Telex MCE325 - Manual (Page 43)

4-5
Two-Channel, Four-Wire Mode
1 Remove the 200 ohm terminations from intercom channels 1 through 4.
2 Program the MCE325 to be in two-channel, four-wire mode. (See Table 2.3, configuration 6
for switch settings. See Figure 1.11 for names of buttons in standard two-channel mode.)
3 Connect 200 ohm termination resistors across the four-wire A and four-wire B channels:
Four-Wire A: J8 pins 2 and 3
Four-Wire B: J10 pins 2 and 3
NOTE Normally, the four-wire outputs would be terminated with 600 ohms for four-wire operation,
but 200 ohms are used for testing purposes.
4 Set the MIC ON button to on. Set all other front panel buttons to off.
5 Connect an AC voltmeter across the Four-Wire A output.
6 The signal generator should still be connected to the mic input. Set it to 1 kHz, -45 dBu.
7 Activate CH 1 TALK.
8 The output level should read –0.8 dBu ±2 dBu (0.56 – 0.89 VAC)
9 Connect the AC voltmeter across the Four-Wire B output.
10 Turn off CH 1 TALK and activate CH 2 TALK.
11 The output level should read –0.8 dBu ±2 dBu (0.56 – 0.89 VAC)
12 Remove the 200 ohm termination resistors.
Sidetone Null Test and Adjustment
NOTE This procedure verifies sidetone null operation and optimizes nulling for an ideal 200 ohm line
termination. Since actual intercom line impedance may vary from the ideal, the MCE325 may
have to be readjusted slightly during actual use.
1 Reprogram the MCE325 to be in four-channel, two-wire mode (Table 2.3, configuration 2).
2 Reconnect 200 ohm termination resistors across each of the four intercom channels.
3 Set the MIC ON button to on. Set all other front panel buttons to off.
4 The signal generator should still be connected to the mic input. Set it to 1 kHz, -45 dBu.
5 Activate the CH 1 TALK button.
6 Monitor the AC signal level at U5 pin 7.
7 Adjust R57 (Sidetone 1 on front panel) for maximum null (minimum signal level) at U5 pin 7.
The signal should be 0.025 VAC or less.
10 kHz -55 dBu (1.4 mV)
–45 dBu (4.35 mV)
–25 dBu (43.5 mV) -5.7 ±3 dBu (0.28 – 0.57 VAC)
2.2 ±2 dBu (0.79 – 1.26 VAC)
2.5 ±2dBu (0.83 – 1.32 VAC)
Table 4.3 Mic to line response; 4-channel, 2-wire mode.
INPUT
FREQUENCY INPUT
LEVEL
OUTPUT LEVEL
1 kHz -45 dBu -0.8 ±2 dBu (0.56 – 0.89 VAC)
100 Hz -45 dBu -0.8 ±2 dBu (0.56 – 0.89 VAC)
100 kHz -45 dBu 0.8 ±2 dBu (0.56 – 0.89 VAC)
Table 4.2 USMB frequency response and level check.