400 Fault Finding of Control Head TM9100 Service Manual© Tait Electronics Limited August 200514.2 Power Supply FaultyA 3.3V regulator (U1) converts the switched 13.8V supply from the radiobody to 3.3V. A 1.5V regulator (U203) converts the 3.3V to 1.5V.A power-sense module (U202) verifies the outputs of the voltage regulatorsand—in the case of a fault—creates a power reset signal which is processedby the FPGA. If the start-up of the control head fails, the radio body reducesthe switched 13.8V supply shortly after power is supplied.For all faults, check that the supply voltages are correct:1. Check the 3.3V supply voltage between E202 and C210.If the signal is correct, continue with step 4.If the signal is not correct, visually inspect the components E202,D201, L201, R205, and R206 for open or shorted contacts.Replace if necessary. Continue with step 2.2. Check the 13.8V supply voltage (9.7V to 17.2V) between pin 2 ofthe control-head connector J103 and pin 8 of U1.If the signal is correct, continue with step 3.Note A fault in the control head can cause the radio body to reduce theswitched 13.8V supply shortly after power is supplied. In this case,the control head must be supplied directly through pin 2 of con-nector J103.Figure 14.1 Circuit diagram of the power supply circuitryJ1036213V8 L1C205C207C11 D1R16R17R208Q201C206C12C13R18INHCOMPSYNCVCCGNDU1 VREFFBOUT24381657 GNDL201D201R205R206C14+E202C2103V3IN OUTU203EN RSTGND3 612 453V3PFI U202 PFOMR RSTWDI WDIGND53 16 78 24E203 1V5C204R201S201 D203D203K1K2AAAA3V3FPGAR210C201C202R202R204DNIPWR WDTMRPWR RESET1V53V312R203Control-HeadConnectorE202/C210: 3.3VJ103 pin 2: 13.8V (V s =9.7V…17.2V)U1 pin 8: 13.8V (Vs =9.7V…17.2V)
