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

--- In korgpolyex@yahoogroups.com, Marcus Wilson <JB@...> wrote:
>
> when you turn it on do you get a readout on the 7 segment displays?
> 
> 11 P
> 
> are you able to check that it sends and receives midi?
> 
> have you made sure that you have loaded in patches to ensure that  
> there is actually a waveform for the tg to create?
> 
> have you checked for output at the headphones AND the L-R outputs?
> 
> I had a poly that for a long time I thought was a dead TG, but ended  
> up being a dead headphone op amp
> 

Hi,

I've only just managed to find time to have another go with this
synth. I've loaded the factory settings, but the problem is still
there. The synth behaves perfectly in all respects except sound
output.

What I have found is that when a key is pressed, one of the
envelope inputs to the TG follows an ADSR curve as expected (so
the envelope DAC and S/Hs are working. As the envelope waveform
tracks out the curve, there is a small square wave on the footage
outputs whose amplitude also tracks the envelope as expected.

But, this square wave amplitude rises to, at most, about 0.2Vpk-pk
sat on a DC level of almost +5V. I would have expected these outputs
to be almost rail-to-rail (+-5V). There are other outputs from the
TG, 2 constant footage outputs (pins 1 and 2 IIRC) and a pseudo
random noise output. These outputs are working correctly (I think
they aren't used for anything in the Poly 800).

Cheers

mark-r