SoundCraft CPS275 - Manual (Page 22)

FAULTFINDING NOTES.
+/- 17V RAILS.
If one side of the +/-17V supply is not working, the mutual shutdown system will
close down both sides of the supply. This makes faultfinding difficult as it is often not
obvious which side has failed. The mutual shutdown can be disabled by linking pins
4 and 5 on BOTH opto-isolators
IT IS ESSENTIAL THAT THIS IS REMOVED AFTER SERVICING IS
COMPLETED! FAILURE TO DO THIS MAY CAUSE SEVERE CONSOLE
DAMAGE IF ONLY ONE 17V RAIL SHUTS DOWN.
If there is no power to the 723 IC (eg if R1 or R2 is open- circuit) the output will
remain low, but no damage occurs.
+8V SUPPLY.
This is a completely standard IC regulator circuit. The regulator REG3 is the only part
that is likely to fail.
REPLACING COMPONENTS
Replacement of any components should be
undertaken only after switching the power supply
unit OFF and disconnecting the mains supply lead
from the power supply unit.
Replacement of any of the fuses in the power supply units is possible without the
removal of the circuit board.
The fuses are held in open fuseholders on the top of the board. These can be carefully
removed by hand. Ensure that the insulating fuse covers are replaced with the new
fuses.
Various components are mounted along the heatsink extrusion. The extrusion/pcb
assembly must be removed from the case to gain access to the underside of the pcb in
order to unsolder and/or undo the appropriate component. They can be removed by
desoldering the pins, where appropriate, and unscrewing the fixing nuts or the fixing
screws, taking care to retain the small insulating bush(es).
Retain carefully the mounting pads and plastic insulating bushes where fitted.
THESE MUST BE CORRECTLY REFITTED TO AVOID DAMAGE TO THE
UNIT.
The correct high efficiency mounting pad must be used, and this should be replaced
if it appears to be damaged (see the Parts Lists for the relevant Soundcraft Part
Numbers). When refixing or replacing the device, it is important to screw the device
down before resoldering the pins to avoid stressing the pads on the circuit board.
NOTE : The heatsink bracket is earthed through
its mechanical contact with the rest of the chassis
and so a faulty mounting pad may cause the output
of its regulator to be connected to earth.
Take care not to bend the pins on the regulators, or
to strain the corresponding pads on the circuit board
18 Technical Description