Motorola Mtx Series Detailed Rev 6881088c46 E Manual
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FMR-2045A-2December 26, 2003 UHF Band 2 Troubleshooting Charts: Troubleshooting Flow Chart for Controller 61 Chapter 6 UHF Band 2 Troubleshooting Charts 6.1 Troubleshooting Flow Chart for Controller MCU Check Power Up Alert Tone OK? Speaker OK? U409 EXTAL= 7.3728 MHz? U201 Pin 19 16.8 MHz 5V at U247? 3.3V at U248? U409 Reset Pin 94 High? MCU is OK Not able to pro- gram RF Board ICsBefore replacing MCU, check SPI clock, SPI data, and RF IC select Replace Speaker Read Radio OK? Check Setup Reprogram the correct data. See FGU Troubleshooting 7.5V at Pin 3/5 U247? 4/3.3V at Pin 1 U248Check Q400 Replace U247/U248 Check any short to SWB+, Vdda or Vddd Press PTT. Red LED does not light up PTT U409 Pin 53 low? Press PTT Q502-2 High? Check PB504 Check Q502-2 voltage LED Q502,R501 OK? Replace Faulty Component Check Accessories J403 OPT_SEL_1 & OPT_SEL_2 Pin 8 & 9 low? Radio could not PTT externally U409 Pin 52, 6 low? See FGU Troubleshoot- ing chart LED should light up Check MCU PTT NO YES YES No No NO YESYES NOYESYES NO NO YES YES NO NO YES NO YES NO YESYESNO NO YES EXT SPKR EXT PTT INT AUDIO J403 Pin 9 low? Pin 8 high? ASFIC U404 Pin 14 & 15 high? Check Accessories Check U404 Check U420 Audio PA NO NO YES YES J403 Audio at Pin 2 & Pin 3 Check Spk. Flex Connection Audio at AudioPA (U420) input (U447) Audio from Pin 41 ASFIC, U404? Check ASFIC U404 Check Audio PA (U420) Check U301 IF ICAudio at Pin 2 U404? NO NO NO YESYES NO YES
December 26, 2003FMR-2045A-2 62UHF Band 2 Troubleshooting Charts: Troubleshooting Flow Chart for Receiver (Sheet 1 of 2) 6.2 Troubleshooting Flow Chart for Receiver (Sheet 1 of 2) Bad SINAD Bad 20dB Quieting No Recovered AudioSTART Audio at pin 8 of U301?Check ControllerYe s No Spray or inject 1st IF 44.85 MHz into XTAL Filter Audio heard?BYe s No Check 2nd LO signal 44.395 MHz at C367 Signal Present?BYe s Voltages ok? Biasing ok? Check circuitry around U301. Replace U301 if defect No No A Ye sCheck Q302 bias circuitry for faults. Rotate Freq. Knob Replace Q302. Go to B Ye s No Check voltages on U301 Check circuitry around Y300. Replace Y300 if defect
FMR-2045A-2December 26, 2003 UHF Band 2 Troubleshooting Charts: Troubleshooting Flow Chart for Receiver (Sheet 2 of 2) 63 6.3 Troubleshooting Flow Chart for Receiver (Sheet 2 of 2) IF Signal at L311? No RF Signal at T301? RF Signal at C310? No RF Signal at C307? No RF Signal at C301? No or Check harmonic filters L101 & L102 and ant. switches CR101, CR102, L104 Check filter between C301 & C307; program filter to schematic test freq and check varactor voltages. Inject RF into J101 Are varactor voltages OK? No Ye s Check RF amp (Q301) Stage. Check filter between C310 & T301. Ye s Check T301, T302, CR306, R308, R309 Ye s 1st LO O/P OK? Locked?Ye s Check FGU Ye s Trace IF signal from L311 to Q302. Check for bad XTAL filter. No Ye sQ302 collec- tor OK? IF signal present? Before replacing U301, check U301 voltages; trace IF signal path. Ye s Check for 3.0 VDC Is R5 present? Check Q210, U201 (pin 48) voltages and U247 No No No Check U404 voltage. U404 can be selected by MCU before replacing U404. Check varactor filter. NoYe s Ye s Ye s A A B weak RF
December 26, 2003FMR-2045A-2 64UHF Band 2 Troubleshooting Charts: Troubleshooting Flow Chart for Transmitter 6.4 Troubleshooting Flow Chart for Transmitter START No Power Is There B+ Bias for Ant switchC h e c k Q 111 Is Current OK?Is Control Volt- age High or LowCheck PCIC 1. Check Pin Diodes 2. Check Harmonic Filter Inspect/Repair Tx. Output Network Is Power OK? Done Check Drive to Module Is Drive OK? Troubleshoot VCO Inspect PA Network/ Check Power Out of U101 at Cap C160 Is Power OK? Replace U101 Is Power OK? Replace Q101 Done Done No Ye s Ye sNo No Ye sLow High No Ye s Ye s No Ye s No
