Korg Poly800/EX800 Users

It may well be something else that is stopping the display from
operating. Such as for example, the CPU bus lines, decoders, latched
and supporting DTC's etc need to all be working for anything at all to
happen.
Have you checked the troubleshooting procedures and gone through them?
And the main circuit descriptions?
You could start by checking the CPU RES_7.5 interrupt line. If the
clock going into that isn't working, you won't get any display either.
One thing worth testing. Does pressing a note cause ANY change in the
audio output? Does pressing a note result in a MIDI note on output?
/MikeOn Sun, 2019-03-10 at 03:15 +0000, studio_1a@... [korgpolyex]
wrote:
> Hi everyone, so after replacing many parts and qualifying all voltage
> rails on the KLM596 board, I fired it up and the display is not
> turning on. I swapped the original KLM596 board with a spare and the
> display comes on, so I know the connector/harness and display board
> are good. I checked all timing signals / address lines from the CPU
> to the 81c55 with my scope and they are present on the 81c55 but
> there is no output on PC and PB ports or T/O, so i suspect its b/o
> unless something is loading it down? any suggestions? all traces and
> lines were qualified between IC24-IC25-IC30-IC31.
> The IC is marked as MSM81c55RS, do I need an exact replacement or
> will any other variations do?
> 
> 
> thank you
> 
>