Check all of the address and data lines for continuity from the 80C85 and the outputs of IC 23 and IC29.
Check for low signals on the outputs of IC29. If you don't see any brief lows except for Y0, Y1 and Y2 then there's a reasonable chance that the software memory check is stopping the CPU from progressing anywhere.
If you see lows on Y3-Y7 then the RAM check is probably coming up OK and you'll have to look further.
An oscilloscope is immensely useful.
/Mike
From: "mmdatech@... [korgpolyex]" <korgpolyex@yahoogroups.com>
To: korgpolyex@yahoogroups.com
Sent: Saturday, November 28, 2015 3:52 AM
Subject: Re: [korgpolyex] another dead 800
To: korgpolyex@yahoogroups.com
Sent: Saturday, November 28, 2015 3:52 AM
Subject: Re: [korgpolyex] another dead 800
Thanks for the reply,
I've already checked the 8085 clock out ( 3Mhz ) and Res7.5 signal ( 3000hz )
and replaced the eeprom testing both firmwares posted in the files section.
Still no go...
However, another clue is the lack of signals at the A,B,C ports of the 8155 IC
while still getting the desired Timer out ( 500Khz ) signal when the eeprom is installed.
What is the best strategy for testing the DTC's and the 6116 ?