80186 multi buss system problem

Grant grant at millhouseindustries.com
Sun Dec 6 19:34:13 CST 2015


I’m looking for some help diagnosing a old Grid server problem,I am a hobbyist learning my way around old computer systems .
The system consists of three boards labeled
Diagnostic server
File server
Com server

Each board contains a 80186 , ram and rom and are all connected via a backplane.
The diagnostic server has rs232 port and a connector to a small led display.
The file server has a GPIB port and a something along the lines of a SASI port
The com server has what i believe to be several rs232/422’s ports at least

What i know works is the diagnostics server and the file server as i can interact with the diagnostic server via a serial terminal and the file server attempts to boot from a gpib floppy but i have no boot media that will boot it.
The problem is with the com server board, when the system initializes the diagnostic board does a self test then looks for other boards on the system it finds the file server board but does not find the com server board.
If i remove the the file and com server and power them out of system, reset the processor’s and then probe the different signals they appear to be operating the same,clk activity , data and address buss activity is identical. When i put them in the system and watch the file and com server boot it looks like the com server get stuck when it goes to send its data to the diagnostic server.  I'm just a amateur at these things, i am looking for help to point me in the right direction. i made a small video of a typical data line at boot the first is the file server then the com server where you can see it get stuck , this is typical of all the signals that i test.

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