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P
erio
d B
oar
d
This
b
oard consists mainly of data-controlled devices and
troubleshooting is reduced to replacing suspect devices . However,
b asic checks can be
p
erformed . on some
p
arts of the circuitry :
Trigge
r
Input
With an external Trigger applied to
J
301 :
1 . Check
t
hat the applied signal is ±10 V . If not, ad
j
ust to ±10
V
2 . Check t hat the signal at the
j
unction
o
f R304 and
R
305
i
s
approximately ±2.5 V. If not, suspect C11301, CR302, and
associated components
3 . Select v arious Offset settings on the instrument and check t hat
voltages are available
f
rom U304A pin 1,
U
304D pin 14, and
U
301
pin 8
check t he relay Κ301 as
f
ollows :
1 . On the instrument select 50 Ω External Trigger input loading
2 . Connect the Scope to
R
301 at the end that connects to Κ301
3 . The relay should
b
e closed ;
y
ou will see the trigger
w
aveform
4 . B riefly short Q301 B ase to Emitter . The relay s hould open and
the scope waveform disappear while the short is applied
P
eriod Ge
n
erator
C
heck voltage regulators :
1 .
U
405 pin 1
f
or +12 V a nd pin 3
f
or +5 V
2 .
U
406 pin 1
f
or -12
V
and pin 3
f
or -5.2 V
TIG
ER
C
u
rrent So
u
rce
1 . Check voltage regulator
U
506 pin 3
f
or +12 V
2 . Check TJ506 pin 2
f
or +9 .2 V
HP 811 OA Service G
u
i
d
e
3 . Select various
P
eriod settings on the instrument and check that
v oltages are available from U504B pin 7 .
4 . Check that
U
504D pin 14 and
U
504C pin 8 mirror changes in
U504B pin 7 voltage . Chec
k
Q502 and Q503
Trigge
r
Outp
u
t
1 . Check that there is an input signal at the
j
unction
o
f R601 and
R
602
2 . Check that the input signal is available (inverted) at Q601
collector
3 . Check that the input signal is available (non inverted) at Q602
collector
4 . Check that an output signal
i
s available at Q604 collector
Tr
o
ub
les
h
ooting 4-1 7
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