HughMongus
New Member
I have a Marantz 2230 that I have been working on. After recapping, the power amp has found to have a problem. It now has a mild scratchy noise upon power-up and power-down. Only one channel has this noise. That one channel still amplifies but is a bit distorted even when played through unenclosed utility speakers.
Conditions:
Amp segregated from all other circuits except the power supply which measures and scopes out just fine.
Amp loaded with 8 ohms or open produces the noise. No noticeable change in the noise on a scope.
No notable frequency content the noise, just splatter.
Amplifier can't hold center voltage at J758. Seems to start there but, drifts down to 2 volt range in 5 seconds producing the noise all the way down. Once at 2v, the noise ceases and the distortion kicks in (due to clipping the bottom of the waveform?). Upon power down the distortion fades and the noise comes back as the caps drain. Voltage at J758 even drifts back up to midsupply briefly before totally drained.
The noise appears on the open input to the power amp (J751). I don't see a clear feedback loop there.
Behavior much the same when connected to the preamp (J006 jumpers installed) using any input.
Most every node in that power amp except power (J755) and ground (J762) has some variation of this noise on it.
The power amp circuitry to limit the current in the output transistors seems to be functioning. They warm when loaded but not hot. The transistor H004 between the output (J758) and ground gets warmer of course.
Should not matter but.... the switches and pots were cleaned, the dial lights went from incandescent to LED and all the decades old solder rosin was removed from the circuit boards.
Never had this much difficulty with a recap before. Something is at work here and I am not seeing it. Any thoughts on this will help. Thanks in advance.
Hugh
Conditions:
Amp segregated from all other circuits except the power supply which measures and scopes out just fine.
Amp loaded with 8 ohms or open produces the noise. No noticeable change in the noise on a scope.
No notable frequency content the noise, just splatter.
Amplifier can't hold center voltage at J758. Seems to start there but, drifts down to 2 volt range in 5 seconds producing the noise all the way down. Once at 2v, the noise ceases and the distortion kicks in (due to clipping the bottom of the waveform?). Upon power down the distortion fades and the noise comes back as the caps drain. Voltage at J758 even drifts back up to midsupply briefly before totally drained.
The noise appears on the open input to the power amp (J751). I don't see a clear feedback loop there.
Behavior much the same when connected to the preamp (J006 jumpers installed) using any input.
Most every node in that power amp except power (J755) and ground (J762) has some variation of this noise on it.
The power amp circuitry to limit the current in the output transistors seems to be functioning. They warm when loaded but not hot. The transistor H004 between the output (J758) and ground gets warmer of course.
Should not matter but.... the switches and pots were cleaned, the dial lights went from incandescent to LED and all the decades old solder rosin was removed from the circuit boards.
Never had this much difficulty with a recap before. Something is at work here and I am not seeing it. Any thoughts on this will help. Thanks in advance.
Hugh