Cambridge Audio 740A Service Manual
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Cambridge Audio 740A Service Manual

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See also: Code List , User Manual
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Issue Date: 8
August 2007

SERVICE MANUAL

SPECIFICATIONS:

Power Output
THD (unweighted)
Frequency Response
S/N Ratio (ref 1W/8 Ohms)
Input Impedances
Power Amp Damping Factor
Max Power Consumption
Minimum Power Consumption
Bass & Treble Controls
Dimensions
Weight
Gallery Court Hankey Place London SE1 4BB UK
Tel: +44 (0)20 7940 2200 Fax: +44 (0)20 7940 2233
100W RMS into 8 Ohms
150W RMS into 4 Ohms
< 0.001% 1 kHz
At 80% of rated power
< 0.01% 20 Hz – 20 kHz
At 80% of rated power
10 Hz – 50 kHz +/- 1 dB
> 96 dB
Inputs 1-6 47 kOhm
> 110 at 1 kHz
750W
Active (no signal) 45W
Standby 6W
Shelving Type
Max bass boost/cut
+/-10 dB at 10 Hz
Max treble boost/cut
+/- 7.5 dB at 20 kHz
115 x 430 x 350mm
(4.5 x 16.9 x 13.8")
10.7kg (23.5Lbs)
740A
AP22267/1
1

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Summary of Contents for Cambridge Audio 740A

