SERVICE MANUAL
LBB 3310/00, 3330/00 and 3331/00 page: 13 Date of issue:
4822 861 11006 July 1998
10.2 Measuring Instructions for the CPSU (LBB3310/00)
Introduction
The measurement procedure contains the following items:
• the internal supply voltages
• the supply current
• the audio-contribution to loudspeaker circuit
• the line-in to telephone-out, line-out and insertion-out circuit
• the rec-in to rec-out circuit
• the telephone-in to line-out circuit
• the mode switch (S240)
Use the diagrams in appendix A to located the measurement pads and components mentioned in the measurement
instructions.
10.2.1 Settings before you start measuring
• Set the insertion switch (S160), located at the rear side, to the left position (“1”).
• Set the potentiometer of the headphone volume (R254) to maximum (fully clockwise).
• Set the mode switch (S240) to “auto mode 1” (fully counterclockwise).
• Set the Volume control for the Delegate and Chairman units to maximum (fully clockwise).
• Set the gain control potentiometer (R140) for the external microphone in the middle position.
• Set the gain control potentiometer (R125) for the recorder input in the middle position.
10.2.2 Internal Supply Voltages
Connect the CPSU to the mains and measure the following internal supply lines, related to M2 (= GND):
M6 (V+) +19.5 V +/- 400 mV
M7 (V-) - 4.5 V +/- 100 mV
M15 +15 V +/- 750 mV
M25 +5 V +/- 250 mV
M26 +7.5 V +/- 350 mV
M27 +10 V +/- 500 mV
10.2.3 Phantom supply of the external symmetrical microphone input
Measure the following internal supply lines, related to M133 (= GND):
M28 +12 V +/- 600 mV
M131 +12 V +/- 600 mV
M132 +12 V +/- 600 mV
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