||The importance of fracture characterization in geothermal logging has long been recognized. The acoustic borehole televiewer is probably the single most useful tool for determining location, orientation and characterization of fractures. However, since the televiewer was developed for low temperature oil and gas exploration, it has not been capable of reliable operation at geothermal temperatures. This paper reviews the theory of operation of the acoustic televiewer, identifies the problems associated with its operation at both high and low temperatures, and reviews a program to upgrade the tool. Major results of the program have been: 1) a high temperature acoustic transducer, 2) an improved acoustic window, 3) more reliable electronics, and 4) the elimination of troublesome slip rings.