User manual SOUNDCRAFT CPS800 POWER SUPPLY

[. . . ] Soundcraft shall not be liable for any loss or damage whatsoever arising from the use of information or any error contained in this manual, or through any mis-operation or fault in hardware contained in the product. No part of this manual may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, electrical, mechanical, optical, chemical, including photocopying and recording, for any purpose without the express written permission of Soundcraft. It is recommended that all maintenance and service on the product should be carried out by Soundcraft or its authorised agents. Soundcraft cannot accept any liability whatsoever for any loss or damage caused by service, maintenance or repair by unauthorised personnel. Harman International Industries Ltd. [. . . ] The drop across these at full load is approx 200mV which is more than enough to swamp Vbe differences in the main transistors. 50 Amp Schottky diode D7 on the output allows supplies to be paralleled for redundancy. The Mains Voltage Meter. The incoming mains voltage is continuously indicated on the front panel by a 3. 5 Digit Panel Meter. (DPM) This is powered from a +5V supply derived from the +12V subrail by 7805 regulator REG2. The +5V supply is reduced to +2. 5V by R30, 31, and buffered by IC2-A to generate a half-rail for the DPM input. The incoming mains is monitored by differential amplifier IC1-A, which looks at the voltage between Live and Neutral; this avoids problems with having one side of the meter connected to Earth, which is often not at quite the same potential as Neutral. The Voltage is picked off via two special BSI safety-approved 680K resistors on the voltage select PCB (SC3817) which connect to CN3. The circuitry around IC1-A (R21-24) gives unity gain, but the presence of the 680K resistors on the input gives suitable scaling of the 50Hz signal. The signal is applied to precision full-wave rectifier IC1-B, IC2-B via DC-blocking cap C5; this circuit is biased by the +2. 5V halfrail. The rectified output is smoothed by C6 and scaled by R39 and PR1 before applying it to the DPM input on CN1 Pin 8. (IN HI) Note the DPM has a differential input, so the cold side (IN LO, Pin 7) is connected to the +2. 5V halfrail. The Mutual Shutdown System. Equipment containing some kinds of op-amp is vulnerable to damage when only one of the +/-17V rails fails, as in this case excessive supply currents can be drawn, damaging fuse resistors on the modules. When both 17V supplies are working normally, current flows through DZ8, OPTO1, and across to the RH PCB. This subrail is generated from the AC input to the PCB by charge-pump C41, 42, D22, 23. The resulting negative voltage is stabilised by 8V2 Zener DZ10, and applied to R73. This keeps the tail current of TR18, 19 more constant, and so maintains the transconductance (current out for voltage in) at a higher level, giving closer feedback control of current-limiting under extreme conditions. The RH PCB operates identically. 18 Circuit Description Undervoltage warning. The supply gives a warning indication when the mains voltage has fallen so low that regulation is about to be lost. The Headroom Indicator subsystem illuminates all the decimal points on the DPM, giving a clear signal that something is amiss. The voltage across the pass transistors is monitored by TR3; when this voltage falls too low, TR3 turns off, turning off TR1. TR1 collector is then pulled up to +40V by R26, charging C7 through D5, and so turning on TR2. This connects the DPM decimal point connections to the local 0V (actually +26 TO +29V above supply 0V) via current-limiting resistors R32-34. The peak-hold action of D5/C7 is required as the voltage across the pass transistors includes a large ripple content that would leave the decimal points rather dim if they were being strobed at 100 Hz. An identical circuit (TR9, TR10) monitors headroom in the -17V supply. TR9 collector is connected to the LH PCB via connectors CN8-CN7, and the cessation of current drawn indicates low headroom. [. . . ] RY8009 !5X20MM T2A/250V AS FUSE !5X20MM T10A/250V AS FUSE !5X20MM T12. 5A/250V AS FUSE !CPS800 POWER SUPPLY FUSE 32A BS88 CPS800 POWER SUPPLY USER&TECH GUIDE 26 Parts List MAIN ASSEMBLIES !CPS800 POWER SUPPLY STAR POINT PCB W/Form W/Form W/Form W/Form W/Form W/Form W/Form W/Form W/Form . TO3 INSULATING WASHER D7 (on SC3804-09) REG1 REG2 TR4 TR5 TR6 TR7 TR8 TR17 W/Form . RA4032 Parts List 27 CPS800 POWER SUPPLY RH MODULE ASSY Ident . [. . . ]