Motorola Gm Series Detailed 6864115b62 B Manual
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VHF (136-174MHz) Transmitter Power Amplifier (PA) 45 W 2-11 5.6 Antenna Switch The antenna switch consists of two PIN diodes, D3471 and D3472. In the receive mode, both diodes are off. Signals applied at the antenna jack J3401 are routed, via the harmonic filter, through network L3472, C3474 and C3475, to the receiver input. In the transmit mode, K9V1 turns on Q3471 which enables current sink Q3472, set to 96 mA by R3473 and VR3471. This completes a DC path from PASUPVLTG, through L3473, D3471, L3477, L3472, D3472, L3471, R3474 and the current sink, to ground. Both diodes are forward biased into conduction. The transmitter RF from the directional coupler is routed via D3471 to the harmonic filter and antenna jack. D3472 also conducts, shunting RF power and preventing it from reaching the receiver port (RXIN). L3472 is selected to appear as a broadband lambda/4 wave transmission line, making the short circuit presented by D3472 appear as an open circuit at the junction of D3472 and the receiver path. 5.7 Harmonic Filter Components L3491-L3494 and C3489-C3498 form a nine-pole Chebychev low-pass filter to attenuate harmonic energy of the transmitter to specifications level. R3490 is used to drain electrostatic charge that might otherwise build up on the antenna. The harmonic filter also prevents high level RF signals above the receiver passband from reaching the receiver circuits, improving spurious response rejection. 5.8 Power Control The transmitter uses the Power Control IC (PCIC, U3501) to control the power output of the radio. A portion of the forward and reflected RF power from the transmitter is sampled by the directional coupler, rectified and summed, to provide a DC voltage to the RFIN port of the PCIC (pin 1) which is proportional to the sampled RF power. The ASFIC contains a digital to analog converter (DAC) which provides a reference voltage of the control loop to the PCIC via R3517. The reference voltage level is programmable through the SPI line of the PCIC. This reference voltage is proportional to the desired power setting of the transmitter, and is factory programmed at several points across the frequency range of the transmitter to offset frequency response variations of the transmitter’s power detector circuitry. The PCIC provides a DC output voltage at pin 4 (INT) which is amplified and shifted in DC level by stages Q3501 and Q3502. The 0 to 4 volt DC range at pin 4 of U3501 is translated to a 0 to 8.5 volt DC range at the output of Q3501, and applied as VCONT to the power-adjust input pin of the first transmitter stage U3401. This adjusts the transmitter power output to the intended value. Variations in forward or reflected transmitter power cause the DC voltage at pin 1 to change, and the PCIC adjusts the control voltage above or below its nominal value to raise or lower output power. Capacitors C3502-4, in conjunction with resistors and integrators within the PCIC, control the transmitter power-rise (key-up) and power-decay (de-key) characteristic to minimize splatter into adjacent channels. U3502 is a temperature-sensing device, which monitors the circuit board temperature in the vicinity of the transmitter driver and final devices, and provides a dc voltage to the PCIC (TEMP, pin 29) proportional to temperature. If the DC voltage produced exceeds the set threshold in the PCIC, the transmitter output power will be reduced so as to reduce the transmitter temperature.
Chapter 3 TROUBLESHOOTING CHARTS 1.0 Troubleshooting Flow Chart for Receiver (Sheet 1 of 2) Bad SINAD Bad 20dB Quieting No Recovered AudioSTART Audio at pin 8 of U3101 ?Check Controller (in the case of no audio) OR ELSE go to “B” Ye s No Spray or inject 44.85MHz into XTAL Filter FL3101 Audio heard ?BYe s No Check 2nd LO (44.395MHz) at C3135 LO present ?BYe s Check voltages on U3101Biasing OK ? No No A Ye s Check Q3102 bias for faults Replace Q3102 Go to B Ye s No Check circuitry around U3101. Replace U3101 if defectCheck circuitry around Y3101 Re- place Y3101 if defectVoltages OK?
