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Mac 512k Checkered Pattern

Posted by: Leonardo on 2021-01-17 16:21:16 Hello everyone. I have a Mac 512K that just displays that checkered pattern at boot. I already replaced the ROMs with those of a working Plus. In fact, even without any ROM, the pattern is the same. The continuity of all ROM pins is fine and voltages are ok, too (recaped analog board). I was also poking with the oscilloscope and found that pin 8 of VIA (PA6 - vid.pg2) has no signal. Can it be a problem with VIA or it shouldn't interfere with the boot? I appreciate any help. Thanks.

Posted by: Leonardo on 2021-11-25 17:21:36 Hi guys. A quick update after a long time. I found the problem really was with the VIA (6522). It is essential in the Mac startup process. I replaced this chip and now have a working Mac 512 again. So if you're seeing a similar pattern on your Mac 128/512, be wary of ROMs first and then 6522.

Posted by: cheesestraws on 2021-11-26 02:05:16 Thankyou for the information on this!

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