Adcom GFA-7400 - Advanced Troubleshooting Techniques; Cable TV Hum Isolation Method; Component Placement and Cable Testing

/Vote t : 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, 75Q) 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 “750 Ground Loop
Isolator” before reconnecting the line. You should check with your Adcom Dealer to obtain one. If
the “750 Ground Loop Isolator” works only partially or not at all, then please read Note 2 to
complete the troubleshooting procedure.
/Vote 2 : Make sure that the power amplifier is at least 6” 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 one specific
cable 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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