Arcam-8R-int-sm维修电路原理图.pdf
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1、ALPHA ONE/7R/8R/8P AMPLIFIER SERVICE MANUALALPHA ONE/7R/8R/8P AMPLIFIER SERVICE MANUAL 1 Arcam Alpha One/ 7R/ 8R/ 8P Amplifier Service Manual Issue 1 Serial Number 001 - (Paul Newton/ Haider Bahrani Sept 98) Circuit Description The Alpha One / 7R/8R and 8P share a common pcb. The circuits are very s
2、imilar and the main differences are the remote volume facility and extra power output on the 7R and 8R and a switch to bypass the phono stage to enable its use as an extra line level input and the AV processor switch on the Alpha 8R integrated amplifier. The 8P power amplifier utilises the same powe
3、r amplifier circuit as the Alpha 8R integrated amplifier. Power Supplies The ac output of the toroidal mains transformer is rectified and smoothed by D201-204 and C204, 205. This is then regulated to +/-15V by Z201, 202 to power the phono and tone control stages and the d.c. servo. The Alpha 7R and
4、8R transformers have an extra tapping which is used for the remote volume circuit. The ac in is regulated to 5V by zener D902 and associated components and this is then used to power the microcontroller Z901 and remote receiver. Phono Stage (Not applicable to Alpha One) The phono stage consists of a
5、 dual opamp Z305, one opamp per channel. The RIAA equalization is achieved by the feedback components R703, 704, 702 and C704, 705, 702 on left channel (R603 etc. as above for Right channel). R703 determines the gain and C703 the low frequency roll off. On the Alpha 8R this stage can be bypassed by
6、use of switch SW302 to enable use as an extra line input. Tone Controls The tone control stage is based around Z304 a dual op amp. The range of the controls is set by R507, 508 for the bass pot RV302 and R509, 510 for the treble pot RV303. The tone controls and balance pot can be bypassed by use of
7、the direct switch, SW304. Power Amplifier The input to the power amplifier from previous stages is fed to the differential input of Q112 and Q113. Q110 and Q111 form a constant current source for the differential input stage. The output devices are n channel mosfets SMF045. Zener diodes D103,104 lim
8、it the voltage swing within safe limits for the output devices & fusible resistors R105, 106 provide overcurrent damage to the devices. A proportion of the output current appears across the protection network R41,42. If this becomes too high Q17 is turned on and mutes the output. High D.C. levels at
9、 the output will also mute the output. There are no output fuses on the Alpha One, 7R and 8R/8P amplifiers. The muting is done by the mute ic Z303 and its associated compontents. The mute operates on switch on/off and if an over current or over voltage condition occurs. The power led glows amber whe
10、n the mute circuit is operative and glows green in normal use. Removing the Alpha One/ 7R/ 8R/ 8P Transformer The toroidal transformer is extremely well secured to the main pcb with a double sided adhesive gasket. To remove the transformer you must break this adhesive bond by cutting through the gas
11、ket. This will be easier if the transformer is warm. Use a cheese wire under the transformer, pulling backwards and forwards under tension to gradually cut through. Once most of the adhesive is cut, you should be able to pull the transformer away from the pcb. A less satisfactory substitute for chee
12、se wire is to use some 22 gauge tinned copper wire, stretched first to remove kinks, and two temporary handles. Alpha One/7R/ 8R/ 8P Quiescent Current (IQ) Settings When replacing the output transistors of the above amplifiers it is important to reset the quiescent current (IQ) to the correct value
