STANDBY BATTERY SUPPLY , 1A8

TM 11-5820-917-13

4-52. CRT DISPLAY (1A7) . The CRT display is a standard raster TV moni-

tor consisting of a cathode ray tube and drive electronics in a replaceable module.

The CRT is sealed to protect it from shock and vibration and to minimize possi-

bility of arcing for airborne operation. The CRT display drive circuit provides

video input amplification, raster trace waveform shaping, and yoke drive cur-

rent. In addition, the circuit provides adjustments whereby various parameters

(e. g. , brightness, width) can be manually controlled to counter effects of tube

and component aging. The timing relationships for the CRT display are depicted

in figure 4-6. Note that the raster is turned 90 from what is normally expected

on a display tube. The CRT operates from a single +12 VDC supply and generates

all other required supplies (+26V, - 120V, +340V, and +9kV) from its own trans-

former (T 1) .

4-53. STANDBY BATTERY SUPPLY , 1A8

4-54. Either one of two different types of standby battery supply assembly is used

in the RC S-4B. Some receivers have a non-rechargeable battery supply (P/N

6025- 1008) that uses standard D-cell batteries. Other receivers have a recharge-

able supply (P/N 6025- 1018) that includes an integral charging circuit and uses

sealed lead acid cells. Different checkout procedures are used for the supplies

and are described in paragraph 5-15.

4-55. NON-RECHARGEABLE SUPPLY (P/N 6025- 1008). The non-rechargeable

battery consists of 18, 1. 5-volt batteries. The supply (approx. 29 to 15 volts

depending on battery condition) is used to drive the swtiching regulator and the

crystal oscillator located in the frequency standard module 1A 3 if the main power

is interrupted. A test circuit, located on the programmer circuit card 1A 2A 1,

measures the output voltage of the battery supply and yields the results necessary

to drive the front panel indicators. A 5-amp fuse, located within the supply, pro-

vides protection for inadvertent shorts.

4-56. RECHARGEABLE SUPPLY (P/N 6025-1018) . The rechargeable battery supply

( figure FO- 22) is used to maintain timing synchronization, blanker frequency

memory and the 5 MHz frequency standard in the event of power cut-off. The

supply consists of 12 sealed lead/acid batteries, rated 2-volts each, and a voltage

regulator circuit card. The supply is contained in a sliding drawer. Standby

power of 28-volts DC is supplied to the 5 MHz frequency standard and to a switch-

ing regulator which provides +5 volts DC to the programmer timers.

4-57. The regulator card, mounted in the battery box, receives unregulated +35

VDC input from the 4028 power supply. Voltage regulator U 1 (figure FO- 22) is

set to output exactly 28.9 VDC by potentiometer R 3. The resulting 28.9 volts at

TP1 provides a precise terminal voltage ( 28.2 volts) for the batteries at the manu-

facturers recommended trickle charge rate of approximately five milliamps. The

6.8 ohm resistor, R4, limits the charging current to a safe value ( 400 mA max. )

when the batteries are discharged. The 2-amp fuse, F2, prevents severe physical

damage to the system wiring harness or battery box if an inadvertent short occurs

on the 28 volt line. Fuse FI protects the 4028 power supply from shorts in the

battery charging circuit. Permanent damage to the batteries may occur if they are

allowed to completely discharge to 0 volts. Relay coil (K 1) and zener diode ( VR 1)

sense the battery voltage. If the voltage drops below 17 volts, relay K 1 drops