Motorola Pr400 Detailed 6881096c25 B Manual
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6881096C25-BJune, 2005 146-174 MHz VHF Theory Of Operation: VHF Frequency Generation Circuitry 5-5 Transmit modulation from the ASFICcmp (U451 pin 40) is applied to U201 pin 10 (MOD_IN). An electronic attenuator in the ASFICcmp adjusts overall transmitter deviation by varying the audio level applied to the synthesizer IC. Internally the audio is digitized by the Fractional-N synthesizer and applied to the loop divider to provide the low-port modulation. The audio is also routed through an internal attenuator for the purpose of balancing the low port and high port modulation and reducing the deviation by 6 dB for 12.5 kHz channels, and is available at U201 pin 41 (VCO_MOD). This audio signal is routed to the VCOs modulator. Figure 5-3. VHF Frequency Generation Unit Block Diagram 5.4.1 Fractional-N Synthesizer The Fractional-N synthesizer, shown in Figure 5-4, uses a 16.8 MHz crystal (Y201) to provide the reference frequency for the system. External components C201-C203, R202 and D201 are also part of the temperature-compensated oscillator circuit. The dc voltage applied to varactor D201 from U201 pin 25 is determined by a temperature-compensation algorithm within U201, and is specific to each crystal Y201, based on a unique code assigned to the crystal that identifies its temperature characteristics. Stability is better than 2.5 ppm over temperatures of -30 to 60 °C. Software- programmable electronic frequency adjustment is achieved by an internal DAC which provides a frequency adjustment voltage from U201 pin 25 to varactor D201. The synthesizer IC U201 further divides the 16.8 MHz signal to 2.1 MHz, 2.225 MHz, or 2.4 MHz for use as reference frequencies. It also provides a buffered 16.8 MHz signal at U201 pin 19 for use by the ASFICcmp. To achieve fast locking of the synthesizer, an internal adapt charge pump provides higher current at U201 pin 45 to quickly force the synthesizer within lock range. The required frequency is then locked by the normal mode charge pump at pin 43. A loop filter (C243-C245 and R243-R245) removes noise and spurs from the steering voltage applied to the VCO varactors, with additional filtering located in the VCO circuit. Both the normal and adapt charge pumps get their supply from the capacitive voltage multiplier made up of C221-C224 and D220-D221. Two 3 V square waves from U201 pins 14-15 provide the drive signals for the voltage multiplier, which generates 12.1 V at U201 pin 47. This voltage is filtered by C225-C228. Synthesizer U201VCOBIC U251 Voltage Multiplier Loop Filter To Mixer To PA Driver VCP Vmult1 Vmult2Aux3 MOD Out Modulating SignalRx VCO Circuit Tx VCO Circuit TRB 16.8 MHz Ref. Osc. Rx Out Tx Out Buffer Q280
June, 20056881096C25-B 5-6146-174 MHz VHF Theory Of Operation: VHF Frequency Generation Circuitry One of the auxiliary outputs of the synthesizer IC (AUX3, U201 pin 2) provides the TRB signal which determines the operating mode of the VCO, either receive or transmit. Figure 5-4. VHF Synthesizer Block Diagram 5.4.2 Voltage Controlled Oscillator (VCO) The VCOBIC (U251), shown in Figure 5-5, in conjunction with the Fractional-N synthesizer (U201) generates RF in both the receive and the transmit modes of operation. The TRB line (U251 pin 19) determines which oscillator and buffer are enabled. A sample of the RF signal from the enabled oscillator is routed from U251 pin 12 through a low pass filter, to the prescaler input of the synthesizer IC (U201 pin 32). After frequency comparison in the synthesizer, a resultant DC control voltage is used to steer the VCO frequency. When the PLL is locked on frequency, this voltage can vary between 3 V and 9 V. L251 and C251 further attenuate noise and spurs on the steering line voltage. In the receive mode, the TRB line (U251 pin 19) is low. This activates the receive VCO and the receive buffer of U251, which operate within the range of 190.85 to 218.85 MHz. The VCO