Ericsson LBI-38505A manual Description, Maintenance, Disassembly

LBI-38505 LBI-38505

DESCRIPTION

MASTR II Base Station, 406 to 512 megahertz receivers are single conversion, superheterodyne FM receivers designed for one-through eight-frequency operation. The solid state receiver utilizes integrated circuits (ICs), monolithic crystal filters and discrete components with each of the crystal filters located between gain stages to provide 100 dB selectivity and maximum protection from de-sensitization and intermodula- tion.

The receiver consists of the following modules:

∙RF Assembly (Includes Mixer)

∙IF-Filter

∙Oscillator/Multiplier (Osc/Mult)

∙IF/Audio and Squelch (IFAS)

∙Optional Ultra-High Sensitivity (UHS) Pre-Amplifier

Audio, supply voltages and control functions are con- nected to the system board through P903 on the Osc/Mult board, and P904 on the IFAS board. The regulated +10 Volts is used for all receiver stages except the audio PA stage which operates from the A+ system supply.

Centralized metering jack J601 on the IFAS board is pro- vided for use with Test Set 4EX3A11 or Test Kit 4EX8K12. The test set meters the oscillator, multiplier, IF Detector and IF amplifier stages. Speaker high and low are metered on the system board metering jack.

A block diagram of the complete receiver is shown in Figure 2.

Refer to the appropriate Maintenance Manual for complete details on each receiver module listed in the Table of Contents.

MAINTENANCE

DISASSEMBLY

To service the Receiver from the top (see Mechanical Parts Breakdown):

1.Pull the locking handle down, then pry up the top cover at the front notch and lift off the cover.

To service the Receiver from the bottom:

1.Pull the locking handle down and pull the radio out of the mounting frame.

2.

Remove the top cover, then loosen the two bottom cover retaining screws and remove the bottom cover (see Fig- ure 1).

3.To gain access to the bottom of the Osc/Mult and IFAS board, remove the six screws (A) holding the receiver bottom cover (see Figure 3).

NOTE

Refer to Figure 4 for receiver module location.

To remove the OSC/Mult board from the radio:

1.Remove the six screws (A) holding the receiver bottom cover.

2.Remove the eight screws (E) holding the IF-Filter bottom cover.

3.Remove the four screws (B) holding the board.

4.Press straight down on the plug-in Osc/Mult board from the top to avoid bending the pins when unplugging the board from the system board jack.

To remove the IFAS board from the radio:

1.Remove the six screws (A) holding the bottom cover, and the one screw (C) holding the board.

2.Remove the two screws (D) holding the audio PA heatsink to the right side rail.

Figure 2 - Receiver Block Diagram

Figure 1 - Disassembly Procedure

(Top View)

2