BijanK
New Member
I guess I need some help with this.
I have a YAMAHA AX-870 on the bench whose right channel was significantly quieter than the left. I have traced the fault back to a defective right-channel op-amp on the volume control board (NJM2068SD). As the component is rare, a Chinese import was the only option. However, it came from a reputable dealer and looks perfectly alright (both brand-name JRC). After the replacement, the sound is now flawless on both sides; the sound quality is superb.
But: when switching off the device using the power button on the front, there is now a loud ‘popping’ sound—so loud that I was worried about my speakers (but only on the left channel). In addition, the ‘Pure Direct’ switch (bypassing tone control) could no longer be used: after pressing it, the protection circuit was activated and the relay clicked repeatedly.
I considered some faulty soldering or missing ground and reflowed the left-channel op-amp. Result: problems still there and now the left channel is completely gone. Huh?!
I then replaced the left-channel op-amp again with a third chip. Now the sound is great again on both channels. ‘Pure Direct’ is available again with no relay action. The 'popping' on shut-down is still there, but much less pronounced.
What am I seeing here? A defective part? A fake part, maybe?
I have a YAMAHA AX-870 on the bench whose right channel was significantly quieter than the left. I have traced the fault back to a defective right-channel op-amp on the volume control board (NJM2068SD). As the component is rare, a Chinese import was the only option. However, it came from a reputable dealer and looks perfectly alright (both brand-name JRC). After the replacement, the sound is now flawless on both sides; the sound quality is superb.
But: when switching off the device using the power button on the front, there is now a loud ‘popping’ sound—so loud that I was worried about my speakers (but only on the left channel). In addition, the ‘Pure Direct’ switch (bypassing tone control) could no longer be used: after pressing it, the protection circuit was activated and the relay clicked repeatedly.
I considered some faulty soldering or missing ground and reflowed the left-channel op-amp. Result: problems still there and now the left channel is completely gone. Huh?!
I then replaced the left-channel op-amp again with a third chip. Now the sound is great again on both channels. ‘Pure Direct’ is available again with no relay action. The 'popping' on shut-down is still there, but much less pronounced.
What am I seeing here? A defective part? A fake part, maybe?
