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Author Topic: Reproducing the Lisa 2 Card Stack: The CPU Card  (Read 604 times)

warmech

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Reproducing the Lisa 2 Card Stack: The CPU Card
« on: August 08, 2022, 03:19:05 pm »

So I recently mentioned that I was looking for a dead CPU card and, thanks to jamesdenton, that's about to be fulfilled (just waiting on the postman). James has generously allowed me to completely depopulate it and scan it for reference for this task, but I need to find someone/somewhere with a 1200dpi scanner that can handle this board.

Stupidly, I had forgotten to start a thread about my work on the RAM card, so that will get posted shortly; until then, some background. I've taken a step back from repairing my Lisa 2 to address another issue I'd run into - the lack of generally available replacement hardware. One of the problems I'm facing (arguably, the greatest) is my I/O board; while the motherboard escaped relatively unscathed, the I/O board is heavily damaged. As I removed components to asses damage, it became apparent that the corrosion was much more widespread and thorough than initially presumed. Frustrated, I started exploring the possibility of outright replacement of the I/O board and found that, while new replacements existed, they were generally unobtanium. Not that I wasn't interested in repairing my own, but the amount and extent of damage was very daunting. After taking a break from working on my Lisa, I played around with the idea of just recreating the card stack altogether: what if someone owned a Lisa chassis but no brain for it; what would it take for them to just... make one? Eventually, I got pointed in AlexTheCat123's direction by someone on TinkerDifferent and decided to reach out. As a result, I opted to chase after reproducing some of the card stack that Alex hadn't had a chance to look at yet, namely the RAM and CPU cards.

While work on the RAM card is basically 99% done (I'm taking my eyes off it for a couple weeks so I can come back with a fresh perspective to check for errors), work on the CPU card has been underway for about a week now. The schematics have been replicated and I'll be starting in on the board layout once I have the scans in hand; all said and done, this was about a weeks worth of work in my free time so I'm happy it went as fast as it did. I got this done in about the same time it took me to do the RAM card's schematics, so I'm going to interpret that as having at least advanced my skills a little bit, lol. I'm definitely not looking forward to laying down all the traces, as the number of them is substantially higher than the RAM card. It may be a couple of few weeks before this is ready, but I'm looking forward to it being done. I'm aiming for this to be as close to a 1:1 reproduction as I can manage, but I plan on making a couple of very minute "quality of life" improvements to this thing. Two of which are: a) adding traces for factory bodge wires that will be attached to jumpers and, b) moving the ceramic cap attached to the legs of U5C to dedicated pads nearby. Like I said, infinitesimal changes, but they'll help make the board just a little less cluttered.

Here's where I am at the moment - this should look better in a few days, lol...

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sigma7

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Re: Reproducing the Lisa 2 Card Stack: The CPU Card
« Reply #1 on: August 08, 2022, 04:59:36 pm »

It looks like you've got a lot done!

Couple of thoughts:
  • If you want maximum compatibility with the optional do-dads (XLerators, ROM Switcher), then the socketed parts (at least) probably should be in the same physical locations as the original.
  • It is likely there are some difficult to obtain components (or soon to be); you might want to check out availability and consider substitutes before finalizing the design.
  • You may or may not want to consider the 4MB modification https://lisalist2.com/index.php/topic,29.0.html (perhaps just with a spare DIP pattern or you could go further)

(I'll add to this list if I think of more)

edit: added 4MB mod
« Last Edit: August 08, 2022, 05:09:05 pm by sigma7 »
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warmech

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Re: Reproducing the Lisa 2 Card Stack: The CPU Card
« Reply #2 on: August 08, 2022, 05:51:57 pm »

It looks like you've got a lot done!

Couple of thoughts:
  • If you want maximum compatibility with the optional do-dads (XLerators, ROM Switcher), then the socketed parts (at least) probably should be in the same physical locations as the original.
  • It is likely there are some difficult to obtain components (or soon to be); you might want to check out availability and consider substitutes before finalizing the design.
  • You may or may not want to consider the 4MB modification https://lisalist2.com/index.php/topic,29.0.html (perhaps just with a spare DIP pattern or you could go further)

(I'll add to this list if I think of more)

edit: added 4MB mod

Thanks! I'm just glad I can quit staring at the schematics for a while, lol!