  • Page 1: Service Manual

    740A Issue Date: 8 August 2007 SERVICE MANUAL SPECIFICATIONS: Power Output 100W RMS into 8 Ohms 150W RMS into 4 Ohms THD (unweighted) < 0.001% 1 kHz At 80% of rated power < 0.01% 20 Hz – 20 kHz At 80% of rated power Frequency Response 10 Hz –...
  • Page 2 740A SERVICE MANUAL TABLE OF CONTENTS Safety Precautions & Important Notes Exploded Diagrams Exploded Diagram Parts List Front Panel PCB Schematic (Tone Control) Front Panel PCB Schematic (Microcontroller & LCD) Front Panel PCB Layout (Top Side) Front Panel PCB Layout (Bottom Side)
  • Page 3 IC Pin Layout Details____________________________________________ 46‐51  Service Mode Instructions________________________________________52  Procedure to Upgrade Software___________________________________ 53  Kanda PIC Hand Held Programmer Modification Instructions____________54‐58  Revised Front Panel Schematic–to improve encoder reliability:   (see Service Bulletin TNBC‐0035)__________________________________ 59‐60   ...
  • Page 4 COPYRIGHT NOTICE. © 2007 Audio Partnership PLC. All rights reserved. Cambridge Audio and Azur are registered trademarks for Audio Partnership PLC. This document may not be reproduced, distributed, transmitted, displayed, published, or broadcast without the express written prior permission of Audio Partnership PLC.
  • Page 14 AP19787/4 Cambridge Azur 740A Front Panel PCB Assembly BOM AP Part Value Description/Type Component Ident Type Tolerance Factory P/N Notes RESISTORS 1/4W Metal Film R8, R9 1/4W Metal Film 1/4W Metal Film R1, R2 100R 1/4W Metal Film 220R 1/4W Metal Film...
  • Page 15 AP19787/4 Cambridge Azur 740A Front Panel PCB Assembly BOM AP Part Value Description/Type Component Ident Type Tolerance Factory P/N Notes INTEGRATED CIRCUITS Program with software: PIC16F877A- 40 Pin Flash Microcontroller AP20357/x Please add version label! M74HC4094 PY524 M74HC4094B 8 Bit Shift Register...
  • Page 23 AP19802/5 Cambridge Audio Azur 740A Preamp PCB Assembly BOM AP Part Value Description/Type Component Ident Type Tolerance Factory P/N Notes RESISTORS 1/4W Metal Film R1, R3, R6, R8 4.7R 1/8W Metal Film 2W Carbon R17, R18 1/4W Metal Film R37, R38...
  • Page 24 AP19802/5 Cambridge Audio Azur 740A Preamp PCB Assembly BOM AP Part Value Description/Type Component Ident Type Tolerance Factory P/N Notes 100k 1/8W Metal Film R69, R126 470k 1/4W Metal Film R56, R57 CAPACITORS No fit C27, C28, C30, C57 No Fit...
  • Page 25 AP19802/5 Cambridge Audio Azur 740A Preamp PCB Assembly BOM AP Part Value Description/Type Component Ident Type Tolerance Factory P/N Notes With Cambridge 1102-222034- 2200uF 35V Electrolytic C26, C32 Sleeving as per 640C V2 CONNECTORS 2300-006000- 6 Way Straight Header 2330-005901- Stereo 6.35mm...
  • Page 26 AP19802/5 Cambridge Audio Azur 740A Preamp PCB Assembly BOM AP Part Value Description/Type Component Ident Type Tolerance Factory P/N Notes 4139- Low Offset Dual Comparator U13, U14 LM393AP 300052E900 RELAY 4050-000005- PY504 5V 2A 2P2T Relay RL1, RL2 ME2-5S TRANSISTORS...
  • Page 34 Cambridge Azur 740A Amp PCB Assembly BOM AP19797/6 AP Part No. Value Description/Type Component Ident Type Tolerance Factory P/N Notes RESISTORS R27, R65, R78, R113, 0.22R 3W Wirewound 1072-208330E000 R132-R135 24AWG Wire Link R30, R68 4.7R 3W WireWound R28, R66...
  • Page 35 Cambridge Azur 740A Amp PCB Assembly BOM AP19797/6 AP Part No. Value Description/Type Component Ident Type Tolerance Factory P/N Notes C1, C2, C46, C47, 39nF 250V Metallised Polyester C52, C57, C58, C60 47nF 63V Polyester C9, C21, C29, C38 1117-473053-000...
  • Page 36 Cambridge Azur 740A Amp PCB Assembly BOM AP19797/6 AP Part No. Value Description/Type Component Ident Type Tolerance Factory P/N Notes Q12, Q13, Q17, Q18, Q31, Q36- PY537 300V 500mA NPN Signal MPSA42 1300-420000-100 Q38, Q40, Q41, Q43-Q45, Q49 PF075 -120V -100mA...
  • Page 40 AP19929/1 Cambridge Audio Azur 740A ABUS Hub PCB Assembly BOM AP Part No Value Description/Type Component Ident Type Tolerance Factory P/N NOTES RESISTORS 1/4W Metal Film R29, R34, R36, R44, 0805 Thick Film R46, R51 Stand off PCB 100R 1/4W Fusible...
  • Page 41 AP19929/1 Cambridge Audio Azur 740A ABUS Hub PCB Assembly BOM AP Part No Value Description/Type Component Ident Type Tolerance Factory P/N NOTES Headphone Jack 3.5mm 2320-003911E007 Green 3.5mm Jack CN7, CN8 2320-004911E002 Vertical 2 Way Horizontal Must Have 2330-004900E002 Phono...