frequency is determined by tank inductor L254, C253-C257, and varactor D251. The buffered RF signal at U251 pin 8 is further amplified by Q280 and applied as RX_INJ to the low-pass injection filter in the receiver front end circuit. In the transmit mode, U251-19 is driven high by U201 pin 2, enabling the transmit VCO and buffer. The 146-174 MHz RF signal from U251 pin 10 is applied as TX_INJ to the input of the transmitter circuit via matching network C290-C291 and L291. TX VCO frequency is determined by L264, C263- DATA CLK CEX MODIN V CC, 5V XTAL1 WARP PREIN VCP Reference Oscillator Voltage Multiplier Voltage Controlled Oscillator 2-Pole Loop Filter DATA (U401 Pin 100) CLOCK (U401 Pin 1) SYNTH_CS (U401 Pin 47) MOD IN (U451 Pin 40) +5V (U310 Pin 5)7 8 9 10 13,30 23 25 32 47 VMULT2 VMULT1BIAS1 SFOUTAUX3 IADAPTIOUTGND FREFOUTLOCK4 19 6,22,23,24 43 45 2 28 141540Filtered 5VSteering Line LOCK (U401 Pin 56) Prescaler InLO RF Injection TX RF Injection (First Stage of PA) FREF (U451 Pin 34) 39 BIAS241 +3V (U330 Pin 5) V DD, 3VMODOUTU201 Low Voltage Fractional-N Synthesizer 5,20,34,36 TRB VCO Mod
6881096C25-BJune, 2005 146-174 MHz VHF Theory Of Operation: Keypad 5-7 C267, and varactor D261. High-port audio modulation from the synthesizer IC is applied as VCO_MOD to varactor D262 which modulates the transmit VCO. Figure 5-5. VHF VCO Block Diagram 5.5 Keypad The keypad block diagram is shown in Figure 5-6. Pressing a key creates two distinct voltages KEYPAD_ROW and KEYPAD_COL. These voltages are sent directly to the radio’s microprocessor on the main board. The microprocessor then interprets the voltage for KEYPAD_ROW and KEYPAD_COL for each key press. Figure 5-6. Keypad Block Diagram Presc RX TX Matching Network Pin 8 Pin 14 Pin 103V (U330 Pin 5) VCC BuffersU201 Pin 32 AUX3 (U201 Pin 2) Prescaler Out Pin 12 Pin 19 Pin 20 TX/RX/BS Switching Network U251 VCOBIC Rx Active Bias Tx Active Bias Pin 2 Rx-I adjustPin 1 Tx-I adjustPins 9,11,17 Pin 18Vsens Circuit Pin 15 Pin 16 TX VCO Circuit TX TankRX VCO Circuit RX TankPin 7 Vcc-Superfilter Collector/RF in Pin 4 Pin 5 Pin 6RX TX V_SF (U201 Pin 28)NC NC Vcc-Logic 3V (U330 Pin 5) Steer Line Voltage (V_STEER) Pin 13 Pin 3 TRB_IN Buffer Q280 RX INJ V_SF (U201 Pin 28) TX INJ Keypad ButtonMCP Keypad RowKeypad Row Keypad Row Keypad ColumnKeypad Column Keypad Column 28 Pin Connector (keypad Board) 28 Pin Connector (Main Board)
June, 20056881096C25-B 5-8146-174 MHz VHF Theory Of Operation: Keypad Notes:
Chapter 6 VHF Troubleshooting Tables 6.1 Troubleshooting Table for Receiver Table 6-1. Troubleshooting Table for Receiver Symptom Possible Causes Procedure Corrective Action Radio Dead (no turn-on beep, no LED indication)1. Battery dead or defec- tive.Substitute known good battery or battery eliminator.Charge or replace battery. 2. Defective battery con- tacts.Inspect battery contacts for corrosion or bent terminals.Clean/repair/replace J301. 3. Blown fuseCheck voltage on each side of fuse. If blown, 0 VDC after fuse.Check for short on output, check D301, VR301, trouble- shoot/repair as needed, replace fuse. 4. DC switching fault Verify battery voltage present at S444 pin 5 when radio is on. Verify Q494-1 is at least 1 V dc, Q494-6 is ~0.1 V dc, Q493-3 is at Vbatt.Check/replace on-off-volume control S444. Troubleshoot/replace Q493/4. 5. Microprocessor not starting up.Verify clock input to U401-90 (EXTAL) is 7.3975 MHz using high impedance probe. If clock is 3.8 MHz, check for shorts on U401 pins. Connect RIB to verify communica- tion via CPS. Verify U401-94 (RESET) is high.Verify 16.8 MHz signal at U451- 34. If OK, troubleshoot/replace U451. If not present, trouble- shoot U201 Synthesizer. Repro- gram/reflash as needed. If RESET is Low, troubleshoot regulator U320. Check for shorts at U401 pins. Replace U401 (depot only). Reprogram/ reflash as needed. 6. Regulator fault Verify U310-5 is 5 V dc, U320-5 is 3.3 V dc, U330-5 is 3 V dc.Check for shorts on outputs, troubleshoot/repair as needed, replace faulty regulator.
