TM-271A Service manual - The Repeater Builder's Technical ...

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TM-271A/271E CIRCUIT DESCRIPTION ■ Unlock Circuit During reception, the 8RC signal goes high, the 8TC signal goes low, and Q34 turns on. Q33 turns on and a voltage is applied to 8R. During transmission, the 8RC signal goes low, the 8TC signal goes high and Q36 turns on. Q35 turns on and a voltage is applied to 8T. The CPU monitors the PLL (IC401) LD signal directly. When the PLL is unlocked during transmission, the PLL LD signal goes low. The CPU detects this signal and makes the 8TC signal low. When the 8TC signal goes low, no voltage is applied to 8T, and no signal is transmitted. (See Fig. 7.) 8R Q33 SW 8C Q35 SW 8T Transmitter System ■ Outline The transmitter circuit produces and amplifies the desired frequency directly. It FM-modulates the carrier signal by means of a varicap diode. ■ Power Amplifier Circuit The transmit output signal from the VCO passes through the transmission/reception selection diode (D409) and amplified by Q501, Q502 and Q503. The amplified signal goes to the final amplifier (Q504) through a low-pass filter. The lowpass filter removes unwanted high-frequency harmonic components, and the resulting signal is transmitted through the antenna terminal. (See Fig. 8.) 8RC Q34 SW Fig. 7 IC101 CPU Q36 SW LD 8TC IC401 PLL PLL lock : LD “H” Unlock circuit ■ APC Circuit The automatic transmission power control (APC) circuit detects part of a final amplifier output with a diode (D606, D607) and applies a voltage to IC501. IC501 compares the APC control voltage (PC) generated by the D/A converter (IC161) and DC amplifier (IC203) with the detection output voltage. IC501 generates the voltage to control Q503 and Q504 and stabilizes transmission output. The APC circuit is configured to protect over current of Q503 and Q504 due to fluctuations of the load at the antenna end and to stabilize transmission output at voltage and temperature variations. (See Fig. 9.) MIC IC201 MIC/IDC IC202 SPLATTER FILTER IC203 SUM AMP IC161 D/A CONVERTER IC203 BUFFER MIC KEY INPUT IC101 CPU IC161 D/A CONVERTER ANT IC161 D/A CONVERTER Q406 VCO Q410 BUFFER IC402 1/2 DIVIDER Q411 RF AMP Q501 RF AMP Q502 PRE DRIVE AMP Q503 DRIVE AMP Q504 FINAL AMP X401 Q404 TCXO 16.8MHz PLL RF AMP IC401 Fig. 8 Transmitter system D409 Q501 RF AMP Q502 PRE DRIVE AMP Q503 DRIVE AMP Q504 FINAL AMP D602,D603 D605 ANT SW LPF ANT IC161 (PC/TVO) IC203 DC AMP (PC) IC501 APC CONTROL VR601 D606 D607 POWER DET 4 Fig. 9 APC circuit
CIRCUIT DESCRIPTION TM-271A/271E Control Circuit The CPU carries out the following tasks (See Fig. 10.): 1) Controls the WIDE, NARROW, TX/RX outputs. 2) Adjusts the AF signal level of the AF filter (IC251) and turns the filter select compounder on or off. 3) Controls the display unit. 4) Controls the PLL (IC401). 5) Controls the D/A converter (IC161) and adjusts the volume, modulation and transmission power. IC101 CPU CK DT LD PLLE IC161 D/A converter IC401 PLL ■ Memory Circuit The transceiver has an 64k-bit EEPROM (IC66). The EEPROM contains adjustment data. The CPU (IC101) controls the EEPROM through three serial data lines. (See Fig. 11.) EEPCK IC101 CPU EEPSDT EEPWP IC66 EEPROM ■ Display Circuit The CPU (IC101) controls the display LCD and LEDs. When power is on, the LCD driver will use the BL line to control the LCD illumination and key backlight LEDs. The brightness function is controlled by the switch Q12. The LCD driver (IC3) and CPU (IC101) communicate through the CE, CL, DI, DO lines. (See Fig. 12.) IC101 CPU Fig. 10 Fig. 11 CE CL DI DO BL Control circuit Memory circuit IC3 LCD driver COM0~ COM3 SEG0~ SEG30 LCD ■ Key Matrix Circuit The TM-271 front panel has function keys. Each of them is connected to a cross point of a matrix of the KI1 to KI3 and KSI to KS2 ports of the LCD driver. The LCD driver monitors the status of the KI1 to KI3 and KS1 to KS2 ports. If the state of one of the ports changes, the LCD driver assumes that the key at the matrix point corresponding to that port has been pressed. IC3 LCD driver KI1 KI2 KI3 KS2 KS1 FUNC REV MHz (Encoder) CALL VFO MR ■ Encode The DCS and CTCSS signals are output from QT/DQT of the CPU (IC101) and summed with the external pin DI line by the summing amplifier (IC203) and the resulting signal goes to the D/A converter (IC161). The DTMF signal is output from DTMF pin of the CPU and summed with a MIC signal by the summing amplifier (IC203), and the resulting signal goes to the D/A converter (IC161). The D/A converter (IC161) adjusts the MOD level and the balance between the MOD and CTCSS/DCS levels. Part of a CTCSS/DCS signal is summed with MOD and the resulting signal goes to the VCOMOD pin of the VCO. This signal is applied to a varicap diode in the VCO for direct FM modulation. TONE IC101 CPU DTMF Fig. 13 QT/DQT (CPU1) DTMO (EVOL15) Key matrix circuit IC203 SUM AMP DI IC203 SUM AMP TCXO MOD X401 TCXO IC161 D/A VCO MOD IC401 PLL VCO Amp Q6 SW Q10 SW D2~D4 Fig. 14 Encoder Q9 SW D19~D30 Q12 SW BRI Fig. 12 Display circuit 5
Page 1 and 2: VHF FM TRANSCEIVER TM-271A/271E SER
Page 3: CIRCUIT DESCRIPTION TM-271A/271E
Page 7 and 8: CIRCUIT DESCRIPTION TM-271A/271E
Page 9 and 10: COMPONENTS DESCRIPTION TM-271A/271E
Page 11 and 12: Ref. No. Address New Parts No. Desc
Page 13 and 14: PARTS LIST TM-271A/271E Ref. No. Ad
Page 15 and 16: PARTS LIST TM-271A/271E Ref. No. Ad
Page 17 and 18: EXPLODED VIEW TM-271A/271E A B 1 A
Page 19 and 20: RESETTING THE TRANSCEIVER TM-271A/2
Page 21 and 22: ADJUSTMENT TM-271A/271E Adjustment
Page 23 and 24: ADJUSTMENT TM-271A/271E Adjustment
Page 25 and 26: ADJUSTMENT TM-271A/271E Item Condit
Page 27 and 28: TERMINAL FUNCTION TM-271A/271E TX-R
Page 29 and 30: J K L M N O P Q R S PC BOARD TM-271
Page 31 and 32: I 1 2 A B J1 EXT. SP C D TM-271A/27
Page 33 and 34: I 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Page 35 and 36: Q501 R426 R509 R507 C507 C511 TC401
Page 37 and 38: TM-271A/271E SCHEMATIC DIAGRAM 34 7
Page 39 and 40: TM-271A/271E SCHEMATIC DIAGRAM 36 K
Page 41 and 42: -t -t -t C422 470p C33 1000p C559 0
Page 43 and 44: TM-271A/271E 39 BLOCK DIAGRAM DT Q3
Page 45 and 46: LEVEL DIAGRAM TM-271A/271E 450kHz A

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