  • Page 45 Cambridge Azur 740A Mains PCB Assembly BOM AP19792/5 AP Part No. Value Description/Type Component Ident Type Tolerance Factory P/N Notes RESISTORS 220R 2W Carbon 1/8W Metal Film R2, R24 1/8W Metal Film R1, R25 CAPACITORS 1nF 400V X1/Y1 Mains Rated...
  • Page 46 Cambridge Audio Azur 740A Amplifer IC Pin Layout Details BD140 Input PCB - (Q1 & Q4) Preamp PCB – (Q1 & Q5) BD139 Input PCB - (Q2, Q3, Q5 & Q6) Preamp PCB – (Q2, Q3, Q4 & Q6) BC327-25 Input PCB - (Q7) Preamp PCB –...
  • Page 47 L7805 Input PCB - (U3) L7815CV Input PCB - (U4) LM393A Input PCB - (U8) TC9163AF Input PCB - (U11) Preamp PCB – (U10) PIC16F877A-I/P Front Panel PCB - (U1) M74HC4094B Front Panel PCB - (U2)
  • Page 48 TSOP34836 Front Panel PCB - (U3) M74HC02 Front Panel PCB - (U4) NE5532P Front Panel PCB - (U100 & U200) Preamp PCB – (U1, U9, U11, U12, U15, U16, U17, U18, U19 & U20) 2SC2240GR Amp PCB - (Q1, Q6, Q7, Q15, Q23, Q24, Q26 &...
  • Page 49 MPSA92 Amp PCB - (Q3, Q4, Q8, Q25, Q28, Q29, Q30, Q33, Q39, Q42, Q46, Q47 & Q48) MPSA42 Amp PCB - (Q9, Q10, Q12, Q13, Q17, Q18, Q19, Q20, Q31, Q36, Q37, Q38, Q40, Q41, Q43, Q44, Q45 & Q49) SAP15PY Amp PCB - (Q51, Q53, Q56 &...
  • Page 50 L7915 Preamp PCB - (U4) L7805 Preamp PCB - (U5) LM337T Preamp PCB - (U6 & U7) LM317T Preamp PCB - (U8) LM393AP Preamp PCB - (U13 & U14) HEF4011BT Abus Hub PCB - (U1) OP4N25 Abus Hub PCB - (U2) TSOP34837 Abus Hub PCB - (U3)
  • Page 51 NJM5532M Abus Hub PCB - (U4 & U5) L7812 Abus Hub PCB - (U6) TSOP34836 Abus Hub PCB - (U7) BC846 Abus Hub PCB - (Q1, Q3 & Q4) BC856B Abus Hub PCB - (Q2)
  • Page 52 Cambridge Azur 740A Amplifier Service Mode Instructions Press and hold the mode button while turning the rear panel mains power on. Please note: The ‘counters’ menu is particularly useful to examine the history of use/misuse of the amplifier. The LCD display will show SERVICE with these menu options:...
  • Page 53 Once the appropriate hex file is loaded to the programmer, pressing the red download button should be followed shortly by a green light on the programmer to indicate successful download. To confirm the software revision number contained in the 740A, access the service mode. Connector on rear of front panel:...
  • Page 54 Kanda PIC Hand Held Programmer Modification Instructions To Programme Cambridge Audio Products: Programmer Used Sourced From: http://www.kanda.com There are two product codes which will get you the same programmer that is used at AP: 1. PIC HH0010. This comes with the PC PIC Upload Software on CD.
  • Page 55 4. Cut the orange wire, then strip and tin 5mm off each other wire (see picture below). 5. Take the Flat 06 Way 250mm cable assembly and cut off one of the plugs. Strip and tin 5mm off each wire (see picture below). 6.
  • Page 56 Brown wire to wire 5 7. Wrap insulation tape around each solder joint (see picture below). 8. Heatshrink the assembly joints for added protection and to finish. 9. Load up the “PICkeyfob Programmer” software on your PC. 10. Save the supplied PIC HEX file to a suitable location on your PC. 11.
  • Page 57 15. Connect the “yellow programmer” to the PC’s parallel port using the 10 pin IDC to parallel converter and 10 pin IDC to 10 pin IDC cable. 16. Press the “Upload” button in the “PICkeyfob Programmer” window to start the upload process into the PIC programmer.
  • Page 58 20. Disconnect the programmer (with the 10 pin IDC to 10 pin IDC cable) from the 10 pin IDC to parallel converter. 21. Connect the modified cable assembly to the 10 pin IDC to 10 pin IDC cable socket. 22. Programme the Cambridge Audio unit according to the separate instructions supplied, where appropriate. The process is now complete.
  • Page 59 6 Way Right Angle Header 4 Way CN10 Straight Header -15V C104 See AP20043/1 47nF 63V 6 Way to 4 Way Met. Polyester Screened Audio cable C103 U100:B C101 NE5532P 1.5nF 63V Audio Op Amp RIGHT LK38 Met. Polyester 10pF 50V NP0 Ceramic 1/8W Metal Film 24 AWG...
  • Page 60 TO POWER AMP PCB COL 1 COL 2 COL 3 CN11 RC5 BLOCK SPEAKER B RELAY LK11 RC5 TX SPEAKER A RELAY PHONES DETECT PREAMP RELAY LK14 24 AWG LK32 KPT-1105A KPT-1105A KPT-1105A DIRECT RELAY 24 AWG VI/SHORT INPUT 1 INPUT 2 INPUT 3 24 AWG...

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