User Manual

SERVICING

5-4

Part No. 001-3422-003

Figure 5-1 RECEIVER SERVICING

5.3.3 SECOND LO (Q401)

Verify that the Second LO signal is present at U241, pin 4. The Second LO should be at 21.90 MHz and not

less than 500 mV P-P.

5.3.4 AUDIO BUFFER AMP (U241)

The Data output on J201, pin 13 should be 100-200 mV RMS, with the preceding injection signal. If these

levels are not correct, verify proper adjustment of L253 (see Section 6.7). The gain of U241 is 2.8 for 30 kHz

radios and 5.5 for 15 kHz radios.

5.3.5 CRYSTAL FILTERS

The 21.45 MHz IF signal is provided to the crystal filters Z221/Z222.

START

MEASURE CURRENT

YES

REFER TO SECTION 5.3.2

CHECK FUSES AND

WIRE HARNESS CONNECTIONS

REFER TO SECTION 5.3

AND VOLTAGES

CHECK DATA

OUTPUT

REFER TO SECTION 5.3.2

CHECK

CHECK AUDIO

YES

CHECK MIXER/

DETECT CIRCUIT

U241

CIRCUIT

REFER TO SECTION 5.3.4

REFER TO SECTION 5.3.3

REPLACE DEFECTIVE

COMPONENT

REFER TO SECTION 5.3.5

CHECK BUFFERS

CRYSTAL FILTERS

REPAIR DEFECTIVE

STAGE

CHECK RF AMP

FIRST MIXER

REFER TO SECTION 5.3.6