µPC1876

22

Data Sheet S11666EJ4V0DS00

5.

ADJUSTMENT PROCEDURE

Precise alignment of the dbx decoder is absolutely critical for optimum performance. Where possible, the alignment

should be performed after the

µPC1876 is mounted in the chassis and with the video system active.

5.1

Stereo VCO Adjustment

Perform this adjustment with no signal applied.

(2) Measure the frequency of the STEREO LED DRIVER/STEREO VCO FREE-RUN MONITOR pin with a frequency

counter, and adjust the variable resistor connected to the STEREO VCO SETTING pin for a measured frequency

of 15.734 kHz

±50 Hz.

(3) Set the STEREO VCO FREE-RUN MONITOR SWITCH pin unconnected.

5.2

Filter Adjustment

Perform this adjustment with the MATRIX MUTE pin “L” and the STEREO VCO FREE-RUN MONITOR SWITCH

pin unconnected.

(1) Short the capacitor across the PILOT DISCRIMINATION FILTER (PD1 and PD2) pins by connecting these pins

together directly.

(3) Adjust the variable resistor connected to the FILTER ADJUSTMENT pin so that the AC output level at the RMS

OFFSET ABSORPTION pin is minimized. This signal is best monitored through a band-pass filter (15.734 kHz).

A recommended circuit is shown in 7. MEASURING CIRCUIT.

(4) Disconnect the short circuit across the PILOT DISCRIMINATION FILTER (PD1 and PD2) pins after adjustment.

5.3

Separation Adjustment

Perform this adjustment with the MATRIX MUTE pin “L”, the STEREO VCO FREE-RUN MONITOR SWITCH pin

unconnected, and the F-MONAURAL SELECTION pin “H”.

Verify that a L+R signal (100% modulation, 300 Hz, without noise reduction, pilot signal off) results in approximately

at the COMPOSITE SIGNAL INPUT pin.

(1) Apply a composite signal (30% modulation, 300 Hz, L-only, with noise reduction) to the COMPOSITE SIGNAL

INPUT pin.

(2) Adjust the variable resistor connected to the WIDE-BAND RMS SETTING pin so that the output at the R CHANNEL

OUTPUT pin is minimized.

(3) Apply a composite signal (30% modulation, 3 kHz, L-only, with noise reduction) to the COMPOSITE SIGNAL

INPUT pin.

(4) Adjust the variable resistor connected to the SPECTRAL RMS SETTING pin so that the output at the R CHANNEL

OUTPUT pin is minimized.

(5) Repeat steps (1) and (2).

Caution Be sure to perform step (5).