Post by nodols on Mar 20, 2024 18:10:36 GMT -5
Have this amp which has kind of a weird issue.
The amps left channel is distorted at a certain level, while right is all ok.
What I have done so far.
Have checked the output transistors in-circuit and nothing is shorted .
Checked emitter resistors and nothing is shorted.
Swapped left channel driver board to the right channel as they are exactly identical down to the last component and connection. Distortion is none existent. So I’m thinking the board is good.
Swapped the Power Supply capacitors, the are 4 large ones 2 for each channel. Distortion is still there.
Each has it’s own power transformer and each own bridged configured diodes.
So changed the diodes with a bridge rectifier (the left -faulty) channel. Distortion is still there.
The amp has this led output volume indicator and circuit goes there to light up the LEDs as to which volume or wattage it is now. I removed that circuit board just to eliminate the board from possible suspects. And rightly so, distortion is still there with the board removed.
I also swapped the entire driver board and output transistors of the left channel to the right. So left channel now is using the right’s power transformer and right’s power supply capacitors, bridged diodes wires and all.
And there is no distortion when it’s there.
At this point I only have the power transformer as suspect that’s causing the distortion. Could it be the transformer?
There is this daughter board that’s kind of a late addition, but I have scoped it and distortion occurs prior to this board.
If you scope the left driver board when installed on the left power supply, distortion is detected of course.
But I have swapped it and the power transistors to the right, sound on the right is all Okay. Power transistors are mounted on the heat sink by the way, and it is kind of modular so one can just desolder and resolder to the other channel.
So it couldn’t be the board and the output transistors because of this.
I can’t, by the way swap the tight to the left as wires are not long enough. But when I get home maybe will do it.
The amps left channel is distorted at a certain level, while right is all ok.
What I have done so far.
Have checked the output transistors in-circuit and nothing is shorted .
Checked emitter resistors and nothing is shorted.
Swapped left channel driver board to the right channel as they are exactly identical down to the last component and connection. Distortion is none existent. So I’m thinking the board is good.
Swapped the Power Supply capacitors, the are 4 large ones 2 for each channel. Distortion is still there.
Each has it’s own power transformer and each own bridged configured diodes.
So changed the diodes with a bridge rectifier (the left -faulty) channel. Distortion is still there.
The amp has this led output volume indicator and circuit goes there to light up the LEDs as to which volume or wattage it is now. I removed that circuit board just to eliminate the board from possible suspects. And rightly so, distortion is still there with the board removed.
I also swapped the entire driver board and output transistors of the left channel to the right. So left channel now is using the right’s power transformer and right’s power supply capacitors, bridged diodes wires and all.
And there is no distortion when it’s there.
At this point I only have the power transformer as suspect that’s causing the distortion. Could it be the transformer?
There is this daughter board that’s kind of a late addition, but I have scoped it and distortion occurs prior to this board.
If you scope the left driver board when installed on the left power supply, distortion is detected of course.
But I have swapped it and the power transistors to the right, sound on the right is all Okay. Power transistors are mounted on the heat sink by the way, and it is kind of modular so one can just desolder and resolder to the other channel.
So it couldn’t be the board and the output transistors because of this.
I can’t, by the way swap the tight to the left as wires are not long enough. But when I get home maybe will do it.