In regards to what you mentioned:
  • I'm aiming to have everything as close as possible to where it is on an OEM board; obviously, getting down to the hundredth of a millimeter is probably not going to happen, but I'd like it to be as close as is feasible.
  • 74XX-series logic should be okay for the next little while, but I'm definitely worried about the on-board RAM and video ROM. Thank you for bringing that to my attention; I'll get with my friend who's much more the wizard of that realm and get his advice.
  • I had considered the 4MB mod, but I wouldn't have a way to test it. It requires the square pixel mod, which in turn requires replacing the CRT neck connector, correct? If not, I can take a look at squezing in the required hardware.

Keep 'em coming - it's going to be a few days before I get the board layout started, and even then a week or two before I get far enough along that re-organizing things would be too much of a chore.

Also, initially, just the gerber files will be released for all of this. I need to teach myself how to use KiCad so I can provide raw hardware modifiability as an option for folks eventually. Once I get comfortable using it, I'll migrate the schematics for everything and redraw the boards. I know it's a lot of work and would probably be more efficient to do that now, but I mostly just want to get this stuff put to paper before I lose the will finish, lol.

EDIT: If anyone has a modded CRT neck connector for the pixel mod they wouldn't mind sending me, I'd love to try to reproduce that at some point as well.
« Last Edit: August 08, 2022, 05:53:52 pm by warmech »
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sigma7

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Re: Reproducing the Lisa 2 Card Stack: The CPU Card
« Reply #3 on: August 08, 2022, 07:14:01 pm »

I had considered the 4MB mod, but I wouldn't have a way to test it. It requires the square pixel mod, which in turn requires replacing the CRT neck connector, correct? If not, I can take a look at squezing in the required hardware.

The square pixel kit includes a transformer that goes inline between the video board and the horizontal winding of the yoke. (So installing it involves disconnecting a cable from the video board and connecting the transformer between that cable and the video board.)

In my experience, the square pixel ROMs do work reasonably well without the transformer -- you may not be able to adjust the horizontal width to fill the screen, so your image may be smaller than ideal, but it is clear/big enough to read.

I've got some notes somewhere about the composition of the transformer, I'll post those when I find them.
« Last Edit: August 08, 2022, 07:16:36 pm by sigma7 »
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warmech

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Re: Reproducing the Lisa 2 Card Stack: The CPU Card
« Reply #4 on: August 08, 2022, 07:17:02 pm »

Oh dang! I assumed it [ROMs] was dependent on hardware to function correctly; it didn't occur to me the neckboard/transformer was just to compensate for an aberrant screen width. I'll absolutely work on adding the 4MB mod, then.

EDIT: I responded too soon! That sounds excellent - I have a reasonable amount of experience working with CRTs, so if all it needs is a fairly simple transformer in-line with the deflection hardware, then that may be a longer term goal of mine to reproduce.
« Last Edit: August 08, 2022, 07:19:27 pm by warmech »
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sigma7

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Re: Reproducing the Lisa 2 Card Stack: The CPU Card
« Reply #5 on: August 10, 2022, 05:52:30 pm »

I've got some notes somewhere about the composition of the transformer, I'll post those when I find them.

Here: https://lisalist2.com/index.php/topic,311.0.html

When the 3A ROMs are used without the transformer, the left side of the image may be wrapped back on itself and the Horizontal Position control doesn't have enough range to fix it.

The regular video configuration works ok with the transformer installed, so once installed you probably won't need to remove it, but it is preferable to adjust the controls on the video board when switching between the video configurations.
« Last Edit: August 10, 2022, 06:02:50 pm by sigma7 »
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warmech

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Re: Reproducing the Lisa 2 Card Stack: The CPU Card
« Reply #6 on: August 10, 2022, 11:45:32 pm »

That's fantastic! Once I have my Lisa operational, this is getting bumped to the top of my list.
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compu_85

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Re: Reproducing the Lisa 2 Card Stack: The CPU Card
« Reply #7 on: August 13, 2022, 08:47:07 pm »

However, with the 3A ROMs you're limited to Macworks... you can't run the Lisa Office System, or Unix :(

-J
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