Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual
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Frequency Synthesis2-7
A voltage of 5V applied to the super filter input (U3201 pin 30) supplies an output voltage of 4.5 Vdc
(VSF) at pin 28. It supplies the VCO, VCO modulation bias circuit (via R3363) and the synthesizer
charge pump resistor network (R3251, R3252). The synthesizer supply voltage is provided by the 5V
regulator U3211.
In order to generate a high voltage to supply the phase detector (charge pump) output stage at pin
VCP (U3201-47), a voltage of 13 Vdc is being generated by the positive voltage multiplier circuits
(D3201, C3202, C3203). This voltage multiplier is basically a diode capacitor network driven by two
signals (1.05MHz) 180 degrees out of phase signals (U3201-14 and -15).
Output LOCK (U3201-4) provides information about the lock status of the synthesizer loop. A high
level at this output indicates a stable loop. IC U3201 provides the 16.8 MHz reference frequency at
pin 19.
The serial interface (SRL) is connected to the µP via the data line DATA (U3201-7), clock line CLK
(U3201-8), and chip enable line CSX (U3201-9).
4.3 Voltage Controlled Oscillator (VCO)
The Voltage Controlled Oscillator (VCO) consists of the VCO/Buffer IC (VCOBIC, U3301), the TX
and RX tank circuits, the external RX buffer stages, and the modulation circuits.
Figure 2-4 VHF VCO Block Diagram
Presc
RX
TXMatching
NetworkLow Pass
Filter
Attenuator Pin8
Pin14
Pin10(U3211 Pin1)
VCC Buffers
TX RF Injection U3201 Pin 32 AUX3 (U3201 Pin2)
Prescaler Out
Pin 12 Pin 19 Pin 20
TX/RX/BS
Switching Network
U3301
VCOBIC
Rx
Active Bias
Tx
Active Bias
Pin2
Rx-I adjustPin1
Tx-I adjustPins 9,11,17
Pin18Vsens
Circuit Pin15 Pin16 RX VCO
Circuit
TX VCO
Circuit RX Tank
TX TankPin7
Vcc-Superfilter
Collector/RF in
Pin4
Pin5
Pin6RX
TX
(U3201 Pin28)Rx-SW
Tx-SW
Vcc-Logic
(U3211 Pin1) Steer Line
Voltage
(VCTRL)Pin13
Pin3TRB IN
LO RF INJECTION
Q3304
Q3301
2-8Frequency Synthesis The VCOBIC together with the Fractional-N synthesizer (U3201) generates the required frequencies in both the transmit and receive modes. The TRB line (U3301, pin 19) determines which tank circuits and internal buffers are to be enabled. A high level on TRB enables the TX tank and TX output (pin 10), and a low enables the RX tank and RX output (pin 8). A sample of the signal from the enabled RF output is routed from U3301, pin 12 (PRESC_OUT), via a low pass filter, to U3201, pin 32 (PREIN). A steering line voltage (VCTRL) between 2.5 volts and 11 volts at varactor diode D3361 tune the full TX frequency range (TXINJ) from 136 MHz to 174 MHz, and varactor diode D3341 tunes the full RX frequency range (RXINJ) from 181 MHz to 219 MHz. The RX tank circuit uses a Hartley configuration for wider bandwidth. For the RX tank circuit, an external transistor Q3304 is used for better side-band noise. The external RX buffers (Q3301 and Q3302) are enabled by a high at U3301, pin 7 (RX_SWITCH) via transistor switch Q3303. In the TX mode, the modulation signal (VCOMOD) from the LVFRAC-N synthesizer IC (U3201 pin 41) is applied to varactor diode D3362, which modulates the TX VCO frequency via capacitor C3362. Varactor D3362 is biased for linearity from the VSF. 4.4 Synthesizer Operation The complete synthesizer subsystem consists of the low voltage FRAC-N (LVFRACN), reference oscillator (a crystal oscillator with temperature compensation), charge pump circuit, loop filter circuit and a dc supply. The output signal PRESC from the VCOBIC (U3301 pin 12) is fed to U3201 pin 32 (PREIN) via a low pass filter (C3318, L3318 and C3226) which attenuates harmonics and provides the correct level to close the synthesizer loop. The pre-scaler in the synthesizer (U3201) is a dual modulus type with selectable divider ratios. The divider ratio of the pre-scaler is controlled by the loop divider, which in turn receives its inputs via the SRL. The output of the pre-scaler is applied to the loop divider. The output of the loop divider is connected to the phase detector, which compares the loop divider´s output signal with the reference signal. The reference signal is generated by dividing down the signal of reference oscillator Y3261 or Y3262. The output signal of the phase detector is a pulsed dc signal which is routed to the charge pump. The charge pump outputs a current at U3201 pin 43 (IOUT). The loop filter (which consists of R3221- R3223 and C3221-C3224) transforms this current into a voltage that is applied to the varactor diodes (D3361 for transmit, D3341 for receive) to alter the output frequency of the appropriate VCO. The current can be set to a value fixed within the LVFRAC-N IC, or to a value determined by the currents flowing into BIAS 1 (U3201-40) or BIAS 2 (U3201-39). The currents are set by the value of R3251 and R3252 respectively. The selection of the three different bias sources is done by software programming. To reduce synthesizer lock time when new frequency data has been loaded into the synthesizer, the magnitude of the loop current is increased by enabling the IADAPT pin (U3201-45) for a certain software programmable time (adapt mode). The adapt mode timer is started by a low to high transient of the CSX line. When the synthesizer is within the lock range, the current is determined only by the resistors connected to BIAS 1 and BIAS 2, or by the internal current source. A settled synthesizer loop is indicated by a high level signal at U3201-4 (LOCK). The LOCK signal is routed to one of the µP´s ADC inputs (U0101-56). From the measured voltage, the µP determines whether LOCK is active. To modulate the PLL, the two spot modulation method is utilized. Via U3201, pin 10 (MODIN), the audio signal is applied to both the A/D converter (low frequency path) as well as the balance attenuator (high frequency path). The A/D converter changes the low frequency analog modulating signal into a digital code that is applied to the loop divider, thereby causing the carrier to deviate. The balance attenuator is used to adjust the VCO’s deviation sensitivity to high frequency modulating signals. The output of the balance attenuator is present at the MODOUT port (U3201-41) and connected to the VCO modulation diode D3362 via R3364.
