Boeing Co 767-338ER, VH-OGC

The Boeing 767 had just reached cruise altitude at flight level
330 approximately 40 minutes out of Singapore enroute to Perth,
when the flight crew noted smoke and electrical fumes on the flight
deck. The source of the smoke and fumes could not be readily
identified. The pilot in command elected to have the flight crew
don oxygen masks, and diverted to Jakarta.

The operator's engineering personnel examined the aircraft and
found the right DME (Distance Measuring Equipment) circuit breaker
open. Technicians isolated the problem to the right DME
interrogator unit. The malfunctioning DME unit was disabled in
accordance with the MEL (Minimum Equipment List) guidelines to
allow the aircraft to continue to Perth. Following arrival in
Perth, the unit was replaced.

Examination of the unit by the manufacturer revealed that the
DME unit's A5 modulator had overheated. This failure mode was
similar to two other units, which had overheated on a different
aircraft in January 2000 (see Occurrence 200000055). The failure
mode of those units was such that the A5 modulator had overloaded
the positive 86 volt DC power supply and overheated the power
transformer. Compliance with service bulletins recommending product
improvements to this unit were not mandatory, and the recommended
modifications had not been incorporated into this unit, or the
previous two units that had sustained failures.