Edit: screen picture is not attached, here's a link: https://photos.app.goo.gl/zy6vBiuoYziDXa6J3 Hi all, I'm not progressing much on this 2001. I'm now able to test the 6550s out of the PET and I've found two surely bad (also confirmed using them as video RAMs). Most of the times it just boots directly to an illegal quantity error, but sometimes displays the basic prompt without the bytes free amount as you see in this picture. I've suspected a problem reading the video ram (writing just works, otherwise it wouldn't clear the screen and display correct characters), but running the system with a nop generator showed no obvious problem on the bus transceivers or address decoders and anything else I could test. Screen scrolling looks a bit too "jumpy" compared to what I'm used to see on 3032, but I really don't see any problem in the video ram to data bus glue circuits. I'm still not able to test the ROMs either inside or outside the PET (working on both ways), but would any of you believe a ROM to be so marginal to work sometimes? I've tested continuity on the sockets, displaying running addresses and ckecking data path continuity to the CPU's data pins. I'm waiting for PCBs to use 2716 EPROMs in place of the 6540s (designed one myself, rather than copying someone elses one) and started adding support for the 6540s to my multiple-odd-memory-tester, but in the meantime, any other thing I could check? Best regards Frank Message was sent through the cbm-hackers mailing listReceived on 2018-01-06 18:00:03
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