Crown MARCO-TECH 5000VZ User Manual page 28

Notes
Fan Control
The MA-5000VZ, unlike other members of the Macro-Tech family, has
two on board fans. They are mounted to the chassis dívider assembly
and pulí cool air from the front and discharge it across the output stage
heatsinkstotherearoftheamplifier. Aíso unlike the other Macro-Techs,
the fans are fully ODEP proportional (opérate in proportion to output
stage temperature and calibrated ODEP control voltage).
U713B combines channel 1 temperature and ODEP level, U713A for
channe!2. D706andD707formad¡odeORgaíe. The output of the OR
gate drives one input to U707B. The other ¡nput to U707B is from the
DC pulse width control círcuit (U701B). U707B opérales in a fashion
similar to that of U707A, the Soft-start control amplifier. A graphic
example of the fan control waveforms would look a good deal like those
¡n Fig. 4.7, except that the thermal drive would be unique f rom that of the
Soft-start ramp.
The fans will aíso be forced to opérate at full speed in the event a toroid
transformer thermal switch trips open. Note that very early units did not
¡nclude this additional circuit.
+ 15V
U701B
LM339
To Fan
Control
Triac
R799
4.7K
-
U713A"
TL
°
72C
S731
-ftv
28 - MA-5000VZ