13、to prevent the amplifier blowing again. The IQ should be checked and set by following the procedure below: From cold and with no load or signal connected Turn both IQ presets (RV1 and RV101) down to minimum (fully anticlockwise) and set the voltage drop across resistor R1 (R101 for right hand channe
14、l) to between 3.0 and 3.5mV for the Alpha One and 7R RadioFans.CN 收音机爱 好者资料库 ALPHA ONE/7R/8R/8P AMPLIFIER SERVICE MANUALALPHA ONE/7R/8R/8P AMPLIFIER SERVICE MANUAL 2 amps or between 2.3 and 2.8mV for the Alpha 8R/8P amps. Leave the unit for 1 minute and reset to these values if required. Leave the u
15、nit for a further 5 minutes and reset if required. The IQ is now set and the unit can be connected to speakers and fully checked out. Disassembly For Servicing 1.Remove the top cover and front panel. 2.Remove 2 screws securing the sub front to the chassis sides and 3 screws holding the subfront to t
16、he chassis base. 3.Remove 1 screw holding the pcb to the chassis. This can be found near to the mains inlet socket. 4.Remove 5 screws from the rear panel, one at each end and 3 along the bottom edge. 5.Remove the transformer bolt. 6.Release the PCB pillar located near to the serial number on the pcb
17、. The pcb, with the rear panel, transformer and subfront attached, can now be pulled backwards out of the unit. TEST POINT VOLTAGES Test PointDC Voltage Alpha OneDC Voltage Alpha 7RDC Voltage Alpha 8R/8P 132.8V35V37V 227.8V29V31V 315V15V15V 4-32.8V-35V-37V 527.8V-29V-31V 6-15V-15V-15V 7N/A0.09V0.09V
18、 8N/A0.10V0.10V 90.3V0.27V0.27V 103.4V3.2V2.9V 1132.8V35V37V 12-3V-2.7V-2.5V 1332.8V-35V-37V Between 14 & 153.0 -3.5mV3.0-3.5mV2.3-2.8mV 16 (protection off)0.0V0.0V 16 (protection on)0.6V0.6V 170.0V0.0V 180.0V0.0V 190.0V0.0V RadioFans.CN 收音机爱 好者资料库 ALPHA ONE/7R/8R/8P AMPLIFIER SERVICE MANUALALPHA ON
19、E/7R/8R/8P AMPLIFIER SERVICE MANUAL 3 Test PointDC Voltage Alpha OneDC Voltage Alpha 7RDC Voltage Alpha 8R/8P 200.0V0.0V0.0V 21 (protection off)1.6V1.6V1.6V 21 (protection on)5.0V5.0V5.0V 220.58V0.17V0.17V 233.4V3.1V3.1V 24-3V-2.7V-2.7V 25-26V-29V-29V Between 26 & 273.4mV3.4mV2.5mV 28 (muted)35V35V3
20、5V 28 (protection off)1V1V1V 29N/A5V5V 30N/A10.510.5V 31 (volume going up) N/A0V0V 31 (volume going down) N/A5V5V 32 (volume going up) N/A0V0V 32 (volume going down) N/A5V5V PARTS LISTS The parts for all the units are as the Alpha 7 except where shown. REFDescriptionPart NoProduct C1ELST 100U 100V2N
21、710B7R C2PEST 47N 63V 10%2K3477R C3PCRB 100N 100V 5% RA 5mm 2H4107R C4PEST 47N 63V 10%2K3477R C5PSTY 33P 160V ENCAP 1PF% 2F0337R C7PPRO 4N7 63V 5% RA2D247N7R C8PPRO 100P 63V 5% RA2D110N7R C9ELST 100U 25V2N710A1 C10ELST 22U 20V OSCON2P6227R C10ELST 22U 63V ELECT2N622A1 C11ELST 100U 100V2N710B7R C12EL
22、ST 100U 100V2N710B7R C13PEST 15N 63V 10%2K3157R C14PEST 15N 63V 10%2K3157R C15SUPPR CAP 4N7 250V2K2477R C16ELST 100U 25V2N7107R C17CERD 470P 63V 20% RA2A1477R C18CERD 1N0 63V 20% RA2A2107R C19ELST 100U 25V2N7107R C20CERD 470P 63V 20% RA2A1477R C21CERD 10N 63V 20% RA2A3107R C22CERD 10N 63V 20% RA2A31
23、07R C23SUPPR CAP 4N7 250V2K2477R C24PPRO 4N7 63V 5% RA2D247N7R C25PCRB 100N 100V 5% RA 5mm 2H4107R C26PCRB 100N 100V 5% RA 5mm 2H4107R C27ELST 220U 16V2N7227R C28PCRB 100N 100V 5% RA 5mm 2H4107R ALPHA ONE/7R/8R/8P AMPLIFIER SERVICE MANUALALPHA ONE/7R/8R/8P AMPLIFIER SERVICE MANUAL 4 C29ELST 1U0 50V
24、20% RA2N5108R C30ELST 22U 63V ELECT2N6227R C30ELLL 47U 10V ELECT2R647A1 C30ELEC 10U 25V CERAFINE2P610CC8R C101ELST 100U 100V2N710B7R C102PEST 47N 63V 10%2K3477R C103PCRB 100N 100V 5% RA 5mm 2H4107R C104PEST 47N 63V 10%2K3477R C105PSTY 33P 160V ENCAP 1PF% 2F0337R C107PPRO 4N7 63V 5% RA2D247N7R C108PP
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