Swap your computer power supply with communcations supply to test. There is 12 v + & - with no test points that is also used to log into unit. If you can log in, run a "B" test for faults. Possible bad Bam Board. Its function is an interface and level converter for I/O to Computer. Also has any boards been replaced. New boards will come with the wrong bipolar proms for the job. Compare Proms with another car for correct versions for your software, Also bad memory board will do that. It is a 900 and not a 9000? 900 is an 8088 processor and 9000 & 900+ is a 286 with ribbon cable from cpu to mem board,
