EG&G ORTEC 442 Instrukcja obsługi i serwisowania - Strona 13

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CAUTION: if the Input switch is set to DC-Couple and the

output dc level of the Amplifier driving the 442 is not set

at zero volts, the 442 will appear to have a pedestal since

the 442 gate circuit wil l be chopping a dc voltage.

Discriminator Adjustment The 442 Disc Level should be

set wel l above the system noise because each pulse that

exceeds the discriminator level wil l be stretched, whether

it be noise or a legitimate signal. If the Disc Level is set far

below the system's noise, the 442 pile-up rejection circuit

may completely block the input and prevent any outputs

from occurring. Normally a discriminator level of 100 mV

Is adequate. A precise discriminator setting can be made by

the following procedure:

1 . Apply a 0.5-jUsec shaped signal to the 442 input with

amplitude equal to the desired Disc Level setting.

2. Monitor the 442 input and output signals with an

oscilloscope.

3. Adjust tne 442 discriminator control (front panel) unti l

the number of output pulses is approximately equal to one-

half the number of input pulses.

Tne discriminator is now properly adjusted.

6.3. SUGGESTIONS FOR TROUBLESHOOTING

In situations where the 442 is suspected of malfunction, it

IS essential to verify such malfunction in terms of simple

pulse generator impulses at the input. In consideration of

this, the 442 must be disconnected from its position m any

system and routine diagnostic analysis be perform.ed with

a test pulse generator and oscilloscope. It is imperative that

testing not be performed with a source and detector until

the amplifier-pulse stretcher system performs satisfactorily

with the test pulse detector.

The testing instructions in Section 6.1 of this manual and

the circuit descriptions in Section 5 should

provide

assistance in locating the region of trouble and repairing the

malfunction. The two side plates can be completely removed

from the module to enable oscilloscope and voltmeter ob

servations with a minimal chance of accidentally short-

circuiting portions of the etched board.

The 442 may be returned to ORTEC for repair service at

nominal cost. Our standardized procedure requires that each

repaired instrument receive the same extensive quality

control tests that a new instrument receives. Contact our

Customer Service Department, (615) 482-4411 , for shipping

instructions before returning the instrument.

if the problem involves an inabi l ity to get an output pulse,

there are several solutions:

1 . If Input switch IS in the DC-Couple position, switch to

Active. If output appears, a dc level is probably being

applied to the 442 input and locking up the pulse pile-up

circuit. Adjust the output dc level of the amplifier feeding

the 442 to zero volts.

2. Adjust the Disc Level fully clockwise. If an output

occurs, the discriminator was probably set below the

system noise level, locking up the pile-up circuit.

3. If operating in the Gated mode, switch to the Normal

mode. If an output occurs, the gating logic is probably not

in time coincidence with the linear pulse.

6.4. TABULATED TEST POINT VOLTAGES

ON ETCHED BOARD

The following voltages are intended to indicate the typical

dc voltages measured on the etched circuit board. In some

cases the circuit wi l l perform satisfactorily even though, due

to component variation, there may be some voltages that

measure outside the given limits. Therefore the voltages

given should not be taken as absolute values, but rather are

intended to serve as an aid in troubleshooting.

MOTE:

All voltages measured with no input and input

terminated in lOOfi. Input switch is dc-coupled and al l

potentiometers are fully clockwise.

Table 6.1. Typical dc Voltages

Location

Voltage

Location

Voltage

GIB

-I-

11 ,5

Q42C

11.9

QIC

-r 0,012

042 B

-1-

Q2B

11.5

0438

0.06

Q3B

0448

0.7

Q4B

0458

0.2

Q4C

■H

12.5

0468

-1-

0.4

Q6B

■F

0.6

0478

-I-

5.6

Q8G

048 E

0.78

Q8D

-K

18,9

0498

5.6

09 D

20.2

0508

0.15

one

■r

0.5

Q50C

0128

2.6

0518

-1-

1.1

Q12C

1 .6

051C

013D

-I-

17.6

Q52C

2.7

Q16E

18.2

Q53C

-I-

2.1

0178

2.3

0558

-1-

4 4

017C

■r

2.5

055 E

3,8

Q18E

0568

5.6

O20E

0.06

056C

-t-

021C

■r

22.1

0578

-r

0.4

022C

Q58C

-t

11 ,2

0238

2.4

IC-1

Pin 2

0258

3.8

IC-1

Pin4

Q28G

IC-1

Pin 7

0280

15,6

IC-1

Pin 3

-r

10,7

0220

-r

16.8

IC-2

Pin 3

1 ,3

030B

2.5

IC-2

Pin 8

-I- 0.05

Q30C

0.4

IC-2

Pin 9

-r

1 ,3

Q32C

0.012

IC-2

Pin'13

■r

0 ,1

039 B

■r

12.4

IC-5

Pin 8

0,1

0408

12.4

IC-3

Pin 8