3-2TROUBLESHOOTING CHARTS 1.1Troubleshooting Flow Chart for Receiver (Sheet 2 of 2) IF Signal at C3035? No RF Signal at T3001? RF Signal at C3012? No RF Signal at C3008? No RF Signal at C3474? No or Check Harmonic Filter J3401 and Antenna Switch D3471,D3472,L3472 Check filter between C3474 & C3008. Check tuning voltage at R3019 Inject RF into J3401 Is tuning voltage OK? No Ye s Check RF amp (Q3001) Stage Check filter between C3012 & T3001 Ye s Check T3001, T3002, D3031, R3030-R3034, L3032, C3034 and C3035 Ye s1st LO level OK? Locked? Ye s Check FGU Ye s Trace IF signal from C3035 to Q3101. Check for bad XTAL filter No Ye s IF signal at Q3102 collector? Before replacing U3101, check U3101 voltages Ye s Check for 5VDC Is 9V3 present? Check Supply Voltage circuitry. Check Q0681, U3211 and U0641 No No No Check U3501 Check varactor filter NoYe s Ye s Ye s A A B weak RF
Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3) 3-3 2.0 Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3) Current increase when keyed? NO YES START Check if Pressure Pad closes S3440 Check Components between Q3441 and RF Output, Antenna Switch D3471,D3472,Q3472 >500mA & 4A 1V Short TP3403 to Ground NO YES Voltage at TP3402 rises?Check PA StagesNO YES PCIC U3501 Pin 14 9.3V DC?Check 9.3 V Regulator U0641 NO YESPCIC U3501 Pin 16 >4V DCReplace PCIC U3501 NO YESTP3404 9.1V DC If U3201 Pin 2 is high, replace PCIC U3501,otherwise check controller and FGU YES NOTP3403 >0.5V DC?Replace PCIC U3501 Check Forward Power Sense Circuit (D3451) Check Forward Power Sense Circuit (D3451) NO YESPCIC U3501 Pin 5 > 1V DC? Check Power Setting, Tuning & Components between PCIC Pin 5 and ASFIC (U0221) Pin 4 before replacing ASFIC No or too low Power when keyed
3-4TROUBLESHOOTING CHARTS 2.1Troubleshooting Flow Chart for 25W Transmitter (Sheet 2 of 3) Check PA Stages No or too low Power when keyed Measure DC Voltage at Pin 2 & 3 of U3401>6 YESDC Voltage at U3501 Pin 23 =0? 2-6DC Voltage at U3402-1 Pin 1? YES Pin 2 Voltage 0.62 * Voltage at Pin 1? If U3201 Pin 2 is high, replace PCIC NOReplace U3401 YES NODC Voltage at U3402-1 Pin 3 = 8.8V? Check S3440, R3442 and R3443 YES Pin 3 Voltage 0.51 * Voltage at Pin 1? NOReplace U3401 6V Check Components between U3402-2 Pin7 and Q3421. Check Resistive Network at Pins 5 & 6 before repla- cing Q3421 YES DC Voltage at U3402-2 Pin 5
Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3) 3-5 2.2Troubleshooting Flow Chart for 25W Transmitter (Sheet 3 of 3) Check Final PA Stage NO 0V 1-4VBias 2 DC Voltage at TP3406? YESRF Voltage at TP3401 >100mV? YESRF Voltage U3401 Pin 6 >3V? Supply Replace Q3441 Check FGU (U3301) NOCheck Components between TP3401 & C3417 NO YESASFIC U0221 Pin 6 1-4V DC? Check Bias Tuning before replacing ASFIC U0221 Check Components between ASFIC and Q3441 before repla- cing Q3441 YESRF Voltage Q3421 Gate >1V? NOCheck Components between C3417 & Q3421 YESRF Voltage Q3441 Gate >4V? NOCheck Components between Q3421 & Q3441 Check Components between Q3441 & Antenna Connector Voltage
3-6TROUBLESHOOTING CHARTS 3.0 Troubleshooting Flow Chart for 45W Transmitter (Sheet 1 of 2) Current in- crease when keyed? NO YESSTART No or too low Power when keyed Check Components between Q3441 and RF Output, Antenna Switch D3471,D3472>500mA & 5A 1V >1V 4V DCReplace PCIC U3501 NO YESTP3404 9.1V DC If U3201 Pin 3 is high, replace PCIC U3501,otherwise check controller and FGU YES NO TP3403 >0.5V DC?Replace PCIC U3501Check Forward & Reverse Power Sense Circuitry (D3451 & D3452) Check Forward & Reverse Power Sense Circuitry (D3451 & D3452) NO YESPCIC U3501 Pin 5 > 1V DC? Check Power Setting, Tuning & Components between PCIC Pin 5 and ASFIC (U0221) Pin 4 before replacing ASFIC
Troubleshooting Flow Chart for 45W Transmitter (Sheet 1 of 2) 3-7 3.1Troubleshooting Flow Chart for Transmitter (Sheet 2 of 2) Pin 2 Voltage 0.62 * Voltage at Pin 1? NO YES Check PA Stages No or too low Power when keyed NOYES Replace U3401 Pin 3 Voltage 0.51 * Voltage at Pin 1? 2-4VSupply 0V Bias 1 DC Voltage at TP3406? NO YES PCIC U3501 Pin 24 2-4V DC? Check Bias Tuning be- fore replacing PCIC U3501 Check Voltage at Pin 2 & 3 of U3401 Replace U3401 Replace Q3421 NO 0V 1-4VBias 2 DC Voltage at TP3407? YESRF Voltage at TP3401 >100mV? YESRF Voltage U3401 Pin 6 >3V? Replace Q3421Supply Replace Q3431 Check FGU (U3301) NOCheck Components between TP3401 & C3417 NO YESASFIC U0221 Pin 6 1-4V DC? Check Bias Tuning be- fore replacing ASFIC U0221 Check Components between ASFIC and Q3431 before re- placing Q3431 YESRF Voltage Q3421 Gate >1V? NOCheck Components between C3417 & Q3421 YES RF Voltage Q3431 Gate >4V?NOCheck Components between Q3421 & Q3431YESRF Voltage Q3441 Base >5V? Check Components between Q3431 & Q3441NO Check Components between Q3441 & An- tenna Connector VoltageVoltage
3-8TROUBLESHOOTING CHARTS 4.0 Troubleshooting Flow Chart for Synthesizer +5V at U3201 Pin’s 13 & 30? 5V at pin 6 of D3201 Is information from µP U0101 correct? Is U3201 Pin 47 = 13VDC ? Is U3301 Pin 19 4.5 VDC in TX? (at VCO section) Start Visual check of the Board OK?Correct Problem Check 5V Regulator U3211 Is 16.8MHz Signal at U3201 Pin 19? Check Y3261, Y3263 and associated Parts Are signals at Pin’s 14 & 15 of U3201? Check R3201 Check C3319Is U3201 pin 2 >4.5 VDC in Tx &