User manual SOUNDCRAFT CPS2000

[. . . ] SOUNDCRAFT CPS2000 Console Power Supply User and Technical Manual For your own safety and to avoid invalidation of the warranty all text marked with these Warning Symbols should be read carefully. IMPORTANT: please read this manual carefully before connecting your Soundcraft console power supply to the mains for the first time. © Harman International Industries Ltd. 1997, 2005 All rights reserved Parts of the design of this product may be protected by world-wide patents. Part No. ZM0198-05 Soundcraft is a trading division of Harman International Industries Ltd. Information in this manual is subject to change without notice and does not represent a commitment on the part of the vendor. [. . . ] 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. OPTO1 is on so the base drive to TR22 is shunted away and the 723 works normally. If either supply fails there is insufficent voltage to keep DZ8 conducting, and current flow ceases in the mutual shutdown line. TR22 is turned via the special supply generated by D13, C26, and the internal node of the 723 IC3 is pulled down to ground, turning it off. Likewise, in the -17V supply, TR28 is turned via the special supply generated by D14, C25, and the internal node of IC4 is pulled down to ground, turning it off. C27, 30 delay the action of mutual shutdown sufficiently to allow the supplies to start, as they may not rise to working voltage at exactly the same rate. Circuit Description 17 When shutdown has ocurred, the supply is reset by turning the mains briefly off and on. R100 discharges C25 so that the circuit is ready for use at the next switch-on. The special supplies generated by D13, C26, and D14, C25, are designed to discharge very quickly at power-off, and it should not be necessary to turn the PSU off for more than a second to reset it. Overcurrent Protection. The simplest form of overcurrent protection is the constant-current system; when an attempt is made to draw excessive current, the output voltage is reduced so that no more than a fixed maximum can be drawn. The high current capability of this PSU means that constant current protection alone is not practical as the dissipation in the pass devices is too high for the cooling system to deal with, and in the long term they will overheat. Once again the output voltage is reduced to prevent excessive current flow, but it is more severely reduced so that the current flowing is not limited to a fixed maximum, but to a value lower than that which triggered the protection originally. This greatly reduces the dissipation in the supply in protection mode. This system accomplishes its task, but can give trouble as the supply may work perfectly into a resistive test load but not start into a real console load. The problem is that a mixing console is essentially a constant-current load; as the supply voltage is increased, almost the full current is drawn when only 2 or 3 volts are applied. There are thus two stable states, with rails normal and the full current drawn, or with the supply shut down to the few volts that will cause the foldback current to flow. When the supply is switched on, it tends to stick in the second of these two states. The CPS2000 avoids this problem by implementing constant-current protection that causes complete shutdown (rather than foldback) after a fixed time delay. This is described for the +17V supply; the -17V supply operates identically. The first part of the problem is to measure the output current without dropping 0. 6V across a resistor to turn on a protection transistor. Therefore supply current is measured by the voltage drop across 0. 05R resistors (R35, 36 in parallel) which carry a quarter of the output current and so drop 200 mV at full load. This is compared with a 200mV reference voltage across R86, derived from bands-gap reference IC8 which sits on the output rail, by differential amplifier TR18, 19. [. . . ] TO3 INSULATING WASHER D7 (on SC3804-09) REG1 REG2 TR4 TR5 TR6 TR7 TR8 TR17 W/Form . TO3 INSULATING WASHER D8 (on SC3804-09) REG3 TR11 TR12 TR13 TR14 TR15 W/Form . PSU EARTH SYMBOL SLF-ADH 28 Parts List PCBS CPS2000 FAN CONTROL PCB ASSY Ident . CPS2000 FAN CONTROL PCB C1 CN1 D19 IC1 IC4 IC5 P1 P2 R32 R33 R35 R36 R38 R52 R53 R55 R56 R57 R58 TR7 TR8 TR10 TR10 . [. . . ]