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HP 811 OA Service Guide
1. C h eck
t
h at
n
e ither of the t wo LED s are illumin ated ( D S401 and
D
S402 in Fig ure 4-4) . Thi s s ituati on is co vered by the flo w chart in
Fi gure 4-3
2 . disconnect
m
ain s
p
o w er an d check that the
f
ans are phy si cally OK
-
f
ree
f
ro m damage or obstruct ion
3 .
U
sin g an O hmmeter chec k for < 1 Ω continui t y: t he
m
ain fuse,
FH401, indu ctor LP 401, swi tch 5401, filter FL 401 and t he
m
ains
ca bl e, inclu d ing any fuse fitted in
t
he p o wer plu g .
T
riac
D
401 supp resses
l
o w imp edance voltage
p
eaks on the supply
line . If thi s tr iac
f
ail s, it
m
ay not
b
e imm edi ately not icea bl e, but
test- b en ch fu ses
m
ay fail if high line voltage
p
eaks occur during
high
c
urren t operation
o
f t he HP 8110 Α.
After t hese
p
reli min ary
c
hecks cont inue by
c
hecking wh eth er th e
oscillator
i
s o p eratin g.
oscillato
r
Α PWM (Pul se Wi dth Mo dul ation) oscill ator provi des driv e
for Τ401 Α , t he transformer . Ass uming that the regul ators are
n ot fun cti o nin g correct ly , the first check is t hat t h e oscillator i s
fun ctioning .
P
roceed as foll ows :
1 . Set th e Scop e to 500
V
D
C
2 . Connect th e Scope to CR407 an ode (see Figure 4-4 for co nnexion
p oint) .
3 . Ch eck
t
h at the observed waveform s are similar to t hose sho wn in
Fig u re 4-6
T
r
o
ub
les
h
ooti
n
g
4-9
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