SoundCraft CPS2000 - Manual (Page 25)

Setting Setting Voltage Spec’d Measured
EUROPE 230/115 230 195 186
EUROPE 200/100 200 170 164
USA/JAPN 230/115 115 98 95
USA/JAPN 200/100 100 85 85
Note that the dropout voltages in the rightmost column were measured on a CPS2000,
and are significantly lower than the guaranteed dropout specification of -15%.
Fan Control PCB. SC4032.
Thermostatic fan control was fitted to the CPS2000 from February 1999. The
controller is a separate PCB (SC4032) mounted on the front heatsink bracket, with a
thermal sensor pressed against the top surface of the heatsink.
The CPS2000 fan control system adapts the fan speed to the power drawn. This gives
a substantial reduction in fan noise under almost all circumstances; the exception being
10% high mains and maximum current drawn, which naturally sets the fan to full
speed. The PCB (with associated mounting bracket) may be retrofitted to existing
CPS2000 units.
The servo circuit consists of opamp IC1-A, temperature sensor IC5, shunt regulator
IC4, and fan control devices TR7,TR10.
IC4 maintains 2.50V between its "anode" and "cathode"; this is the precise voltage
that drives the reference chain R53,55. TR8 also uses this voltage to set its emitter at
4.4V above ground; this keeps IC1’s inputs within their common-mode range. Thus
both ends of the voltage divider R53-R55 are fixed at defined voltages.
LM35DZ temperature sensor IC5 outputs 10mV per degreeC above freezing point (0
degC) and applies it to IC1-A non-inverting input. The desired heatsink temperature
is set at the junction of R53,55, which sits at +5.0V approx. This is 600mV above the
+4.4V rail, and so represents 60 degC.
R52,57 set the servo loop gain. This is designed to be safely below the level at which
slow thermal oscillations would occur. R56,D19 increase the loop gain when IC1-A
output is below 4V. This prevents the fan sitting for long periods in a not-quite-running
state where it consumes current but does not rotate. The voltage range 1-4V where
this occurs is thus skipped over quickly.
The fan is driven through feedback amplifier TR7,10, which has a voltage gain of 1.3
times. This allows the fan to be driven over its full operating voltage range despite the
output saturation limits of IC1-A. This gives improved cooling at high temperatures
and mains voltages.
The CPS2000 thermal shutdown system is quite separate and has no connection with
this PCB.
Circuit Description 21