kenwood_ts-930s_control_circuit_tests

TWO SIGNAL BOARD TESTSThere are a couple safety circuits that are designed to protect the PA.The circuits are circled in red belowand on the photo on the next page.The connectors are outlined in yellow.The larger one is the Automaticlevel Control (ALC)from the LPF.ALC TEST:The ALC level is controlled by a feedback circuit from the Power Amplifier and the LPF.Itreduces the drive from the Signal Unit to the PA as the SWR increases,and it will shut the drive downcompletely if it believes that the SWR is too high,there's a short at the antenna terminal or there's a faultsomewhere else in the output circuit.A simple test is to remove the ALC plug from the right side of the LPFwith the power off.The connector is outlined in red,below.The rig is then turned back on.With the carrier control "off'(fully counter-clockwise),the rig is set toSEND,and the carrier SLOWLY increased.If the output power climbs to 100 watts or more as the carriercontrol is advanced,then the problem is in the LPF,or in the ALC circuit in the Signal Unit.Care is neededhere because the power can go over 150 watts with that plug removed,which could damage the finals.CURRENT CONTROL (ICA/ICB)The other power control circuit is the current limiter (ICA and ICB)which comes from the connector on the AVR board.This circuit,which shuts down the drive to the PA inthe event of a current overload,is maintained while rebuilding the AVR board after the Quint conversion.This circuit receives the main voltage and a slightly lower one from the voltage drop across that 0.05 ohmpower resistor in the PA supply line.The gray wire from that resistor goes to the 3-pin connector on theAVR board,through one of the green inductors,and then down to the signal unit via the brown wire.The28.5V B+goes passes through the other green inductor down to the Signal Unit via the white wire.A simpletest to see if this circuit is malfunctioning is to unplug the two-wire ICA/ICB connector (with the power off).The rig is set to SEND and the carrier control slowly eased in.If the power returns to normal,then theproblem is either in the voltage output from the AVR board,or a bad component on the Signal Unit board