I've owned my Chroma Polaris for many years and repaired it many times. This time its different... When I start it up many LEDs light upon the front panel and that's it. Same patter of LEDs every time; no response to playing the keys or pressing any buttons. Not much of a surprise once I get down and dirty inside. The CPU is running, I've scoped address and data lines on the RAM and ROM chips. There is no signal at all on PCS3. I've checked this line for  continuity from the CPU IC to the various spots where it is used and the connection is good This line enables the transfer of data to/from the front panel. So that explains why the FP is not responding. Always at logic HI. This is a processor line.so I figured maybe the 80186 has died or become damaged. I tried a new CPU chip... same thing.

So now I'm like well what could it be?

I have three revs of EPROM firmware and tried all three... same thing. I have a nice O'scope and DVM and some good tools and lots of parts from that era. I have the owner's and service manuals. As I said I've repaired this guy before but this time around I'm not sure what the trouble is. Any Ideas  on what is going on or what I should check next?

Lou