You have something wrong in your switch test results, can't have 1J8 (Strobe) Pin 1 to 1J10 (Return) Pin 2 giving both "7" and "16" as the results. I suspect you mean that you have 1J10 Pin 1 jumpers to 1J8 Pin 1 = "8", then move jumper to 1J8 Pin 2 = ""16", then move jumper to 1J8 Pin 3 = "24" and so on.
Basically you are first checking that all the returns (0-7) are functioning by using a single strobe and connecting it to each of the 8 returns (0-7) one-at-a-time, then you are checking each strobe by connecting one return to each strobe line, again, one-at-a-time.
Based on that assumption, you have damaged gates on IC52 and IC51 (use the diode check for those: http://www.flippers.com/service.html#diode ). Note that the 6821 PIA U15 gates that are connected to IC 51 & 52 may be damaged, however this too can be checked with the Diode Test once IC 52 and IC 51 are removed. It could well be fine.
Your strobes all check out fine by the way.
Don't replace ICs unless you are certain they are damaged, it is possible to do more damage to the board as you are unlikely to have the desoldering skills or tools of professional board repair folks...clip the legs off at the IC, unsolder them and clean out the holes prior to inserting a double wipe or machined pin IC socket. Do not use cheap IC sockets, they will always cost you in the end (or sooner).
John :-#)#
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