Vintage Synth Repair

I have a farfisa compact duo. Everything works great except the output volume is
extremely low and a little noisy. I don't have the f/ar power supply, a friend built me a
box. This box worked perfect for a couple of years, now the output is extremely low. I was
told the power box does not have both ac and dc power, but it switches between the two, i
hope that makes sense to an electronics person. I tried the organ with an original box and
it's the same thing. My custom box might have damaged something in the organ,
but it work great for a couple of years, i'm not sure what it could have damaged. An
organ guy in town said it might be zener diods??? I'm not sure. All the organ notes and
effects work, the output level compared to noise is not too good. I appreciate any help or 
advice. I'm near Seattle, if anyone knows any repair people.
Thanks,
Hunter