Tait TP9100 Service Manual

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180 Frequency Synthesizer Fault Finding TP9100 Service Manual© Tait Electronics Limited May 2005Task 14 óCheck FeedbackVoltageIf the loop filter is suspect but the reference voltage is correct, check thefeedback voltage.1. Measure the feedback voltage at pin 6 of IC505 (see Figure 9.9).The result should be:2. If the voltage is not correct, the loop filter is faulty; go to Step 3.If the voltage is correct, resolder R542 in position (see Figure 9.8)and go to Task 15.3. Check IC504, IC505, Q511 (see Figure 9.9), C548(see Figure 9.8), and associated components.4. If a fault is found, repair the circuit, repeat the measurement of thefeedback voltage in Step 1, and resolder R542 in position(see Figure 9.8).5. If the feedback voltage is now correct, go to “Final Tasks” onpage 134. If it is not, or if no fault could be found, replace the mainboard, and go to “Final Tasks” on page 134.IC505 pin 6: 2.5 ± 0.1V DC