FMR-2045A-2December 26, 2003 UHF Band 2 Troubleshooting Charts: Troubleshooting Flow Chart for Synthesizer 65 6.5 Troubleshooting Flow Chart for Synthesizer 5V at pin 6 of CR201 Is information from µP U409 correct? Is U201 Pin 18 AT 4.54 VDC? Is U201 Pin 47 AT = 13 VDC Is U241 Pin 19 4.3 VDC in TX? Start Vi s u a l check of the Board OK?Correct Problem Check 5V Regulator +5V at U201 Pin’s 13 & 30? Is 16.8MHz Signal at U201 Pin 19? Check FL201, C206, C207, C208, CR203 & R204 Are signals at Pin’s 14 & 15 of U201? Check L202Check Q260, Q261 & R260 U201 pin 2 at >3V in Tx and -30 dBm? Are R231,R232, R233,C231,C232, & C233 OK? Replace U201 If L261, C263 & C264 are OK, then see VCO troubleshooting chart Are Waveforms at Pins 14 & 15 triangular? Do Pins 7,8 & 9 of U201 toggle when channel is changed? Check programming lines between U409 and U201 Pins 7,8 & 9 Replace U201 Check uP U409 Troubleshooting Chart NO YES NO YES NO YES NO YESNO NO NO YES YESNOYES YESNO YES YES YES NONO NO NO YES NO YES YESCheck CR201, U210, U211, C258, C259 & C228 3.3V at U201 pins 5, 20, 34 & 36Check U248, L201 & L202 Is 16.8MHz signal at U201 pin 23? Replace U201 YES NO NO YES NO YES
December 26, 2003FMR-2045A-2 66UHF Band 2 Troubleshooting Charts: Troubleshooting Flow Chart for VCO 6.6 Troubleshooting Flow Chart for VCO START No LO? Tx Carrier? VCO OK Check R260 TRB = 5V?Pin 10 >1V? L253 O/C?Change L253 Change U241 AUX 3 High? Check U201 Pin 2 for 3.2V Pin 19 =0V AUX 4 High? Change Q261 V ctrl 0V or 13V? L243 Open Circuit? Change U241 Change L243 Change U201 Check for faulty parts or dry joints of L271, L273, C370, C386, R339 & L320 A A No No Ye s Ye s Ye s No NoYe sYe s Ye s No Ye sNoNoYe sYe s No No Check R245 for dry joint or faulty No
Chapter 7 VHF Theory of Operation 7.1 Transmitter Figure 7-1. Transmitter Block Diagram 7.1.1 General (Refer to Figure 7-1.) The VHF transmitter contains five basic circuits: Power amplifier Antenna switch Harmonic filter Antenna matching network Power control integrated circuit (PCIC) 7.1.2 Power Amplifier The power amplifier consists of two devices: 9Z67 LDMOS driver IC (U3501) PRF1507 LDMOS PA (Q3501) The 9Z67 LDMOS driver IC contains a two-stage amplification with a supply voltage of 7.3V. This RF power amplifier is capable of supplying an output power of 0.3W (pin 6 and 7) with an input signal of 2mW (3 dBm) (pin16). The current drain would typically be 130mA while operating in the frequency range of 136-174 MHz. The PRF1507 LDMOS PA is capable of supplying an output power of 7W with an input signal of 0.3W. The current drain would typically be 1800 mA while operating in the frequency range of 136-174 MHz. The power output can be varied by changing the biasing voltage.PCIC Antenna PA Driver VcontrolVcontrol From VCO Jack Antenna Switch/ Harmonic Filter/ Matching Network PA Final Stage
December 26, 2003FMR-2045A-2 68VHF Theory of Operation: Transmitter 7.1.3 Antenna Switch The antenna switch circuit consists of two PIN diodes (D3521 and D3551), a pi network (C3531, L3551 and C3550), and three current limiting resistors (R3571, R3572, R3573). In the transmit mode, B+ at PCIC (U3502) pin 23 will go low and turn on Q3561 where a B+ bias is applied to the antenna switch circuit to bias the diodes “on.” The shunt diode (D3551) shorts out the receiver port, and the pi network, which operates as a quarter wave transmission line, transforms the low impedance of the shunt diode to a high impedance at the input of the harmonic filter. In the receive mode, the diodes are both off, and hence, there exists a low attenuation path between the antenna and receiver ports. 