I've purchased a pair of EQ573 modules and one is making an awful noise whether or not the EQ is engaged. I've included a snip of a frequency analyzer with white noise running through the modules with the HP filter engaged at 360 Hz. You will notice that the bad module is about 30 dB louder than the working module, and there is a substantial noise floor even below the HP cutoff freq. This makes me think there's an issue with the gain stages after the filters.
While I'm waiting on a 500-series extender for voltage probing, I'm going to reflow the solder joint on the IO board which look suspect. While I'm poking around, does anyone have any other ideas to narrow down the issue?
According to the original owner, this unit allegedly worked perfectly fine at one point, but started to go bad over the last year or so.
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