Telex MCE325 - Manual (Page 44)

4-6 C S I - 2 0 0 U s e r I n s t r u c t i o n s
8 Repeat for channels 2 through 4 by activating the TALK buttons, connecting to the test points
and adjusting the potentiometers as indicated in Table 4.4.
True Sidetone Adjust
1 Configure the DYN MIC HEADSET jack for stereo mode (See Section 3, “MONO”)
2 Set all front panel buttons to off.
3 Connect 51 ohm load resistors across the left headphone output (J2 pins 3 and 4) and right
headphone output (J2 pins 3 and 5).
4 Connect an AC voltmeter across the left headphone output.
5 Remove the signal generator from the mic input, and connect it across intercom channel 1.
Adjust the generator output to –1 dBu (0.69 VAC), 1 kHz.
6 Activate the CH 1 TALK button, and adjust the CH 1-3 volume control (R1) until you measure
11.2 dBu (2.82 VAC) across the left headphone output.
7 Disconnect the signal generator from intercom channel 1. Adjust the generator for minimum
output, and reconnect it across the DYN MIC HEADSET jack mic input (J2 pins 1 & 2).
Readjust the generator output level to –45 dBu, 1 kHz.
8 Turn on the MIC ON button.
9 Adjust R37 (sidetone) on the MCE325 main board to obtain 8.7 dBu (2.1 VAC) at the left
headphone output.
Level and Frequency Response Check, Intercom Channel to
Headphone
1 Set all front panel buttons to off.
2 Remove the signal generator from the mic input, and reconnect it across intercom channel 1.
3 Adjust the signal generator output to –1 dBu, 1 kHz.
4 Preset the CH 1-3 volume control to the 2 o’clock position.
5 Activate the CH 1 TALK button. The left headphone output level should be 11.2 ±2 dBu (2.2
to 3.6 VAC).
6 Adjust the CH 1-3 volume control to measure 11.2 dBu (2.8 VAC) at the left headphone
output. Check for no distortion or clipping in the output.
7 Adjust the signal generator output to –1 dBu, 100 Hz. The left headphone output should read
10.2 dBu ±2 dBu (1.9 to 3.2 VAC)
8 Adjust the signal generator output to –1 dBu, 10 kHz. The left headphone output should read
7.8 dBu ±2 dBu (1.5 to 2.4 VAC).
9 Repeat the test for channels 2 through 4. For channel 3, continue to use the CH 1-3 volume
control and monitor the left headphone output. For channels 2 and 4, use the CH2-4 volume
control and monitor the right headphone output.
Table 4.4 Channel 1-4 sidetone trimmer adjust.
TALK BUTTON TEST POINT POTENTIOMETER
CH 1 U5 pin 7 R57 (Sidetone 1)
CH 2 U5 pin 1 R73 (Sidetone 2)
CH 3 U7 pin 1 R88 (Sidetone 3)
CH 4 U7 pin 7 R104 (Sidetone 4)