EG&G ORTEC 775 Manual de operação e serviço - Página 11

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in LED 3 to display that digit. When IC 16 is advanced to a

state of 6, the decade is reset to zero through IC 22-3 and

IC 22-6 to start the scan again.

The four common l ines wi l l carry the BCD identification

for the selected decade into IC 17, which decodes the digit

for the 7-segment LED 3 character that is enabled by the

selection of IC 8. When al l seven segments of a character are

lighted, a digit 8 is formed in the display. Selective blanking

of the segments a through g forms any of the other 9 digits.

Segment a is across the top of the character, with segments

b through f clockwise around the border and segment g

across the center. When switch SI is pressed, al l seven

segments of al l characters are lighted for a test of the

display. IC 21-3 and IC 21-6 provide blanking for insignifi

cant zeros in the display.

(Local Reset) signal resets all counting decades to zero,

restores the flip-flop for LED 2 if it had been set during the

prior counting interval, inhibits acceptance of any input

pulses and turns off LED 1 through IC 20-12, and inhibits

the generation of an Overflow output pulse by the response

through IC 23-6.

5.5. INTERNAL POWER SUPPLY

An internal power supply is included to generate the +5-V

source for the integrated circuits. 115 V ac is applied to T1

and ful l-wave-rectified by D4, fi ltered by C18 and C19, and

regulated by Q18 through Q20. Fuse F1, 1.5 A, is mounted

in a fuseholder on the printed circuit board. The fuse

protects the +5-V source from overloads due to shorts in

the instrument.

5.4.

RESET CIRCUIT

The 775 can be reset at any time by either pressing switch

S2 on the front panel or by furnishing a reset input pulse

through CN5 on the rear panel. Either of these conditions

makes IC 20-6 go high during the reset signal. The LR

The 775H Counter does not contain the portion of this

power supply that consists of T1, D4, C18, and C19. It

obtains its +5-V power from the +6-V source in the

ORTEC 401 B/402FI Bin and Power Supply. In this version

the collector of Q20 is connected to pin 10 of the rear

panel module power connector.

MAIIMTEIMANCE

6.1. GENERAL

The basic performance of the 775 Counter can be tested by

following the procedure outlined In Section 4.2. This wil l

not check the unit to its published specifications.

If the unit fails to respond properly during testing, use the

information in Section 5 to determine the fault. Schematic

775-0101-S1 at the back of the manual includes al l the

circuits in the unit.

6.2. FUSE REPLACEMENT

If the front panel display and indicators cannot be lighted,

remove the left side panel and inspect fuse F1. This fuse

protects the +5-V power source that is used for al l the

integrated circuits in the instrument, and the Indicators

cannot be lit unless the Integrated circuits are operating.

Replace the fuse with a type SAG fuse with a 1.5-A rating

only.

6.3. FACTORY REPAIR

The 775 can be returned to ORTEC for repair service at a

nominal cost. Our standard procedure requires that each

repaired instrument receive the same extensive quality

control tests that a new instrument receives. Please contact

our Customer Service Department at (615) 482-4411 for

shipping instructions before returning the instrument.