User's Manual

ManualsBrandsRELM WIRELESS CORP. - BK RADIO ManualsElectronicsVHF Mobile Transceiver

BK RADIO

Page 5-1

SECTION V

MAINTENANCE

5.1 INTRODUCTION

This section contains test and alignment procedures for an operational GMH Series mobile radio. This

section also contains disassembly and alignment procedures. An understanding of the theory of operation

is recommended before maintenance is attempted.

5.1.1 Test Equipment Required

RF Signal Generator HP8640 or equivalent

Distortion Analyzer HP334A or equivalent

Power Meter HP435B with 30 dB pad or equivalent

Service Monitor Cushman 4000 Radio Communications Test Set or equivalent

Digital Multimeter IBM PC or equivalent, with 256K memory and an RS-232 serial port

LAA0705 or LAA 0725 programming cable

GMH Editor Software

GMH Tool/Cable Kit LAA 0621, P/N 050-03152-0000

This tool kit consists of the following parts:

Heatsink 076-01475-0000

Spanner Tool 076-01451-0000

GMH RF Test Cable 155-02773-0000

2 X 6 Test Cable 155-02705-0000

Flex Cables (2 included) 155-02705-0000

2 X 5 Test Cable (2 included) 155-02622-0000

Audio Cable 155-02269-0000

5.2 OVERHAUL

5.2.1 Visual Inspection

This section contains instructions to assist in determining, by inspection, the condition of GMH assemblies.

Defects resulting from wear, physical damage, deterioration, or other causes can be found by these

inspection procedures. To aid inspection, detailed procedures are arranged in alphabetical order.

5.2.1.1 Capacitors, Fixed

Inspect capacitors for case damage, body damage, and cracked, broken, or charred insulation. Check for

loose, broken, or corroded terminal studs, lugs, or leads. Inspect for loose, broken, or improperly soldered

connections. On chip caps be especially alert for hairline cracks in the body and broken terminations.

Summary of content (13 pages)

PAGE 1
SECTION V M AINTENANCE 5.1 INTRODUCTION This section contains test and alignment procedures for an operational GMH Series mobile radio. This section also contains disassembly and alignment procedures. An understanding of the theory of operation is recommended before maintenance is attempted. 5.1.
PAGE 2
Maintenance GMH Series VHF Radio 5.2.1.2 Capacitors, Variable Inspect trimmers for chipped and cracked bodies, damaged dielectrics, and damaged contacts. 5.2.1.3 Chassis Inspect the chassis for deformation, dents, punctures, badly worn surfaces, damaged connectors, damaged fastener devices, loose or missing hardware, component corrosion, and damage to the finish. 5.2.1.4 Connectors Inspect connectors for broken parts and other irregularities.
PAGE 3
GMH Series VHF Radio Maintenance 4. Inspect for corrosion at the terminal. 5.2.2 Cleaning A. Using a clean, lint-free cloth lightly moistened with soap and water only, remove the foreign matter from the equipment case and unit front panel. Wipe dry using a clean, dry, lint-free cloth. B. Using a hand controlled dry air jet (not more than 15psi), blow the dust from inaccessible areas. Care should be taken to prevent damage by the air blast. C.
PAGE 4
Maintenance • 5.3.1 GMH Series VHF Radio VCO Board PA Flex Circuit PA Assembly (in the heatsink casting) Filter Board PA Board Accessory Board Unit Disassembly 1. Remove the four corner screws from the back of the heatsink casting. 2. Carefully pull the heatsink casting from the core assembly. 3. Disconnect the two flex cables and two coaxial cables from the PA board. NOTE: The black-end coax is the RX input to the receiver. The white-end coax is the exciter input to the PA. 4.
PAGE 5
GMH Series VHF Radio Maintenance 5.3.2.2 Display Board 1. Remove the Control board. 2. Remove the flat spring clip by prying the end with the tab toward the top of the housing. 3. Lift out the Display board. NOTE: During reassembly, check that the flex cable does not block the display by folding between the display and window. 5.3.2.3 Pushbutton Labels 1. 2. 3. 4. Pull out a pushbutton from the front of the radio. Remove the old label by pushing from the back. Insert the new label.
PAGE 6
Maintenance GMH Series VHF Radio 2. Remove the 3 screws from the System board. 3. Disconnect the front flex cable. 4. Lift out the System Board by lifting the front of the board first, then pulling the back flex through the casting. 5.3.3.4 System Board Reassembly 1. Insert the System board in the housing, carefully threading the back flex through the casting. 2. Attach the Synthesizer cover with the 4 screws. Insure that the rubber tubing is in the cavity above the large rectangular capacitor C119.
PAGE 7
GMH Series VHF Radio 5.5 Maintenance ALIGNM ENT PROCEDURES The GMH radio uses all electronic tuning with no manual adjustments. Use the GMH Editor computer software when alignment or adjustment is required. You will need an IBM or compatible computer with a disk drive, an RS-232 serial port, and DOS 3.3 or later. You will also need the GMH Editor software diskette (LAA0737) and an RS-232 interface cable (LAA0725), available from BK Radio.
PAGE 8
Maintenance GMH Series VHF Radio From the Edit Screen, press F6 (Menu). Press the down arrow key to select "Tune Radio" then press Enter. The program reads the EEPROM map of the core microprocessor Ii (system board). This takes about 5 seconds, during which the radio displays PROG. 5.5.4 SYNTHESIZER CALIBRATION Select "Synthesizer Calibrations" from the "Tune GMH" menu then press Enter. The radio will automatically perform any necessary adjustment.
PAGE 9
GMH Series VHF Radio Maintenance Connect a suitable 50~ power meter to the antenna output of the radio. Select "Transmitter power" from the "Tune GMH" menu and press Enter. Select "Start Transmit Power Test" and press Enter. "OK to Transmit?" appears in the lower left corner of the computer screen. Press Y to transmit. You can only adjust transmit power settings while transmitting.
PAGE 10
Maintenance 5.5.8 GMH Series VHF Radio DEVIATION ADJUST Connect a suitable attenuator and service monitor to the antenna output of the radio. Connect the modulation output of the service monitor to the Mic High input of the radio. Adjust the service monitor modulation output to a level of 0.15 VRMS and a frequency of I KHz. Select "Deviation Adjust" from the "Tune GMH" menu and press Enter. Insure that "Start Deviation Adjustment" is highlighted and press Enter.
PAGE 11
GMH Series VHF Radio Maintenance Unlike normal voice and audible tones, the low frequency signals present in Digital Code Guard cannot be applied as VCO modulation only. They must be presented to the reference oscillator using the DIA network RN1 and varactors CR102 and CR103 (system ). The subaudible information passes through the core microprocessor Ii (system board) where the variable attenuation is effected by software.
PAGE 12
Maintenance GMH Series VHF Radio Four varactors are used in the receiver front end bandpass filter. The control voltages for these varactors change to accommodate different receiver frequencies. The proper values are determined by microprocessor Ii (system board) using data stored in non-volatile memory. All four varactors share a common tuning voltage generated by DIA network I3 and RNA (RX/TX board).
PAGE 13
GMH Series VHF Radio Maintenance The GMH is designed to turn the audio on at approximately a 12 dB SINAD level and off at about a 6 dB level. If components in the IF filter or squelch filter are replaced, adjustment of the squelch levels may be necessary. The "Discriminator Audio Level", "Receiver Front End Tuning", and "Second Local Oscillator Frequency" adjustments must be correct before performing the Squelch adjustment.