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American Microsemiconductor has 8T26's and 8T28's in stock for a reaonable price. If you get a bunch of one chip or the other, there are some places you can replace 8T28's with 8T26's and vice versa. For example, you can replace all the bus drivers in a C2/4/8 system with the same type, either th '...

Giving a second thought to the video, I'm not sure a 6545 controller chip would be able to switch between 64 and 32 columns with a single line from the latch at $DE00. Any recommendations for a PIC? I did a web search and all the PIC-based video solutions seemed to only handle very low resolution......

Another quick note: I looked through the OSI board archive and discovered that the 24K RAM board I have is identical to OSI's 527 board, however of course missing the OSI labelling and copyright.... some IC's and switches are also missing from my board.

Steve

Followup... When I substiture my original C4P cpu board into the machine it boots normally. 24K board is removed. So it appears to definately be a problem with the new cpu board. I might try some simple chip swapping.... 2114's, 8T26's. As an aside, the components near the J3 connector differ signif...

While repairing my new C4P I thought I'd pull out my Superboard, which also was not working. I thought I'd make a new post to keep things separate. Anyway, I'm not sure how I overlooked this before but the machine is missing the two 2T28 chips beside the CPU (UC6 and 7 if memory is correct). I under...

Cool. I'd start by removing the mod, and the RAM board, and powering up with just the video and CPU cards, positioning the CPU on top so you can access it with a probe. What kind of test equipment do you have? Dave Good ideas. I only have a meter and logic probe (that I havent used in many years). ...

A followup... the report was correct. The machine boots to the normal "garbage" screen but won't reset. I pulled out my original C4P (floppy system) and now it's doing the same thing. So now I have two machines to repair... My machine was working a few years ago when I last tested it, so it shouldn'...

Hi, I just picked up another C4P machine yesterday... not working. I'm hoping to fix it up. It has the standard basic in rom, cassette operation, the 502 cpu board and 540-Rev B1 video. It has a 24K ram card that has no model number, however on the underside there is what I believe is a logo, which ...

Hi All, Not too much activity lately, so I thought I'd post about something I've had in the back of my mind for a while. Has anyone thought about recreating an OSI machine from "newer" parts? Not new like FPGA, but new as in individual components. You could replace all the original 2114 ram chips wi...

Hi, Sorry, it appears I measured wrong or made a typo for the back dimension and top-front... The rounded corners probably messed me up. The numbers I gave are the INSIDE measurements. Back: looks like 92mm inside (96mm outside, which I guess makes the thickness of the case about 2mm). Top-Front (fa...