Arcam-Alpha7new-tun-sm 电路图 维修手册.pdf

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1、ALPHA 7 & 8 TUNER SERVICE MANUALALPHA 7 & 8 TUNER SERVICE MANUAL Issue 1 May 99 Page 1 of 14 Arcam Alpha 7/8 FM/AM Tuner Service Manual Issue 1 Serial Numbers beginning T7U . and T8U. (Paul Newton / Andy Howe / Simon Blandford May 99) Circuit Description The Alpha 7 and 8 tuners share the same print

2、ed circuit board and technical specification but the main functions of the Alpha 8 tuner can also be operated by remote control. Power Supply Mains voltage selection is made by placing a fuse, of appropriate value, in the 115V or 230V position. The single secondary is rectified and regulated and sup

3、plies four regulators. Z7 is always powered when the mains is connected and keeps the preset memory of the micro controller intact. The high-value capacitor (C84) will keep this data safe, for a limited time, in case of mains power failure. Z5 provides the main 12V supply rail for the RF and audio c

4、ircuits. This is always connected, except for the supply to the FM front end, which is disabled by Q2 when the unit is turned off. Z4 powers the LED back light on the display PCB. Z6 is the 5V digital supply for the micro controller. FM Tuner & IF The FM aerial input is mixed in the front end FE1 wh

5、ich provides a 10.7MHz IF output. This is filtered and amplified by ceramic filters CF1 & CF2 and the circuit based around Q9 & Q10. A third filter CF3 can be put in circuit by fitting jumpers JP1 & JP2 across pins 2 & 4 and 1 & 3 of SK6 respectively. This effectively narrows the IF band to improve

6、selectivity. Transistors Q17 and Q21 are part of the AGC circuit. The position of the jumper link JP7 to either SK10 or SK11 determines from which point the AGC circuit is triggered. The default is for the jumper to be fitted to SK10 which minimizes cross modulation and prevents the IF amp becoming

7、saturated. The LA1266 (Z9) demodulates the IF at pin 1 into an audio output at pin 12. The quadrature coil is a double-tuned device for best distortion performance. When a station is tuned correctly the On Tune signal goes low and drives a green LED on the display PCB. This signal is also used by th

8、e auto-stop detection and muting circuits. AM Tuner & IF The LA1266 (Z9) contains the AM RF amplifier, oscillator and mixer circuitry. Switching between FM and AM modes is controlled by the FM signal from the micro controller which disables the AM circuitry of Z9 and switches the path of the audio s

9、ignal through Z8. MW/LW switching is performed by switching transistors Q12, Q14 & Q15. Each band has its own oscillator and aerial tuning coils, tuned by a varicap diode all contained within the AM module L5. The 450kHz IF signal is filtered by coil and ceramic filter combination T5. Birdie Filter

10、The Birdie Filter (L2) is a four pole low pass filter, flat to about 53kHz, then with a very steep roll off from then on. This is designed to reduce co-channel interference in FM Stereo and cut down on irritating birdie noises. Stereo Decoder Stereo decoding is performed by LA3401 (Z8). The 38kHz re

11、ference signal is accurately created by ceramic resonator X3 and does not require adjustment. Stereo separation is adjusted for maximum by preset RV1. This IC also contains FM/AM audio switching and muting functions. Audio Filters & Output The left and right channel audio outputs from Z8 are filtere

12、d by the de-emphasis network of R1, C1 etc. The correct de-emphasis network is selected by the position of jumpers JP3 & JP4 on the pins of SK8. C2 & C102 (220pF) are selected for 50us and C3 & C103 (560pF) for 75us de-emphasis. The final filter, based on Z3, is a two-pole low-pass circuit with a cu

13、t-off frequency of around 20kHz. Also included is a 19kHz notch filter, L1 & C4, that removes most of the residual pilot tone. Muting When the power switch is turned off Q5 is switched off, enabling the mute circuitry of the stereo decoder (Z8) via diode D9. This removes the need for output muting t

14、ransistors and eliminates switching clicks and pops. At switch-on the mute is enabled while C21 is charged via Z8. In normal use the mute inside Z8 is enabled in three other ways: RadioFans.CN 收音机爱 好者资料库 ALPHA 7 & 8 TUNER SERVICE MANUALALPHA 7 & 8 TUNER SERVICE MANUAL Issue 1 May 99 Page 2 of 14 The

