Troubleshooting
Servicing
Cable-TV incoming signal line (round, 75Ω) at the wall,
or the first component the cable is connected to (i.e. the
cable box, or VCR). If the hum is no longer present, you
must insert a “75Ω ground loop isolator” before recon-
necting the line. You should check with your ADCOM deal-
er to obtain one. If the “75Ω ground loop isolator” works
only partially or not at all, then please read note 2 to
complete the troubleshooting procedure.
Note 2:
Make sure that the power amplifier is at least 6”
from processor or other equipment using microprocessors.
Usually putting another component between them is suf-
ficient to minimize the hum. If this does not reduce the
hum, turn the system off and disconnect all Inputs from
the amplifier. If the hum still persists, then your dealer or
service center must examine the unit/system. If the hum
disappears, try another set of RCA cables. Connect one
RCA cable at a time to see if one specific cable is respon-
sible. If any or all cables cause the hum to appear, then
the unit should be evaluated for proper operation by your
dealer or authorized service center. Please see our website
for a list of authorized service centers in your area.
Hum can be caused by adding new components to your
system, but that does not imply there is anything electri-
cally wrong with any new component. With the advent of
audio/video and home theater systems, the problem has
become commonplace. Generally, the cause is the Cable-
TV incoming signal line. This new incoming line may add
an additional ground at a different potential to the AC
line ground of your other equipment (refer to note I and
2, to troubleshoot a hum problem).
ADCOM has a technical service department to answer
questions pertinent to the installation and operation of
your unit. In the event of difficulty, please contact us for
advice. If your problem cannot be resolved through our
combined efforts, we may refer you to an authorized re-
pair agency, or authorize return of the unit to our factory.
Note 1:
Cable TV systems can sometimes contribute to
ground loop problems which cause “hum.” To determine if
your cable system is the contributing factor, disconnect the
Use the troubleshooting notes above to solve common sit-
uations that don’t require professional attention. If the
steps stated in possible solution do not resolve your prob-
lem, then please contact your ADCOM dealer or call the
ADCOM customer service department. Any problems not
covered here should be brought to the attention of your
ADCOM dealer or ADCOM customer service department.
A special note on “hum:”
When there is a low-volume
“hum” audible throughout your speakers, even with the
main volume turned all the way down, you have a common
phenomenon known as a “ground loop.” A ground loop is
basically a difference in ground voltages between two or
more components which are connected electrically and
which creates multiple current paths where there must
only be one. This difference in potentials creates a 60Hz
low-level sound (approximately a low A), that seems to be
a “hum.”
SYMPTOM
POSSIBLE REASON
POSSIBLE SOLUTION
Power LED does not
glow. No sound
AC Power Cord(s) not plugged in. AC
Fuse(s) failed. Transformer thermal protec-
tion engaged. I2V DC triggering malfunc-
tioning.
Plug in AC Power Cord(s). Replace AC
Fuse(s). Wait until unit cools down. It will
reset. Reset power switch manually.
Check connection of 12V DC trigger at
source.
Power LED glows, but no
sound
Preamp or source unit is not on. Connec-
tions in rear of amp are loose.
Make sure whole system is on. Verify all
connections on rear of amp.
One channel not produc-
ing sound
INPUT(s) or OUTPUT(s) connector discon-
nected or loose. Speaker disconnected.
Internal protection engaged.
Verify both connections on that channel.
Verify connection at speaker. Bring to
Dealer or Service Center.
Hum from all speakers
at any volume
Ground loop (difference in ground voltages
between components).
If Cable TV is present (see Note 1). If Ca-
ble TV is not present (see Note 2).
Hum from all speakers
(hum goes up or down
with volume)
Problem with source unit (CD, tape, etc.),
or RCA cable connecting that source unit to
the preamp.
Try different source (tuner, tape, etc.)
and/or different RCA cable.
Hum from the amplifier
itself
Some major appliance, dimmer, halogen or
fluorescent light is creating interference.
Make sure all appliances, dimmers and
suspect lights are off.
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