Solution:

Kindly using program DEBUG of MS-DOS, and assume the I/O address is 220H, disable all 6 channels IRQ. Then use PCL-10150-1.2 (50-pin flat cable) to connect CN0 and CN1. Then follow below description to see if the PCL-722 was a good one. Be sure RESET the computer first then follow below test. ================================================================================================= DEBUG -I 220 FF <== INPUT -I 221 FF <== INPUT -I 222 FF <== INPUT -I 224 FF <== INPUT -I 225 FF <== INPUT -I 226 FF <== INPUT. So -O 223, 80 <== set Port A, Port B and Port C of CN0 as OUTPUT -O 222, 55 <== OUTPUT 55 to Port C of CN0 -I 226 55 <== The INPUT Port C of CN1 is the same as Port C of CN0 -O 222, F6 <== OUTPUT F6 to Port C of CN0 (PC0 and PC3 as 0, rest bits as 1) -I 226 F6 <== The INPUT Port C of CN1 is the same as Port C of CN0 -O 222, 09 <== OUTPUT F6 to Port C of CN0 (PC0 and PC3 as 1, rest bits as 0) -I 226 09 <== The INPUT Port C of CN1 is the same as Port C of CN0 ================================================================================================= So far, if your test result is the same as mine, then the PCL-722 should be a good one. Otherwise, kindly return it for repair.