15、 AMUTE signal from the micro controller is active at power-on and for a short time when a preset is changed. When the band is changed the output is muted by charging C52. The audio output must be muted whenever the tuner is in stereo mode and is also off-tune. This is to eliminate noise during tunin

16、g and is provided by Q8 and the MONO and OFF TUNE control signals. In Mono mode this mute is disabled so that weak stations can be heard, despite the noise. Micro controller Control of the Alpha 7/8 tuners is performed by a single micro controller Z10, LA7230. This also provides keypad input and dri

17、ves a LCD directly. At power-on a matrix of diodes is scanned to set-up the controller for the correct options: D7 selects the correct frequency ranges. D10 enables the use of Auto tuning as well as manual tuning. D8 allows the Auto-tuning mode to use the IF Count method of searching. The position o

18、f jumpers JP 5 & JP6 fitted to SK9 are used to disable or enable LW and also whether the AM band steps are 9 kHz (UK) or 10 kHz (USA). Z10 provides control signal outputs for the following functions: MONOTo defeat the stereo decoder AMUTETurns on the mute circuit when a button is pressed & during tu

19、ning. FM, MW & LW Only one output active low at any one time. Used to switch on specific parts of the RF circuitry as appropriate. The micro controller includes a Phase-Locked-Loop (PLL) circuit which compares the tuner local oscillator signals (FMIN & AMIN) with a reference frequency. Based on this

20、 information and the required tuned frequency the controller varies the tuning voltage to the FM and AM front ends. The tuning voltages (FMVt & AMVt) have to be filtered from the PLL by the circuitry around Q7 & Q13. Display PCB The display PCB holds the keypad, LCD display, LED back light module an

21、d On-Tune indicator. A remote control receiver pcb is fitted on the Alpha 8 tuner only. This consists of the receiver RX1 and the PIC micro controller, Z1, which is used to decode the incoming remote control codes from RC5 format to Sanyo type commands. This is because the Sanyo micro controller, Z1

22、0, can only respond to Sanyo remote control commands. Disassembly For Servicing To remove the board within the tuner follow the instructions below. 1.Remove the top cover. 2.Remove the 4 screws holding the front panel to the chassis and release the locating tabs. 3.Unplug the 2 display board flexfoi

23、ls where they enter the main pcb. 4.Remove the 2 screws holding the remote receiver pcb in place if it is an Alpha 8 tuner. 5.The front panel can now be pulled off the unit. 6.To remove the display pcb remove the 10 screws holding the board in place. To remove the main pcb remove the 7 pcb securing

24、screws and the screw holding the audio output and aerial sockets to the chassis. The main pcb can now be slid out of the case. RadioFans.CN 收音机爱 好者资料库 ALPHA 7 & 8 TUNER SERVICE MANUALALPHA 7 & 8 TUNER SERVICE MANUAL Issue 1 May 99 Page 3 of 14 Test Method Bench Test and Set-up Procedure Equipment:RF

25、 signal generator, covering AM & FM frequency bands Multiplex stereo signal generator Distortion analyser Digital Volt Meter Oscilloscope Setting up: Generator settings unless otherwise stated: FM RF Output level1mV emf = 60dBuV RF frequency98MHz Modulation frequency1kHz Modulation level75kHz AM RF

26、Output level1mV emf = 60 dBuV RF frequency1MHz (MW). 200kHz (LW) Modulation frequency1kHz Modulation level30% The AM generator should be connected to the antenna connections though a 10K resistor. A 12uH inductor should be connected across the antenna connections. This simulates the loop ariel we su

27、pply to the customer. 10K may seems quite a high resistance however this is to stop the generator de-tuning the antenna coils. Tuner settings: The Alpha 7/8 tuners presets are pre-programmed to frequencies that are useful during the test procedure- FM preset398MHz AM preset1522kHz 2603kHz 3999kHz 41

28、404kHz 51611kHz 6146kHz 7270kHz 8290kHz 1.Power Supplies Test no.DescriptionTP/Adjustment point LimitsUnit MinMax 1Unregulated SupplyTP11622V 2Audio & RF SupplyTP211.512.5V 3Backlight SupplyTP311.512.5V 4Digital SupplyTP44.55.5V 5Back-up SupplyTP55.35.7V RadioFans.CN 收音机爱 好者资料库 ALPHA 7 & 8 TUNER SER

