On April 7, 1993, at approximately 1255 central daylight time, a Boeing 757 200, Canadian registration CF00A, declared an emergency following a loss of control after encountering extreme turbulence while in cruise flight at FL 420, approximately 30 miles south of the Houston Intercontinental Airport (IAH), near Houston, Texas. The airplane, operating as Elite Flight 833, was owned and operated by Canada 3000 Airline Limited, as a charter flight from Vancouver, Canada, to San Jose, Costa Rica. There were no injuries to the 31 passengers or 9 crewmembers aboard the airplane. Instrument meteorological conditions prevailed throughout the area at the time of the incident. The captain had turned the fasten seat belt light on and ordered the cabin crew to secure the cabin as the airplane approached an area of forecasted convective activity. Radar vectors were provided around weather and traffic. The captain stated that their airborne weather radar was not displaying severe weather along their route of flight as the airplane encountered light to occasionally moderate turbulence. The airplane was configured for turbulence penetration with engine igniters on "continuous", and manual control of the throttles. A cell appeared ahead of their route of flight, and a 10 degree deviation was requested from ATC and granted. According to the captain, as the turn was initiated to comply with the requested deviation, severe turbulence was encountered, as the airspeed was observed decreasing below .68 MACH. The first officer, who was flying the airplane, "disconnected the auto pilot as both pilots pushed the nose down to prevent the airplane from stalling." The captain estimated a negative 2G force resulted as the attitude of the airplane was changed to an estimated 7 degree below the horizon. As the airplane continued in "moderate heavy" turbulence, both generators came off line and power was lost to all the flight, navigation, and engine instruments. The captain took over the controls and continued to fly the airplane by means of the emergency standby instruments, as he declared an emergency. The first officer started the APU and completed the emergency procedures to attempt to regain electrical power. The flight crew reported a strong electrical fire odor, and an "equipment overheat" message appeared on the ECAS. Approximately 5 minutes after losing the generators, they both came back on line. The airplane was vectored for an ILS approach to runway 14 at the Houston Intercontinental Airport. (breaking out of the weather at 600 feet AGL.) A post incident inspection of the airframe and engines failed to find any anomalies or damage.