416 Fault Finding of Control Head TM9100 Service Manual© Tait Electronics Limited August 200514.11 Volume Control FaultyThe voltage level of the volume control potentiometer is converted to adigital signal by an analog/digital converter, processed by the FPGA andtransmitted to the main board.Note This section only describes faults to the volume control caused bythe control head, which has been established during the initialservicing tasks by means of elimination test. For fault finding ofthe amplifier circuitry of the main board, refer to xxx on page yyy.If the volume control works only intermittently, works only at full volume,or does not work at all:1. Check that the voltage between pins CW and WIP of the volume-control potentiometer RV1 varies linearly between about 0V and3.3V.If the voltage is not correct, replace the potentiometer RV12. Send CCTM command 1010 to read the volume potentiometer.If the signal is not correct, remove can E100 and replace theanalog/digital converter U601.If the signal is correct, replace the speaker.Figure 14.15 Circuit diagram of the volume control circuitryRV1: 0 to 3.3VNo volume: reading 0 (1V)Full volume: reading 255 (3.3V)FPGA ADC DO U601CH13VCC8DO 643V33V3VOL WIP DCR105RV101