7.1.4 Harmonic Filter The harmonic filter consists of C3532 to C3536, L3531 and L3532. This network forms a low-pass filter to attenuate harmonic energy of the transmitter to specifications level. The harmonic filter insertion loss should be less than 1.2 dB. 7.1.5 Antenna Matching Network A matching network which is made up of L3538 and C3537 is used to match the antennas impedance to the harmonic filter. This will optimize the performance of the transmitter and receiver into an antenna. 7.1.6 Power Control Integrated Circuit (PCIC) The transmitter uses the Power Control IC (PCIC), U3502 to control the power output of the radio by maintaining the radio current drain. The current to the final stage of the power module is supplied through R3519 (0.1ohms), which provides a voltage proportional to the current drain. This voltage is then fed back to the Automatic Level Control (ALC) within the PCIC to keep the whole loop stable. The PCIC has internal digital to analog converters (DACs) which provide the reference voltage of the control loop. The voltage level is controlled by the microprocessor through the data line of the PCIC. There are resistors and integrators within the PCIC, and external capacitors (C3562, C3563 and C3565) in controlling the transmitter rising and falling time. These are necessary in reducing the power splatter into adjacent channels. U3503 and its associated circuitry acts as a temperature cut back circuitry. This circuitry provides the necessary voltage to the PCIC to cut the transmitter power when the radio temperature gets too high.
FMR-2045A-2December 26, 2003 VHF Theory of Operation: Receiver69 7.2 Receiver Figure 7-2. VHF Receiver Block Diagram 7.2.1 Receiver Front-End (Refer toVHF Receiver Front-End Schematic Diagram on page 80, VHF Receiver Back-End Schematic Diagram on page 81, and VHF Transmitter Schematic Diagram on page 84.) The RF signal is received by the antenna and applied to a low-pass filter. For VHF, the filter consists of L3531, L3532, C3532 to C3563. The filtered RF signal is passed through the antenna switch. The antenna switch circuit consists of two PIN diodes (D3521 and D3551) and a pi network (C3531, L3551 and C3550).The signal is then applied to a varactor tuned bandpass filter. The VHF bandpass filter comprises of L3301, L3303, C3301 to C3304 and D3301. The bandpass filter is tuned by applying a control voltage to the varactor diode (D3301) in the filter. The bandpass filter is electronically tuned by the DACRx from IC404 which is controlled by the microprocessor. Depending on the carrier frequency, the DACRx will supply the tuned voltage to the varactor diodes in the filter. Wideband operation of the filter is achieved by shifting the bandpass filter across the band. The output of the bandpass filter is coupled to the RF amplifier transistor Q3302 via C3306. After being amplified by the RF amplifier, the RF signal is further filtered by a second varactor tuned bandpass filter, consisting of L3305, L3306, C3311 to C3314 and D3302. Both the pre and post-RF amplifier varactor tuned filters have similar responses. The 3 dB bandwidth of the filter is about 12 MHz. This enables the filters to be electronically controlled by using a single control voltage which is DACRx. Crystal Filter Mixer Va r a c t o r Tuned Filter RF Amp Va r a c t o r Tuned Filter Pin Diode Antenna Switch RF Jack Antenna Control Voltage from ASFICFirst LO from VCO Second LOIF Amp 455kHz Filter Switch 455kHz Filter 455kHz FilterSwitch Demodulator RSSI LimiterRecovered Audio BW SELU3220
