Yamaha EMX-3000 powered mixer with issues

Hi guys.

I just received a Yamaha EMX-3000 powered mixer for servicing.
This mixer had its power transformer changed from 240VAC to 120VAC. It is kind of a crappy conversion: the original toroidal transformer was replaced with a square one that is a little bit to big for this mixer. So someone made it fit, cutting out a square piece of the metal shielding between the console and the amp section, right above the trafo and squeezed it inside the enclose.

Issue #1: The mixer has developed a strange noise. With all faders down (no volume), a tone starts at about 1000hz and gradually moves down to about 100hz, then goes away and after about 5 seconds starts over. This goes on and on.

Issue #2: The digital effects built into the unit is not working.

Issue #3: 2 input channels out of 8 have more gain than the others. Im not yet sure if these two are overdriven or the other 6 channels are "underdriven"...

Any idea how to approach these issues?

Thanks in advance!
 
sounds like a hot mess with the mods to accommodate a replacement transformer...

with the effects not working and the sweeping noise you mentioned i would unplug CN101 and CN102 from that pcb to see if that removes your noise. simple to do to start sorting things out.
there's no switchable pads on the EMX so that doesn't help with the gain differences...which channels i particular?
 
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the thing that usually kills the FX module is severe feedback(from an open mic)...as i don't have a hot air rework station i don't even attempt things like replacing the MCU and ZFX chips and replace the entire board. not cheap, i know...but you can still route to external outboard FX that are much better.
i hope tracing down the gain differences will be easier!