Tait TP9100 - Page 142

142 Interface Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 2005
Task 4 —
Volume Control
Faulty
Use this procedure if the volume control works intermittently, works only
at full volume, or doesn’t work at all. These symptoms can indicate a fault
with the volume pot, or the CODEC and audio circuitry. Before
proceeding, make sure the Minimum Volume Level is not set to 255 in the
programming 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 test
points
TP908 and TP907. See Figure 7.1.
4. Vary the volume control position between extremes, and measure the
resistance. The correct ranges are below:
5. If the control resistances are outside these limits, replace RV1. If the
resistances are within the limits then the volume control is not faulty;
go to “CODEC and Audio ault Finding” on page 269.
Task 5 —
16-Way or 3-Way
Selectors Faulty
Use this procedure if the radio fails to change the channel when the 16-way
selector is turned, or the zone when the 3-way selector is turned.
Before proceeding, make sure there is more than one channel and zone
programmed for the radio, and those channels and zones have been assigned
to 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-way
selector) 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-way
selector is rotated. Depending on the selector position, each pin
should switch between the following logic levels:
5. If the logic levels are not correct then replace RSW1 and retest. If the
logic levels are correct, or replacing RSW1 does not repair the fault,
replace the main board.
resistance at extreme limit (low): < 50Ω
resistance at extreme limit (high): > 9kΩ
16-way selector: pins 1, 2, 4, and 8
3-way selector: pins A and B
logic level low: <0.5V
logic level high: >3.0V