FAULT
FINDING
©
Cyrus
Audio
Ltd
Jun
2014
14
Cyrus
6
DAC,
Cyrus
8
DAC
service
manual
Issue
1
Re
‐
testing
the
amplifier
after
repair.
After
repairing
the
amplifier,
connect
a
DVM
to
monitor
the
quiescent
current
in
the
repaired
channel.
As
you
switch
on
from
Standby,
watch
the
DVM
reading
which
should
read
just
a
few
mV
maximum.
A
high
or
rapidly
climbing
quiescent
reading
will
probably
indicate
that
a
fault
still
exists
within
the
power
amplifier
stage.
In
this
case
the
amplifier
should
be
switched
off
immediately
to
avoid
further
damage.
If
the
quiescent
remains
low,
then
proceed
to
set
the
quiescent
current
accurately,
referring
to
the
correct
section
in
this
service
manual.
If
the
quiescent
current
sets
correctly,
continue
to
check
and
set
the
DC
offset
voltage
at
the
speaker
terminals.
If
both
quiescent
current
and
DC
offset
settings
are
stable
at
the
correct
values,
proceed
to
connect
speakers
or
dummy
loads
and
check
the
function
of
the
amplifier
with
a
signal.
Preamplifier
faults
Power
supplies.
Before
commencing
any
fault
tracing
it
is
advisable
to
refer
to
the
preamplifier
schematic
sheet
and
check
the
power
supplies
to
each
of
the
preamplifier
ICs.
In
the
event
of
a
power
supply
failure,
trace
the
power
supplies
to
the
preamplifier
using
the
schematics.
Note
that
power
to
the
preamplifier
regulators
is
routed
via
the
PSX
‐
R
switching
circuit
T401/T402/T405/T406
when
a
PSX
‐
R
is
not
connected.
No
signal.
If
the
power
supplies
check
out
OK,
then
pre
‐
amplifier
signal
faults
are
best
found
by
supplying
a
sine
‐
wave
signal
to
the
amplifier
inputs
and
tracing
this
through
the
pre
‐
amplifier
stage
input
selector
and
volume
ICs
to
the
power
amplifier,
and
replacing
any
components
where
the
signal
may
be
lost.
The
Zone
2
output
can
help
trace
signal
faults.
If
the
test
signal
can
be
seen
at
the
Zone
2
output,
but
not
at
the
Pre
‐
amp
output,
then
the
volume
control
IC100
or
input
selector
!C101
may
be
faulty.
If
there
is
no
signal
at
the
Zone
2
output,
then
the
Zone
2
selector
IC102
may
be
faulty.
Control
system
faults
If
the
front
panel
does
not
power
up
and
set
to
standby
when
power
is
applied,
then
test
the
control
system
power
supply
as
described
in
the
‘Initial
precautions
and
first
tests’
section.
If
the
front
panel
initialises
and
sets
to
standby,
but
there
are
problems
with
any
element
of
the
control
system
the
front
panel
control
PCB
will
require
replacement.
If
one
of
the
control
keys
is
not
operating
correctly,
then
check
that
the
switch
operates
mechanically
and
that
it
is
not
sticking
in
the
technical
moulding.
Digital
audio
faults
If
a
fault
is
suspected
with
a
digital
input
sub
PCB,
some
initial
diagnostic
work
is
worthwhile
before
removing
the
PCB
as
this
cannot
be
powered
for
tests
once
it
is
removed
from
the
amplifier.
Connect
a
digital
input
to
one
of
the
electrical
or
optical
inputs
of
the
amplifier.
Select
this
input
and
check
if
the
sample
rate
is
correctly
indicated
on
the
display.
If
the
sample
rate
reads
OK,
this
suggests
that
the
digital
input
IC
(IC701)
is
working
correctly.
Check
the
other
digital
inputs
in
the
same
way.
The
USB
input
may
be
checked
by
connecting
a
computer
as
a
source
with
an
audio
signal
playing.
If
all
digital
inputs
are
working,
but
USB
is
not,
then
the
USB
decoder
IC601
or
one
of
the
associated
components
may
be
faulty.
If
the
input
selector
IC
is
working
for
all
inputs,
then
check
both
left
and
right
channels
at
the
audio
output
of
the
amplifier
using
one
of
the
digital
inputs
as
a
source.
If
one
or
both
of
the
