Hi,
I am chasing in issue with my beloved XM-7547. The amp worked fine in the car for quite some time but all of a sudden it started to distort. First I thought the mid range speaker went south but during my tests I connected a different amp and the distortion immediately disappeared.
I am a novice regarding amp repair so please be patient with me if I come back with "strange" questions or other weird thoughts 🙂
I finally did some first measurement with my new (and first) scope and I would like share to these with you.
My findings so far:
A. The power supply seems to work fine, railvoltage is present and stable (see screenshot)
B. There seems to be some "buzz" on the audio signal in the amp section (see screenshot). This is not the case when doing the same measurement with another Sony amp I have that is working fine.
C. When I connect a 4 Ohm load to the output of channel A the output signal (a 1kHz testtone) does not look like a perfect sinewave anymore (despite the buzz). With no load connected, this issue is not present (see both screenshots for comparison).
I have inspected the board for obvious signs of deterioration or burns but could not find anything. The only thing which I noticed (but that might be normal) is that the power supply pre-stage on the amp board (see picture) is pretty warm even with no load connected.
It would be great if you can guide me to further pinpoint the root cause. I hope the amp can be repaired so that I can use it again in the future.
Thanks a lot!
Holger
I am chasing in issue with my beloved XM-7547. The amp worked fine in the car for quite some time but all of a sudden it started to distort. First I thought the mid range speaker went south but during my tests I connected a different amp and the distortion immediately disappeared.
I am a novice regarding amp repair so please be patient with me if I come back with "strange" questions or other weird thoughts 🙂
I finally did some first measurement with my new (and first) scope and I would like share to these with you.
My findings so far:
A. The power supply seems to work fine, railvoltage is present and stable (see screenshot)
B. There seems to be some "buzz" on the audio signal in the amp section (see screenshot). This is not the case when doing the same measurement with another Sony amp I have that is working fine.
C. When I connect a 4 Ohm load to the output of channel A the output signal (a 1kHz testtone) does not look like a perfect sinewave anymore (despite the buzz). With no load connected, this issue is not present (see both screenshots for comparison).
I have inspected the board for obvious signs of deterioration or burns but could not find anything. The only thing which I noticed (but that might be normal) is that the power supply pre-stage on the amp board (see picture) is pretty warm even with no load connected.
It would be great if you can guide me to further pinpoint the root cause. I hope the amp can be repaired so that I can use it again in the future.
Thanks a lot!
Holger