June, 20056881096C25-B 6-2VHF Troubleshooting Tables: Troubleshooting Table for Receiver No Audio 1. Synthesizer out of lockVerify U201-4 is at 3 V dc.Troubleshoot synthesizer/VCO circuits. 2. Defective IFIC Verify audio is present at U51-8. Check Q70, Y70, U51. 3. RX audio buffer faultVerify audio is present at U451-2.Check U510 and associated parts. 4. ASFIC fault Verify audio is present at U451-41. Verify U451-14 is high.Check squelch setting, PL/DPL programming. Troubleshoot/ replace U451. 5. Audio PA faultVerify U490-1 is
6881096C25-BJune, 2005 VHF Troubleshooting Tables: Troubleshooting Table for Synthesizer 6-3 6.2 Troubleshooting Table for Synthesizer Table 6-2. Troubleshooting Table for Synthesizer Symptom Possible Causes Procedure Corrective Action Synthesizer Out of Lock (RX mode only)1. VCO faultVerify oscillator is working, check RF level at U251-10 per schematic. Check dc voltages at U251 pin 2 through 6 and 10 per Table 6-4. Verify steering line voltage is between ~3 V and 10 V. Check VCO tank components connected to U251-5 and 6. Check for shorts/opens, replace U251. Check D251 and associated components. 2. Synthesizer fault Verify TRB line (from U201-2 to U251-19) is low in RX modeCheck for shorts, check U201 voltages per Ta b l e 6 - 4, replace U201 if incorrect. 3. Programming faultVerify RX channel programming is correct.Re-program if necessary. Synthesizer Out of Lock (TX mode only)1. VCO fault Verify oscillator is working, check RF level at U251-10 per schematic. Check dc voltages at U251 pins 1,3,4,10,15,16 per Ta b l e 6 - 4. Verify steering line voltage is between ~3 V and 10 V.Check VCO tank components connected to U251-15 and 16. Check for shorts/opens, replace U251. Check D261 and associated components. 2. Synthesizer faultVerify TRB line (U201-2 to U251-19) is high (3 V) in TX modeCheck for shorts, check U201 voltages per Ta b l e 6 - 4, replace U201 if incorrect. 3. Programming fault Verify TX channel programming is correct.Re-program if necessary. Synthesizer Out of Lock (RX and TX modes) 1. VCO faultCheck that RF level at U251-12 is at least 150 mV (VHF) or -12 to -20 dBm (UHF)If low/missing, check L276, C276-7, R276. 2. Synthesizer fault Check that RF level at U201-32 is at least 150 mV (VHF) or -12 to -20 dBm (UHF). Verify steering line voltage is between ~3 V and 10 V.If correct, check/replace U201. If incorrect, check R248 and C241. Check loop filter components R243-5 and C243-5. 3. DC voltage faultVerify 4.5 V dc at U201-28. Verify 12.1 V dc at U201-47Check C231-233, etc., for shorts. If OK check/replace U201. Check for 3 V 1.05 MHz sq waves at U201-14 and 15. Check C218-228, D220-221. 4. Programming fault Verify channel programming is cor- rect.Re-program if necessary.
