Model34904

tion drawing).Connectthe gatesof both A2QIA and B to ground. Connecta dc null meter (-hp- 419A) between AITPR and ground, and adjust AlR522 from one extreme to the other. If this point adjustsboth positive and negative, the amplifier is probably operating cor- rectly, and the BootstrapAmplifier shouldbe checked. If AITPR will not adjust both positive and negative, connect the dc null meter betweenthe sourceof A2Ql B and add adjust AlR522 Io both extremes.The voltage should adjust both positive and negative.Each stageof the amplifier can be checked in the same manner, connecting the dc null meter between the collectors of A1Q509A and B, the emittersof A1Q505andAlQ508, the collectorsof AlQ506 and AlQ507, or the emitters o f A l Q 5 1 0a n dA l Q 5 1 1 .

TRIGGER SCOPE AT A] . TPK, + SLOPE . C H E C K W A V E F O R M S T O S E E O N L Y I F

. 1 7 V A N D . 2 0 V L E V E L S O C C U R A T

T H E C O R R E C T T I M E S . D U R I N G A L L O T H E R I N T E R V A L S , W A V E F O R M S SHOULD COR RESPOND TO THE BOOT . STRAP VOLTAGE .

TIME {ß1 .

& 1 & t i l

&2 AAiGE

- t 7 v

1A t L

2. 5 A L t

30 . t , 1 , r m r

3t o , r K V

a t @ , t K v

r 0 0 . 1 ,r , 1 0 v

1 6 A T L

' t

J

1 9 A T L

2I ALL

23 0 _ l v

T I M E S H O W N A P P L I E S T O I N S T R U .

M E N T S D E S I G N E D F o R 6 0 H z L I N E

O P E R A T I O N . F o R 5 0 H z I N s T R U -

M E N T s , I N C R E A S E T I M E B Y 2 O O I O .

Figure7-1. SwitchingInputsto A2U2.

SectionVII

T R I G G E R S C O P E A T A 1 T P K , + S L O P E .

Alu401

6

nlii,,,

0 . 1 ,t . t 0 v

1 0

t t

12

13

1 7

t8

l 9

20

2 1

0 . 1 ,t . 1 0v

'4 e o a - a ' 2 s 4 6

*T I M E s H o w N A p p L l E s r o T N S T R U M E N T S

D E S I G N E D F O R 6 0 H z L I N E o P E R A T I o N .

F O R 5 0 H z I N S T R U M E N T S , I N C R E A S E

TIME BY 2Oolo .

Figure7-2. SwitchingOutputsof A1U401.

7-21. After these checksand following repair of the DC Amplifier, the DC Amp. Zero control shouldbe adiusted usingthe following procedure:

a.'Set 3490A FUNCTION to TEST, RANGE to 2, SAMPLE RATE to FAST.b.Connecta clip leadacrossA2C3.c.Adjust AlR522 for a display of +.000010 to

-.000026.

'l-22. DCAmplifierSwitchingGircuits.

7-23. Figwe 7-l shows the inputs to the DC Amplifier input switching FET'sWaveforms.at the connections to

A2U2 shouldbe comparedto the bootstrap waveform at the white jumper on A2 (labeled"Bootstrap" on the

Component L.ocationdrawing). The "OFF" voltagelevel of - l7 V or - 20 V must be correct. During the ..ON"

time, when the waveform is more positivethan - 17 V, the waveform should correspond to the bootstrap waveform.

7-24. The switching outputs of the DC Logic ROM, shownin Figure7-2,shouldbe asshownin eachcase.

t-3