3-1 Section 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 defect Check circuitry around Y3101. Replace Y3101 if defectVoltages OK?
3-2Troubleshooting Flow Chart for Receiver 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 45W Transmitter 3-3 2.0 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 AS- FIC
3-4 Troubleshooting Flow Chart for 45W Transmitter 2.1Troubleshooting Flow Chart for 45W 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 YES ASFIC 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 Vo ltag eVolta ge
Troubleshooting Flow Chart for Synthesizer3-5 3.0 Troubleshooting Flow Chart for Synthesizer +5V at U3201 Pins 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) Sta rt 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 Pins 14 & 15 of U3201? Check R3201 Check C3319Is U3201 pin 2 >4.5 VDC in Tx &
3-6Troubleshooting Flow Chart for VCO 4.0 Troubleshooting Flow Chart for VCO Are Q3301 Base at 0.7V Collector at 4.5V Emitter at 110mV Are Q3304 Base at 2.4V Collector at 4.5V Emitter at 1.7VAre U3301 Pins 13 at 4.4V 15 at 1.1V 10 at 4.5V 16 at 1.9V Low or no RF Signal at TP3001 Visual check of board OK? 35mV DC at U3301 Pin 19 NO YES at base of Q3301 NO NO NO NONO YES YES YES YESYESLow or no RF Signal at input to PA5V DC at U3301 Pin 14 & 18 OK ? 4.8V DC at U3301 Pin 19 Is RF available at TP3401 YES YESYESYES YES NO NO NO NO NO Audio =180mVrms at “-” side of D3362 2.5VDC at D3362 If C3362 and R3363 are OK, then replace D3362 Replace R3363 Replace R3364 NONO YES YES If R3402 and C3315 are OK, replace U3301 TX VCO RX VCO Correct ProblemVisual check of board OK? Make sure U3211 is working correctly and runner between U3211 Pin 1 and U3301 Pin 14 & 18 is OK Check runner between U3201 Pin 2 and U3301 Pin 19 Is RF available If all parts from U3301 Pin 8 to Base of Q3301 are OK, replace U3301 If all parts associated with the pins are OK, replace Q3301 Check parts between T3001 and Q3301Power OK but no modulation If all parts from TP3401 of U3401 Pin 16 are OK, replace U3401 If all parts associated with the pins are OK, replace U3301 4.5V DC at U3301 Pin 3 OK? YES NO4.5V DC at U3301 Pin 3 OK? YES NO Make sure Synthesizer is working correctly and runner between U3201 Pin 28 and U4301 Pin 3 is OK 5V DC at U3301 Pin 14 & 18 OK ? OK? OK? If all parts associated with the pins are OK, replace Q3301
4-1 Section 4 VHF PCB/SCHEMATICS/PARTS LIST 1.0 Allocation of Schematics and Circuit Boards 1.1 Controller Circuits The VHF circuits are contained on the Printed Circuit Board (PCB) which also contains the Controller circuits. This Chapter shows the schematics for the VHF circuits only, refer to the Controller section for details of the related Controller circuits . The PCB component layouts and the Parts Lists in this Chapter show both the Controller and VHF circuit components. The VHF schematics and the related PCB and parts list are shown in the tables below. Table 4-1 VHF 25-45W Diagrams and Parts Lists PCB : 8486140B13 Main Board Top Side 8486140B13 Main Board Bottom SidePage 4-3 Page 4-4 SCHEMATICS Power Amplifier 25 - 45W FRACN Voltage Controlled Oscillator Receiver Front End IF Page 4-5 Page 4-6 Page 4-7 Page 4-8 Page 4-9 Parts List 8486140B13 Page 4-10
4-2Allocation of Schematics and Circuit Boards THIS PAGE INTENTIONALLY LEFT BLANK