Apple Lisa minimal card setup

[robin-fo]

Hi everyone, especially our Lisa experts here!

@AlexTheCat123 @warmech @RolandJuno

I'll hopefully soon test the Lisa Replica PCBs I've been assembling for a year or so now...

I have the following question: A Lisa can boot with the Motherboard and CPU card only – right? It will report an error obviously, but you'll have something on the screen at least. How is this possible if the soft power is controlled by the IO card? Do I simply have to switch on the PSU manually? I'm using the Lisa Breakout PCB for now. https://github.com/RolandJuno/Lisa_Breakout

Many thanks in advance,
Robin

 

[stepleton]

What am I, chopped liver? Sheesh.

I'll show you --- I'm going to march right upstairs, pull the card cage out of the 2/10 and yank out all but the CPU card and report back.

 

[stepleton]

The results are as follows:

With only a CPU board, the Lisa turns on immediately after power is applied, and the screen shows garbage:

(note: flashing images on the screen) https://photos.app.goo.gl/ss45GQ9gsFnigvCMA

With a CPU board and RAM populated, the Lisa still turns on immediately, showing an Error 41 on the CPU board as it continually redraws the screen. Retrace lines are visible.

(note: flashing images on the screen) https://photos.app.goo.gl/kgRQf9f5p2aYeNge6

YOU'RE WELCOME

 

[robin-fo]

What am I, chopped liver? Sheesh.

Sorry I forgot to mention you in the list of Lisa experts

Many thanks for checking, this is very kind of you!

So I need a working RAM card as well… I have two genuine ones in unknown condition, but with some signs of corrosion. I‘ll have to try them.

Composite output will work in that condition I guess?

 

[stepleton]

So I need a working RAM card as well…

It depends: even though the garbage isn't much to look at, it's still informative. The screen image is still a raster, so if you see it, that means the video state ROM and other video gubbins are working at least, and that ain't nothing! Here's where you really do want to hear from folks like the ones you've tagged: I'm not sure to what extent that screen means the CPU is executing code. They may know.

Composite output should work to show you the screen junk.

Good luck with your build!

 

[robin-fo]

The screen image is still a raster, so if you see it, that means the video state ROM and other video gubbins are working at least, and that ain't nothing!

Excellent!

 

[robin-fo]

I get nice waveforms out of the Video / Sync / Composite signals. However, I don't have my old B/W TV at hand currently.. I have a Samsung Smart TV, but it doesn't sync to the composite video output apparently. Is this to be expected? Could I convert the Video + HSYNC + VSYNC signals to VGA? Or would I have similar issues as with the IIgs RGB output and modern displays?