June, 20056881096C25-B 6-4VHF Troubleshooting Tables: Troubleshooting Table for Transmitter 6.3 Troubleshooting Table for Transmitter Table 6-3. Troubleshooting Table for Transmitter Symptom Possible Causes Procedure Corrective Action No Transmit (no TX LED indication)1. PTT switch defective.Verify U401-71 goes low when PTT is pressed.Replace PTT switch S441. 2. EXT MIC PTT fault Verify U401-72 goes low when J471- 4 is grounded.Check/replace Q470, L471 etc. No Transmit (TX LED indication OK) 1. Synthesizer out of lockRefer to Table 6-2.Refer to Table 6-2. 2. No TX_ENABLE Verify U401-50 is high when pin 71 or 72 is low.Check/replace U401. 3. TX DC switch faultVerify Q171-C is 0 V in TX. Verify Q170-C is at Vbatt in TX.Replace Q171. Check for shorts, replace Q170. 4. Power control fault Check Q150 and U150 dc voltages per schematic and Table 6-4.Repair/replace defective com- ponents 5. No TX injectionCheck that RF level at jct. R100/ R101 per schematic.Check U251, L291-292, C290- 291. 6. No 5T source Verify Q312 gate is 0 V dc in TX Verify Q312 drain is 5 V dc in TX.Check/replace Q313. Check for shorts, check/replace Q312. 7. TX gain stage failureCheck RF levels at Q100 and U110 per schematic.Troubleshoot Q100/U110 and associated circuitry. 8. Antenna switch failure Verify dc voltage at jct. R122/L120 is approx 1.5 V.Check/replace D120-121, L120- 121, R120-122, etc.
6881096C25-BJune, 2005 VHF Troubleshooting Tables: Troubleshooting Table for Transmitter 6-5 Low Power 1. Low TX injectionCheck that RF level at jct. R100/ R101 per schematic.Check U251, L291-292, C290- 291. 2. Low gain in TX stage Verify dc voltage at Q100-E is ~1.3 V (VHF) or ~0.5 V (UHF). Verify that RF level at U110-1 is approx. 1 V (VHF) or 1.6 V (UHF).Verify 5T voltage is correct. Troubleshoot Q100 circuitry. Troubleshoot Q100 circuitry. Check/replace Q100. 3. Incorrect control volt- ageVerify that the dc voltage at PWR_SET (R162) is approx 1.8 V dc (at 1 watt) to 2.6 V dc (at 4-5 watts). Verify that the dc voltage at U110-2 is approx 2-3 V dc (at 1 watt) to 3-4 V dc (at 4-5 watts). (See schematic.)Check programming. Trouble- shoot controller circuitry. Check/ replace U451. Troubleshoot U150, Q150 and associated circuitry. 4. Antenna switch defect Verify dc voltage at jct. R122/L120 (VHF) or R121/L120 (UHF) is approx 1.7 V. Note: Do not attempt to mea- sure RF or DC voltages at the diodes. Damage to test equipment may occur.Check/replace D120-121, L120- 121, R120-122, etc. 5. Harmonic filter defectVisually inspect components C130- 137, L130-132. Check dc continuity of L130-132 in RX mode only.Repair/replace if necessary. Poor TX range, conducted power OK1. RF test jack defective Verify continuity of J140 pins 3 and 4 in RX mode only.Replace J140. 2. Antenna matching net- work faultVisually inspect components C140- 141, L140 or L141. Check dc conti- nuity of L140 or L141in RX mode only.Repair/replace if necessary. 3. Defective or wrong antennaVerify correct antenna is installed. Try another antenna.Replace antenna. No internal mic audio (EXT MIC audio OK) 1. Mic bias faultVerify U451-35 is low when side PTT is pressed. Verify Q470-6 is high when side PTT button is pressed.Check/replace U451. Check/replace R474, R476, and Q470. 2. Defective mic Verify approx 1.8 V dc across car- tridge when side PTT button is pressed. Verify audio present (~10 mV rms) when speaking into mic.Check mic connector and R478. Replace mic cartridge. 3. Defective mic jackVerify continuity between J471 pins 4 and 5.Replace J471. Table 6-3. Troubleshooting Table for Transmitter (Continued) Symptom Possible Causes Procedure Corrective Action
June, 20056881096C25-B 6-6VHF Troubleshooting Tables: Troubleshooting Table for Transmitter No EXT MIC audio 1. Mic bias fault Verify approx 1.8 V dc across EXT MIC cartridge in TX mode. Verify audio present (~10 mV rms) when speaking into mic.Check Q470. R475, R477, L471. Check VR473, VR475, D470 for shorts. 2. Audio path faultVerify mic audio present (~10 mV rms) at U451-46. Verify amplified mic audio present (~200 mV rms) at U451-40.Check L471, C470. Check/replace U451. 3. Defective audio acces- soryTry another accessory. Replace defective accessory. Table 6-3. Troubleshooting Table for Transmitter (Continued) Symptom Possible Causes Procedure Corrective Action