Korg Poly800/EX800 Users

Hi all,

I'm trying to get an MK1 Poly 800 back to life. I suspect that the tone 
generator chip (IC3) is faulty.

The clocks to pins 19 and 20 look OK, and the envelope inputs E0-E7 
rise and fall as expected when I press keys. The power supply pins look 
OK too, and the data, address, ALE and ~WR are all clocking nicely. 
However, there's nothing much on the footage outputs. They're all more 
or less stuck at +5V, although there's a little square wave wobble on 
some of them whose amplitude tracks the envelope input.

Is it likely that my TG is busted, or am I missing something else?

Cheers

mark-r