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@dalek,
If your comments were directed at me, then I think you are misunderstanding slightly what I'm saying.
I'm using the fact that the _WE pin 21 on the Agnus chip is not connecting to pin 21 on the socket to measure whether it is Agnus that is driving/holding /WE high, or if it is something else is.
With the _WE pin 21 on the Agnus chip isolated from pin 21 on the Agnus socket, it is still measuring high - so it seems that it is Agnus that is driving it high.
Even when I do use a piece of solid wire to bridge the gap between Agnus chip pin 21 and Agnus socket pin 21 and continuity is good to pin 17 on U35, the _WE signal is still driven high (by Agnus, as found in the test above).
The Agnus chip has been tested in a working A500+ and that boots up to the Kickstart screen OK. All the other chips have also been tested in the working A500+ board, along with U10/U11/U12/U13 and U34/U35 chips. I've check all the pins/traces for the Agnus pins and they all seem OK.
But I think _WE being held/driven high is more of a symptom rather than the cause of why this A500+ board cannot boot. I just don't know what else is wrong that is causing _WE to be driven/held high. I'll probably end up checking all memory related traces yet again, as I can't find anything else yet that is giving me a clue as to what the problem is.
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