CIRCUIT CARD/MODULE FUNCTIONAL DESCRIPTION

TM 32-5865-061-24&P

3-3. CIRCUIT CARD/MODULE FUNCTIONAL DESCRIPTION. The following subparagraphs

provide a functional description of the Receiver Set circuit card assemblies.

3-3.1 Buffer Amplifier CCA (A5) Functional Description. Refer to figure 3-3, a

f u n c t i o n a l bl o c k dia g r a m o f C C A A5 . T h i s CCA provides 5 MHz reference clock

T h e s e functions are

signals and monitors the fault status of the Receiver Set.

described in the following subparagraphs.

3 - 3 . 1 . 1 5 M H z R e f e r e n c e S i g n a l s . T h e 5 MHz REF clock signal is buffered by AR1

A R 3 provides the four 5 MHz reference signals for

a n d fed to drivers AR2 and AR3.

t h e r e c e i v e r s . A R 2 provides three 5 MHz reference outputs and the input to T1.

T 1 provides a 5 MHz differential sine wave output for system use. Buffer AR1 also

feeds 5 MHz REF to a level detector circuit U3. The circuit detects the presence

o f t h e 5 M H z s i g n a l . W h e n the signal falls below a preset level, comparator U3

provides current to operate relay K2. The normally open contacts of K2 close,

f e e d i n g +24V to the REF OSC FAILURE indicator lamp on the front panel.

3 - 3 . 1 . 2 E n c l o s u r e S t a t u s . C o m p a r a t o r U1 monitors the status of the temperature

s e n s o r c o n t a c t s . W h e n the contacts open, U 1 provides the current to energize

r e l a y K 1 . O n e set of contacts feeds +24V to the OVER TEMP indicator lamp on the

front panel. The other set of relay contacts grounds the input of line driver

U2 . U 2 also has as inputs fault status signals from A6, and relay K2 in the 5 MHz

r e f e r e n c e f a u l t d e t e c t o r c i r c u i t . W h e n a fault condition exists, U2 provides the

d i f f e r e n t i a l signal ENCLOSURE FAULT.

3 - 3 . 1 . 3 P o w e r S u p p l i e s . + 1 5 V and +5V are derived from the +24V supply by

r e g u l a t o r s VR1 and VR2.

These supply power for the integrated circuits on the

+ 1 5 V is fed out to Supply module Y1, and AR1 through AR4, mounted on the

card.

Receiver Set chassis.

3-3.2 Power Supply Monitor CCA (A6) Functional Description. Refer to figure 3-4,

a functional block diagram of A6. A 6 p r o v i d e s o v e r v o l t a g e p r o t e c t i o n f o r t h e

circuits and assemblies in the Receiver Set.

S i x crowbar devices U1 thru U6

m o n i t o r t h e p o w e r s u p p l y o u t p u t v o l t a g e s . T h e y operate when there is an over-

voltage condition short circuiting the power supply. This causes the overcurrent

protection circuit, part of each power supply module, to operate. The power

supply voltages are also monitored by opto-isolator devices U7 through U9 in

s e r i e s . When any one power supply voltage fails the appropriate device switches

o f f l a m p d r i v e r t r a n s i s t o r s Q 1 a n d Q 2 . T h i s condition causes the power indicator

lamp to go out and relay K1 is deenergized providing the POWER SUPPLY STATUS

signals.

3-4