shadow game started up with ground row short on rows 1-8. check j206 j207 no short to ground so changed the u20 chip on cpu fixed the ground row short errors but now j206 j207 row 1,2 and 5 not working. checked the cpu with logic probe (first time using one)no pulse at j206 j207 pins 1,2 and 5 then checked u20 chip pin 1,2 and 5 on the input side all read low and output side 1,2 and 5 high evrthing else is pulsing. where does the signal come from for the u20 input side? what should i check next? hard to find info on this board evrthing seems to be for wpc-89

thanks your pictures are awsome make it really easy to figure out what should be going on. got a u23 chip on order

couple wrong chips sent and a month or so later finaly got the right parts. had to cut a 28 pin socket down to a 24 and got the right u23 chip, evrthing bench tests fine. so it was u23. is there any thing i should double check before putting the cpu back in the machine. all switch rows have bin checked for continuity to ground and all are good witch was the orignal error

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