Adcom GFA-7700 owner manual Troubleshooting, Resolving Problems

Troubleshooting

Resolving Problems

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.

Symptom	Possible Reason	Possible Solution
Power LED does not glow	AC Power Cord (3) not plugged in	Plug in AC Power Cord (3)
No sound	AC Fuse (4) blown	Replace AC Fuse (4)
	Transformer thermal protection engaged	Wait until unit cools down-it will reset
Power LED glows,	Preamp or source unit is not on	Make sure whole system is on
but no sound	Connections in rear are loose	Verify all connections on rear of amp
One channel not	Input (1) or Output (2) connectors	Verify both sets of connections on that
producing sound	disconnected or loose	channel
	Speaker disconnected	Verify connection at speaker
	Internal protection engaged	Bring to Dealer or Service Center
Hum from all speakers	Ground loop (difference in ground	If cable TV is present (see Note 1)
at any volume	voltages between components)	If cable TV is not present (see Note 2)
Hum from all speakers	Problems with source unit (CD, tape,	Try different source (tuner, tape, etc.)
(hum goes up or	etc.) or RCA cables connecting that	and/or different RCA cable
down with volume)	source unit to the preamp
Hum from the amplifier itself	Some major appliance, dimmer, halogen or	Make sure all appliances, dimmers and
	fluorescent light is creating interference	suspect lights are off

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.

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