December 26, 2003FMR-2045A-2 70VHF Theory of Operation: Receiver The output of the post-RF amplifier filter is connected to the passive double balanced mixer which consists of T3301, T3302 and CR3301. Matching of the filter to the mixer is provided by C3317, C3318 and L3308. After mixing with the first LO signal from the voltage controlled oscillator (VCO) using high side injection, the RF signal is down-converted to the 44.85 MHz IF signal. The IF signal coming out of the mixer is transferred to the crystal filter (Y3200) through a resistor pad (R3321 - R3323) and a diplexer (C3320 and L3309). Matching to the input of the crystal filter is provided by C3201 and L3200. The crystal filter provides the necessary selectivity and intermodulation protection. 7.2.2 Receiver Back-End (Refer to VHF Receiver Back-End Schematic Diagram on page 81.) The output of crystal filter Y3200 is matched to the input of IF amplifier transistor Q3200 by L3203. Voltage supply to the IF amplifier is taken from the receive 5 volts (R5). The IF amplifier Q3200 is actively biased by a collector base feedback provided by R3202 and R3203. The gain controlled IF amplifer provides a maximum gain of about 16dB. A dual hot carrier diode (CR3201) limits the filter output voltage swing to reduce overdrive effects at RF levels above -27dBm. The amplified IF signal is then coupled into U3220 (pin 1) via L3202, C3207, and C3200 which provides the matching for the IF amplifier and U3220. The IF signal applied to pin 1 of U3220 is amplified, down-converted, filtered, and demodulated, to produce the recovered audio at pin 7 of U3220. Within U3220, the first IF 44.85 MHz signal mixes with the 44.395 MHz second local oscillator (2nd LO) to produce the second IF signal at 455 kHz. The 2nd LO signal frequency is determined by crystal Y3201. The second IF signal (455 kHz) is then filtered by an external ceramic filter Y3205 before being amplified by the second IF amplifier within U3220. Again, the signal is filtered by a second external ceramic filter Y3203 or Y3204 depending on the selected channel spacing. Y3203 is used for 20/25 kHz channel spacing whereas Y3204, for 12.5 kHz channel spacing. The simple circuit consisting of U3221, CR3202, CR3203 and resistors R3209, R3212, R3211 and R3205 divert the second IF signal according to the BW_SEL line. The filtered output of the second IF signal is applied to the limiter input pin of U3220 (Pin 14). The IF IC (U3220) contains a quadrature detector using a ceramic phase-shift element (Y3202) to provide audio detection. Internal amplification provides an audio output level around 120mVrms (@60% deviation) from pin 8 of U3220. This demodulated audio is fed to the ASFIC_CMP IC (U404) in the controller section. The IF IC (U3220) also performs several other functions. It provides a received signal-strength indicator (RSSI) with a dynamic range of 70 dB. The RSSI is a dc voltage monitored by the microprocessor, and used as a peak indicator during the bench tuning of the receiver front-end varactor filter. 7.2.3 Automatic Gain Control Circuit (Refer to VHF Receiver Front-End Schematic Diagram on page 80 and VHF Receiver Back-End Schematic Diagram on page 81.) The front-end automatic gain control circuit provides automatic reduction of gain, of the front-end RF amplifier via feedback. This action is necessary to prevent overloading of back-end circuits. This is achieved by drawing some of the output power from the RF amplifier output. At high radio frequencies, capacitor C3327 provides the low impedance path to ground for this purpose. CR3302 is a PIN diode used for switching the path on or off. A certain amount of forward biasing current is needed to turn the PIN diode on. Transistor Q3301 provides this current.