KLund1 Posted February 12, 2018 Share Posted February 12, 2018 Found this in an 800 OS card. Any idea what it is for? Quote Link to comment Share on other sites More sharing options...
Bryan Posted February 12, 2018 Share Posted February 12, 2018 It appears to drive Pin 20, which looks unused in the schematic. I'm guessing it's an address decoder for some other device. Quote Link to comment Share on other sites More sharing options...
1050 Posted February 12, 2018 Share Posted February 12, 2018 One of it's inputs is 0xD7xx region which was used for the Byrd ram upgrade. The extra chips are where this one doesn't fit the Byrd though, the Byrd just tapped pin #7 from from the 138 and took it to slot 20 and that's all that was done to the OS board. They could be refining the address down to 0xD7Fx or further? Similar thread here http://atariage.com/forums/topic/272453-requesting-help-identifying-an-atari-800-ram-upgrade/ Quote Link to comment Share on other sites More sharing options...
KLund1 Posted February 12, 2018 Author Share Posted February 12, 2018 Two others things about this 800. There is ribbon cable running from the inside pins of the SIO port to another sio port cut out of the rear of the case. And there is a LED in the front of the case just in front of the space bar. It goes to CR210 and CR202 on the power PCB, the contacts closet to the front of the case. There are no modifications to any of the ram cards. I have not pulled it completely apart to see the CPU or motherboard yet. Quote Link to comment Share on other sites More sharing options...
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