29、VICE MANUALALPHA 7 & 8 TUNER SERVICE MANUAL Issue 1 May 99 Page 4 of 14 2.FM Distortion, Filters & Separation Test no.DescriptionTP/Adj point LimitsUnit MinMax 6Adjust the Quadrature coil, L4 with the tuner locked to the following signal. Frequency = 98.0MHz Deviation = 22.5KHz (30%), Mono RF Level=

30、 60dBuV ENSURE THAT THE AUTO-SEARCH SYSTEM WORKS IN BOTH DIRECTIONS, TUNING TO THIS SIGNAL. TP93.94.1V 7Adjust the other half of the Quadrature coil, L3 for minimum distortion in MONO mode. Deviation = 22.5kHz (30%) RF Level= 60dBuV A-0.1% 8IHF sensitivity , 100% dev., MONO mode RF Level= 60dBuV -20

31、dBu 9Stereo, pilot tone only Check Stereo LED Adjust L1 (left) & L101 (right) for minimum output D E - 10Stereo, 1kHz 30% dev. RF Level= 60dBuV Measure distortion LEFT RIGHT - - 1.5 1.5 % % 11Stereo L on, R off. Stereo, 1kHz 30% dev. RF Level= 60dBuV Adjust RV1 for minimum right output Measure cross

32、talk LR -38dB 12Stereo L off, R on. Stereo, 1kHz 30% dev. RF Level= 60dBuV Check crosstalk RL and adjust RV1 for equal with LR -38dB 3. Frequency response Test no.DescriptionTP/Adj point LimitsUnit MinMax 13Stereo 1kHz mod 30% dev. RF Level= 60dBuV Measure L output -15-13dBV 14RF Level= 60dBuV Stere

33、o 1kHz mod 30% dev. Check channel balance -1.0dBr ALPHA 7 & 8 TUNER SERVICE MANUALALPHA 7 & 8 TUNER SERVICE MANUAL Issue 1 May 99 Page 5 of 14 15RF Level= 60dBuV Stereo 1kHz mod 30% dev. Set modulation frequency to 10kHz and re-measure channel balance -1.0dBr 16RF Level= 60dBuV Stereo 1kHz mod 30% d

34、ev. Set reference audio ouput level to 0dBr 1kHz on Left channel 1720Hz modulation LEFT RIGHT -0.2+0.0dBr dBr 186.3kHz modulation LEFT RIGHT 0.0+0.5dBr dBr 1910kHz modulation LEFT RIGHT 0.0+0.6dBr dBr 2015kHz modulation LEFT RIGHT 0.0+3.0dBr dBr 21Switch off modulation Measure Stereo CCIR noise -72d

35、BV 22Mod off Select MONO. Check that Stereo LED goes out. Measure Mono CCIR noise -77dBV 4AM (MW) Alignment Test no.DescriptionTP/Adj point LimitsUnit MinMax 23Tune to 522kHz (preset 1) Check the tuning voltage. TP81.01.5V 24Tune to 1611kHz (preset 5) Check that the tuning voltage is TP86.57.5V 5LW

36、Alignment Test no.DescriptionTP/Adj point LimitsUnit MinMax 25Tune to 146kHz (preset 6) Check that the tuning voltage is TP81.52.0V 26Tune to 290kHz (preset 8) Check that the tuning voltage is TP86.07.0V ALPHA 7 & 8 TUNER SERVICE MANUALALPHA 7 & 8 TUNER SERVICE MANUAL Issue 1 May 99 Page 6 of 14 6AM

37、 Audio Tests Test no.DescriptionTP/Adj point LimitsUnit MinMax 27Tune to 999kHz (preset 3) Modulation 1kHz 30%. RF Level= 60dBuV Record audio O/P level dBV 28100Hz modulation. Record audio O/P level-1.0+0.0dBr 1kHz 293kHz modulation. Record audio O/P level-6.0+0.0dBr 1kHz 30Modulation off. Measure C

38、CIR noise-60dBV 31Modulation 1kHz 30%. Measure THD-0.5% 32Measure RF level for -40dBV noise-40dBuV Test Points (marked on Circuit Diagrams and PCB) Test Points TP1Unregulated power supply TP2Audio & RF supply TP3Backlight supply TP4Digital supply TP5Back-up supply TP6Signal strength level TP7AM loca

