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HP 811 OA Service Gui
d
e
Vern ίeΓ Currents
*Select v ari ous Amplit ude sett ings on the instrument and check
th at
v
oltages are avail able
f
rom U300 pin 1 (high imp eda nce) and
U
302 D pin 14 *Check t hat U 302c pin 8,
U
302A pin 1 and
U
302 B pin
7 mirror ch an ges in U 302 D pin 14 vol tage . C heck Q302, Q303 and
Q304
A
mp
lifier
The ampli fier
i
s fitted to t he O u t pu t B oard in "piggy-b ack"
m
anner.
I
t i s an S MT b oard and the re are no recommen ded tro ublesh oot ing
p roced u res, except to c heck t he signal at th e inpu t and
o
utput .
S i gn al input
p
oints are at
J
701(1) an d
J
701(2).
S i gn al
o
u t put
p
oints are at J 702 (6, 8, 10) and
J
703 (6, 8, 10) .
Th e rep a i r o f t h e Amplifier is outs ide t he sco pe of this
T
ro ubles h oot ing g ui de as any changes to comp o nents would affect
calib rat i o n . and it is recomme nded that the complete Out put Board
b e ret urn ed to α
H
e wlett- Pac
k
ard Ser vice Center .
Outp
u
t Control
Q400, Q402, Q403 an d Q405 form th e cascode out put stage driv en by
the amplifier .
Th e cascode has α doubl e heatsink arrangement . You can r un t he
b
oard wi th
t
h e first h eatsink removed, but
n
ot th e second one, whi c h
takes the
f
orm
o
f α
m
ount ing plate
f
or the devi ces .
B ase an d collector voltages on these transistors should
b
e ±21 .5 V
Offset Control
1 . Se l ect v ari ou s Offset settings on th e instrument and check th at
v oltages are available
f
rom U 500 pin 1 (high impedan ce),
U
510 B
pin 7, and t h e emitters of Q500 and Q501
2 . C h eck t hat
U
502A pin 1 and
U
502 B pin 7
f
oll o w U501 B pin 7
v oltage chan ges
3 . C h eck
t
hat
U
503 A pin 1 and
U
503 B pin 7
f
oll ow U501B pin 7
v oltage chan ges
4 . C h eck transistors assoc iated with this circuit
O
u
tp
u
t Enable
1 . C h eck
t
hat o utput signal s are available
f
rom U600C pin 8 and
U
601 B pin 7 .
2 . C h eck U 602
Tro
ub
les
h
ooting
4- 23
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