234 Power Management Unit Fault Finding TB8100 Service Manual© Tait Electronics Limited September 200613.8.2 DC Converter with Microprocessor ControlThese checks will verify the correct operation of the:■ DC converter with microprocessor control■ HVDC control and microprocessor card■ standby power supply card.These procedures check the operation of the DC converter when it is undercontrol of the microprocessor on the HVDC control and microprocessorcard which is plugged into the AC converter board. It is assumed that thetests described in Section 13.8.1 have been carried out successfully.Note The AC converter board fitted to a DC PMU is a sub-populatedversion of the complete board which is fitted to the AC PMU andAC and DC PMU. Both types of board work in exactly the sameway for the purpose of testing the DC converter.Note Do not connect the standby power supply card at this stage.In this section voltages are given first for a 12V PMU, followed by voltagesin brackets for a 24V PMU ( ) and a 48V PMU [ ].Task 1 —Check DC ConverterBoard, and HVDCControl andMicroprocessorCard1. Connect the DC module to the AC module as shown in Figure 13.8.2. Ensure that the DC control card and battery control card are pluggedinto the DC converter board, and the PFC control card and HVDCcontrol and microprocessor card are plugged into the AC converterboard, as shown in Figure 13.8.3. Connect the correct DC supply to the input of the DC converter andmeasure the voltage at either PA output connector. The outputvoltage should be 28VDC. If it is, go to Task 2. If it is approximately26.5VDC, go to Step 4. If it is higher than 28VDC, go to Step 5.4. The HVDC control and microprocessor card is probably faulty(because the microprocessor adjusts the output voltage to 28VDC).Replace the card and recheck the voltage. If it is correct, go toTask 2. If it is not, go to Step 5.5. Check that the ribbon cable is undamaged, and is connected securelywith the correct orientation. There is a hole in the PCB beside pin1 of the connector. If the ribbon cable is not faulty, go to Task 3.
