256 Receiver Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 2005
Task 5 —
Check Biasing
of IF Amplifier
If the lock status is normal, check the biasing of the IF amplifier.
1. Remove the
IF IQ BOT can.
2. Check all components around Q404 of the IF amplifier
(see Figure 11.1).
3. Check the 3V supply voltage at L419; use the measurement point
shown in Figure 11.1.
4. Also check the amplifier bias conditions. First measure V
c
between
the collector of Q404 and ground (see Figure 11.1).
5. Secondly, check I
c
. To do so, unsolder and raise one terminal of L419
(tombstone position) (see Figure 11.1), connect a multimeter
between this terminal and the pad for the terminal, and measure the
current.
6. If the checks in Step 2 to Step 5 reveal no fault, go to Ta s k 6
.
If there is a fault, repair it and go to Step 7.
7. Recalibrate the receiver using the calibration application.
8. Confirm the removal of the fault and go to “Final Tasks” on
page 134. If the repair failed, go to Tas k 7
.
V
c
: 2.0±0.2V
I
c
: 1.8±0.5mA
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