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PLL Board
HP 81 10A Service G
u
i
d
e
Thi s
b
oard co n s ists
m
ainly
o
f data-co ntrolled devices a nd
troubles h oot ing is r educed to repl acing suspect devices . H owe v er,
b as i c checks can b e
p
erformed on some
p
arts of t he circ uitr y:
On-Board
R
eg
u
lators
ι .
C
h eck U 205 pin 3
f
or -12 V
a
nd pin 1
f
or -5 .2
V
2 . Ch eck U 207 pin 3
f
or +12
V
a
nd pin 1 for +5 V
3 . C heck U 208 pin 3
f
or +32
V
and pin 2
f
or +23 .47
V
4 . C heck U 209 pin 2
f
or -12
V
a
nd pin 3
f
or -5 V
Cloc
k
Input
Wi th an external
C
l ock
a
pplied to J 401 :
1 . Ch eck
t
h at t he applied si gn al i s ±10 V. If not, ad
j
ust to ±10
V
2 . C h eck
t
h at t he sign al at the
j
un cti on
o
f R406 an d
R
407 is
app roxim ately ±2 .5 V. If not, suspect C R 402, C R 403, and
associated components
3 . Sel ect vari ou s Thres h old settings on t he instr um ent and ch eck t hat
v oltages are available
f
ro m U403 B pin 7,
U
403 A pin 1, and
U
404 B
pin 9
check th e relay Κ 401 as f ollo w s :
1 . On t h e in str ume nt select 50 Ω
E
xternal
C
l ock input
l
oad ing
2 . Co nnect t h e Scop e to
R
405 at t he end that connects to Κ401
3 . The re l ay sh ould
b
e closed; you will see the tr i gger w aveform
4 . B ri efly s h ort Q401 B ase to Emitter . The relay sho uld open
a
nd
t he scop e wav eform disappear while t he sh ort
i
s appli ed
Ch eck on Υ 251 pin 8
f
or 5 M Hz s ign al, if t he internal ref ere nce clock
i s
b
ein g
u
sed .
U
s in g the Scope check at U203 pin 5
f
or α
c
lock signal . If U 203 is
wor king, t his sig n al shoul d
b
e present, regardless of wh et her the
intern al or external referen ce c lock i s be ing used .
Ch eck at U204 B pin 7 for α contro l v oltage
f
or the varicap di odes
con tro llin g t h e
f
requen cy
o
f U201, t he PLL . Thi s should
b
e in t he
range -2.2
V
to +7.0 V, representing α PLL frequency range of 80
MHz to 160 MHz .
U
sing t he Scope, c h ec k for the PLL
o
utput signal
at
U
202 pin 2 .
Tr
ou
b
les
h
ooti
n
g 4-1 9
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