Adcom GFA-7700 사용자 설명서

Use the chart below to solve common situations that don’t require professional attention. If 

the steps stated in POSSIBLE SOLUTION do not resolve your problem, 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 “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 potential 

creates a 60 Hz low-level sound (approximately a low A#), that appears to “hum.”

It can be caused by adding new components to your system, but that does not imply there 

is anything electrically 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 from the AC line ground of your other equipment.

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 Cable-TV incoming signal line (round, 75Ω) at the wall, 

or the first component to which 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 reconnecting the line. You should check with your 

ADCOM Dealer 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 six inches from the Preamp and/or Processor. Usually putting 

another component between them is sufficient 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 amplifier. If the hum disappears, try another set of RCA cables. Connect one RCA cable at a time 

to see if the specific cable or component is responsible. If any or all cables cause the hum to appear, then the 

preamp or processor should be evaluated for proper operation by your Dealer or Authorized Service Center.

13

  Symptom

 

  Power LED does not glow

  No sound

 

 

  Power LED glows, 

  but no sound

 

  One channel not

  producing sound

 

 

 

  Hum from all speakers

  at any volume

 

  Hum from all speakers

  (hum goes up or 

  down with volume)

 

  Hum from the amplifier itself

Possible Reason

AC Power Cord 

(3) not plugged in

AC Fuse 

(4) blown

Transformer thermal protection engaged

Preamp or source unit is not on

Connections in rear are loose

Input 

(1) or Output (2) connectors

disconnected or loose

Speaker disconnected

Internal protection engaged

Ground loop (difference in ground 

voltages between components)

Problems with source unit (CD, tape, 

etc.) or RCA cables connecting that 

source unit to the preamp

Some major appliance, dimmer, halogen or 

fluorescent light is creating interference

Possible Solution

Plug in AC Power Cord 

Replace AC Fuse 

Wait until unit cools down-it will reset

Make sure whole system is on

Verify all connections on rear of amp

Verify both sets of connections on that 

channel

Verify connection at speaker

Bring to Dealer or Service Center

If cable TV is present (see Note 1)

If cable TV is not present (see Note 2)

Try different source (tuner, tape, etc.) 

and/or different RCA cable

Make sure all appliances, dimmers and 

suspect lights are off