Hi, I have been getting my butt kicked by this Infinity SW12 powered sub plate amp for a few months and am reaching out for some help. When it was brought to me, it had no sound. I had good signal going into the power amp but nothing coming out. I replaced the output MOSFETS Q11, 13, 15 & 17. I also replaced the PWM driver chips U7 & U8 and the op amps on the power amp board U9 & U10. Now I have sound but there is a very high frequency that is on the output signal that is there most of the time but occasionally it goes off and I get clean signal. I poked and prodded around every component with my wood chopstick looking for a trouble spot but didn't find any. I resoldered a ton of connections and the issue is still there. I checked all caps for bulges, leakage and unsoldered a few and checked for value. All ok there. I moved to the power supply and replaced BR1, Q6, Q8 R76 and R78 due to hot spots noticed on the PC board. Still have the noise. I have posted a screen shot of the output signal with the noise. I have also included PDF attachments of the schematic. First picture is of the amp on but no signal applied. Nice and clean trace. Second picture is of the signal with the high frequency component. Third picture is the output after the signal has been removed. The high frequency is still there. Any suggestions would be super helpful. BTW, this amp has numerous surface mounted components so it's a pain in the neck to work on.
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