Behringer A500 thumping in one channel - diyAudio
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Old 23rd November 2010, 09:17 AM   #1
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Default Behringer A500 thumping in one channel

Hi, A Behringer A500 amp has the following conditions;
The right channel has a loud thump noise and the led indicators pulse full scale about once per second. This happens if there is OR isn't a audio input present, but only happens when the main gain control is set almost full. I have a circuit diagram. Have replaced the electrolytics C31, C28, C39 and the non-polarized cap C34, but still the same. I suspect the amp IC4b - will replace it when spares arrive. This channel also has a lower audio output than the left channel.

Question is; Can anyone explain the bias pots adjustment procedure. I have not touched the pots, but would like to know what voltages at what points, should be measured when the pots are set correctly.

I also noticed that 2 resistors R71 and R72 are shown (voltage divider) in the diagram, but are not fitted on the board.

Any help will be greatly appreciated. Thanks
DigAudio
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Old 10th December 2010, 10:48 AM   #2
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This amp is now back to its former glory! Replaced the op-amp (SMD) and problem solved. Much happiness!!!
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Old 18th June 2013, 12:55 AM   #3
Rossgo is offline Rossgo  Australia
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Hi

I have the same issue in channel B . I have ordered replacement 4580M op amps . I'll keep you posted on how it turns out .
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Old 29th June 2013, 02:36 AM   #4
Rossgo is offline Rossgo  Australia
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I injected 1KHz into the RCA input , and used a scope to trace the signal. I Only got to IC4(b) 4580M op amp, The output had gone high (+15V DC) . Replaced it and now is working well.
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Old 29th June 2013, 02:39 AM   #5
Rossgo is offline Rossgo  Australia
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I injected 1KHz into the RCA , traced it with a scope , found IC4(b) 4580M Op amp had gone high (+15v) . Replaced it an now it's working well
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