Most original EFIS tubes include older tube technology with a high voltage power supply (HVPS) and a CRT (cathode ray tube). Because units with CRTs can operate at high voltages they can be susceptible to significant failure. When failures in the power supply occur, they usually must be replaced. The failure can lead to problems in the CRT assembly itself as well.
In most cases, SEA exchange prices reflect the assumption that the HVPS will need to be replaced in the defective unit. Based on SEA’s historical data, approximately 75% of defective EFIS indicators will need to have the HVPS replaced but not necessarily the CRT. However, in most cases where the CRT must be replaced, then the cost is more than a replacement unit thus rendering the defective unit beyond economical repair (BER).