Tait TP9100 Service Manual

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142 Interface Fault Finding TP9100 Service Manual© Tait Electronics Limited May 2005Task 4 óVolume ControlFaultyUse this procedure if the volume control works intermittently, works onlyat full volume, or doesn’t work at all. These symptoms can indicate a faultwith the volume pot, or the CODEC and audio circuitry. Beforeproceeding, make sure the Minimum Volume Level is not set to 255 in theprogramming application. This will result in a maximum volume level,regardless of the position of the volume control.If the volume control is faulty:1. Remove the front panel and main-shield assembly.2. Remove power from the radio.3. Connect a resistance meter (such as a multimeter) across the testpoints TP 908 and TP 907. See Figure 7.1.4. Vary the volume control position between extremes, and measure theresistance. The correct ranges are below:5. If the control resistances are outside these limits, replace RV1. If theresistances are within the limits then the volume control is not faulty;go to “CODEC and Audio ault Finding” on page 269.Task 5 ó16-Way or 3-WaySelectors FaultyUse this procedure if the radio fails to change the channel when the 16-wayselector is turned, or the zone when the 3-way selector is turned.Before proceeding, make sure there is more than one channel and zoneprogrammed for the radio, and those channels and zones have been assignedto different positions on the 16-way and 3-way selectors.If the 16-way selector or 3-way selector is faulty:1. Remove the front panel and main-shield assembly.2. Power up and turn on the radio.3. Connect a multimeter or oscilloscope to pins 1, 2, 4, and 8 (16-wayselector) or pins A and B (3-way selector) of RSW1. See Figure 7.2.4. Check the voltage on the pins as the 16-way selector or 3-wayselector is rotated. Depending on the selector position, each pinshould switch between the following logic levels:5. If the logic levels are not correct then replace RSW1 and retest. If thelogic levels are correct, or replacing RSW1 does not repair the fault,replace the main board.resistance at extreme limit (low): < 50Ωresistance at extreme limit (high): > 9kΩ16-way selector: pins 1, 2, 4, and 83-way selector: pins A and Blogic level low: <0.5Vlogic level high: >3.0V