Vintage Synth Repair

Hi

I own a Siel DK-600 and its kinda under the weather.

I bought a copy of the schematics from Ebay.

I've tried a couple of things to try and fix it, but I still can't 
figure it out!

It comes on, it can change programs, it even sends midi!

But it doesn't make any sound and on the front panel both lights are 
stuck lit on the oscillators. A few of the other lights are stuck 
lit, but some of the lights seem to work fine like the octave lights.

Anyhelp would be appreciated its driving me crazy!

Thanks,

Tim