osiweb.org

I am really enjoying watching the progress of your restoration of this machine.

Dave

Hi Philip, If your B&W board is a 540B, then it can do color. As long as the only thing missing is the crystal, and you already have the extra 1K RAM and supporting circuitry (I think an 8T26 and a couple of latches) installed, and some additional color generation circuitry installed, you should hav...

That's great about the power supply. The disk sounds painful. It looks like you are destined to have a look inside. . .

Nice progress! I think the LM723 is a pretty common part; should be easy to find. Good for you for looking up the part cross reference. I started a list of part numbers for replacements for various OSI parts, but it's pretty short at the moment. I will add this one to the list, since I suspect that ...

Fantastic! Seems like you had this one in the bag without any help. As for the power supply-- To my knowledge, OSI bought all of those, and I am not sure if they always used the same vendors or models. I don't ever recall seeing the schematics in the manuals. Can you post some pictures of the bad po...

I'm getting more suspicious of U5E. Are the chips socketed?

Actually, I started with your schematic, and just re-arranged everything, then started swapping some stuff out. I have seen lots of multi-turn trimmers with the inline configuration, so I didn't really think much of it. I just checked the Mouser catalong, and there are several pots that will fit as-...

]The picture is very helpful. I'll include it below: IMG_2836.jpg First a disclaimer. I used to be intimately familiar with the workings of the 540A board, but that was in 1978 - 1980 or so, so I'm trying to remember, and look through the circuit, which is a bit complex; so I may be making some mist...

By grounding the select line of the 74157, you are selecting 32 column mode. This selects the 6 MHz dot clock (12 MHz divided by 2 by the 7492) instead of a 12 MHz dot clock, and resets the column count after 32 characters instead of 64. The three chips, U5C, G, and E are counting characters across ...

I thought I had got the overlaps out, but may have moved something. I will make sure it's clean before sending it off. Those overlaps are due to a couple of "net ties" I placed. Instead of tying unused gate inputs directly to ground, I insert a "net tie", which is like a zero ohm resistor made out ...