Motorola Portable Radio Ep450 Detailled Hkln4216c Manual
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HKLN4216CJune, 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...
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June, 2005HKLN4216C 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...
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HKLN4216CJune, 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...
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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...
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June, 2005HKLN4216C 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...
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HKLN4216CJune, 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...
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June, 2005HKLN4216C 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....
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HKLN4216CJune, 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...
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June, 2005HKLN4216C 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-...