Amc XT tun service manual

Page 2

TUNER ALIGNMENT PROCEDURE
FM SECTION
A. PREPARATION

1.

2.
3.
4

Set stereo modulator to mono mode with 1KHZ modulating signal unless otherwise state.
Set signal generator to FM mode with 75KHz deviation.
Store the following frequencies: 875MHz, 90.1MHz, 98.1MHZ, 106.1MHz and 107.9MHZ.

. RF levels are open circuit voltages of signal generator with 75 ohms output impedance.

B. OSCILLATOR TUNING VOLTAGE

1.
2.
3.

Connect DVM between FE1 No. 5 PIN and ground.
Tune to 87.5MHz and check DVM for reading of 3Vdc +/-0.5Vdc
Tune to 107.9MHz and check DVM for reading of 20.5Vdc +/-0.5Vdc.

If either of the above is out of tolerance, adjust FE1 (oscillator coil L101) until both readings are

within tolerance.

C.I

.F.
1
2
3.
4
5

. Connect DVM between TP2 and TP3.
. Apply 98.1MHz (60dBu) to FM antenna input and tune to 98.1MHz.

Adjust IFTl (FM IF) for OVdc +/-50mV reading on DVM.

. Adjust IFT2 (FM IF) until minimum THD is achieved at audio output.

. Repeat (3) and (4) until no further improvement can be made.

D. FRONT-END IF.

1.
2.

E. R.F.

Apply 98.1MHz (12dBu) to antenna input and tune to 98.1MHZ.
Carefully adjust FE1 IFT until minimum THD is achieved at audio output.

1. Apply 98.1MHz (7dBu) to antenna input and tune to 98.1MHz.
2. Check if THD is better than 3%. If not, proceed to (3).
3. Adjust FRONT-END COILS (L102 - L104) by squeezing or stretching using a non-metallic

tool until THD is better than 3%.
Check THD at 90.1MHz and 106.1MHZ with 8dBu input. If THD is more than 3% for both

frequencies, re-adjust until required THD is met.

F. AUTOSEARCH AND FM STEREO LEVEL

1.
2.
3.

Turn VR2 fully clockwise.
Set stereo modulator to L=R mode and 98.1MHZ (32dB) to antenna input.
Adjust VR2 clockwise until S light up in the LCD.