39、l oscillator TP8Tuning voltage TP9FM center voltage Adjustment Points AFM Quadrature Coil - first stage BFM Quadrature Coil - second stage CStereo Separation Preset DLeft channel 19kHz notch filter ERight channel 19kHz notch filter FAM IF transformer ALPHA 7 & 8 TUNER SERVICE MANUALALPHA 7 & 8 TUNER

40、 SERVICE MANUAL Issue 1 May 99 Page 7 of 14 Test Pads (marked on Circuit Diagrams only)(all prefixed with A_) Power Supply LIVEMains live NEUTMains neutral 230VLive after 230V fuse 115VLive after 115V fuse SECATx secondary, 17Vac in standby, 16Vac in use +/-2Vac SECBTx secondary SWAUnregulated suppl

41、y - before power switch 20.8Vdc standby, 18.2Vdc in use +/-2.5Vdc SWBAfter power switch 18.2Vdc in use +/-2.5Vdc GNDPower ground P12V12V supply +/-1V VBLBacklight supply 12Vdc +/-1V P5V5V supply to micro +/-0.5V P5V65.6V backup supply +/-0.7V RF FMRFFM aerial input, 75Ohm source impedance AMRFAM aer

42、ial input, 50Ohm in series with 220uH source impedance FMGNDAerial ground (FM) AMGNDAerial ground (AM) FMLOFM local oscillator output 1) 125mVac +/- 20mV, 118.7MHz with 108MHz selected on display. 2) 155mV +/-20mV, 98.2MHz with 87.5MHz selected on display. Measured with spectrum analyzer with high i

43、mpedance probe. AMLOAM local oscillator output 200mVac +/- 50mV 596KHz to 2.061MHz over LW and MW tuning range 146KHz to 1.611Mhz. Measured with spectrum analyzer with high impedance probe. FMVTFM tuning voltage, between 0.5V and 10V at frequency extremes of FM. AMVTAM tuning voltage, between 0.5V a

44、nd 10V at frequency extremes of MW and LW. ONTUNEOn-tune indicator output 5V=not on tune, 0V=on tune SMETERSignal strength meter output. 20uV carrier at 98MHz should yield 1.6V +/-0.5V. IFOUTIF output from front end.1mV carrier input at 98MHz should yield 5mV +/-3mV. Measured with spectrum analyzer

45、with high impedance probe. FMINFM IF input to demodulator. 1mV carrier input at 98MHz should yield 30mV +/- 10mV here at 10.7MHz. 1mV 10.7MHz (I.F. breakthrough) input should yield 30uV. 1mV 119.4MHz (image breakthrough) should yield 30uV. Measured with spectrum analyzer with high impedance probe (1

46、0KHz BW). ALPHA 7 & 8 TUNER SERVICE MANUALALPHA 7 & 8 TUNER SERVICE MANUAL Issue 1 May 99 Page 8 of 14 AMSIG1AM I/P from coils. This test is only possible using a spectrum analyzer with high impedance probe and 10KHz bandwidth. MW Test: Applying 50mV 999KHz through the 10K resistor and with 12uH acr

47、oss the input should yield 3.2V +/- 1V at 999KHz. Tune L5, black trimmer coil to peak signal. Applying the same signal at 450KHz (IF freq) should yield 110uV +/- 50uV. Applying the same signal at 1899KHz (image freq) should yield 16uV +/- 10uV. LW Test: Applying 50mV 198KHz through the 10K resistor

48、and with 12uH across the input should yield 1.3mV +/- 1V at 198KHz. Tune L5, sunken red trimmer coil to peak. Applying the same signal at 450KHz (IF freq) should yield 25uV +/- 10uV. Applying the same signal at 1098KHz (image freq) should yield 60uV +/- 30uV. AMSIG2AM IF to IF filter. No useful test

49、s can be carried out at this point. AMSIG3AM IF from IF filter. This test is only possible using a spectrum analyzer with high impedance probe and 10KHz bandwidth. MW Test: Applying 1mV 999KHz through the 10K resistor and with 12uH across the input should yield 1.3V +/- 500mV at 450KHz. Tune L5, black trimmer coil to peak signal. Applying the same signal at 450KHz (IF freq) should yield 25uV +/- 20uV. Applying the same signal at 1899KHz (image freq) should yield