by the time you have opened up the cavity and check for continuity, every thing turns up to be fine. In my experience, there were times that even if I havn't switch the toggle, the sound will be lose for a few seconds.
Not to brag about, but I feel really ashamed if I was to go to a guitar tech and let them fix something electrical that I could have already done. I was thinking of changing every electric parts in the unit to hit all the birds with a single stone. Plus avoid soldering and unsoldering if the problem would arise again. But then again, it would take a lot of time and cash to complete and lessen my practice time for our coming gig.
Thanks again for the reply,
P.S. how about the crimp connection for the pot cavity and the upper toggle switch cavity? I'm kinda suspecting that also to be the culprit :-)