Korg Poly800/EX800 Users

I don't think you could measure the RES 5.5 and 6.5 with a DVM very 
well since it's such a low duty cycle pulse. You're seeing 1.45v on 
the RES 7.5 line which is probably normal. I would try to beg or 
borrow a scope to go much farther than you did. You actually did 
really well for using only a DVM. 
Other clues would be: Are any of the chips getting warm. Most 8080 
type processors when they fail get quite warm to the touch. Many 
times I have shotgunned CPU's (even though I do have a lot of test 
gear and a good scope) just because they were a lot warmer than any 
other chip on the board. I'm not sure if the CPU has to run to 
produce a sound you can vary with the filter section pots. The noise 
generator may be able to run without any outside influence. I do know 
the CPU controls the envelopes. 
The 81C55 memory chip may be a good place to start too since these 
fail quite often if a spike or any ESD hit the board.

Let us know what you find, Fran
--- In korgpolyex@yahoogroups.com, "selloutdesigns" <aah_public@...> 
wrote:
>
> Stop me if you've heard this one before...Bought an "As Is" Poly on
> eBay. Cleaned it up, plugged it in a lo and behold no display. Sound
> is present at the headphone jack about 30 seconds after turning on.
> It's a frequency sweep from low to high (sounds almost like the 
whoosh
> of a jet engine starting) followed by constant white noise. This 
sound
> is affected by turning VR1, VR2 and VR3 trimpots.
> 
> I'm okay at basic electronic troubleshooting and repair, but have 
run
> out of ideas, so wondering if anyone has had a similar experience. I
> have pretty much determined it is not a power supply circuit issue 
(as
> I was hoping when I bought it). All the IC's I sampled are getting
> correct power. Also on connector KLM596 CN6A, Pin 6 shows 4.98v, 
Pin 8
> shows -5.07v and Pin 9 shows 9.44v, all of which I believe to be
> normal and show the power section is working OK.
> 
> Unfortunately, I do not have access to a scope. Is it even worth 
going
> any further at this point without one? In a previous post where
> someone had a similar issue, it was mentioned that if the RES6.5 
clock
> was not running this could cause a dead display. I did check RES
> 5.5,6.5 and 7.5 pins on M80C85A chip. RES7.5 pin shows 1.45v, but 
the
> other two are 0v or at least < 1 mv.
> 
> Any ideas or suggestions on where to look next?
>