Analog board (video) testing without logic board

[speakers]

I'm restoring an SE/30. The logic board needs recapping but the analog board and PSU are in pristine condition.

So while I'm working on the logic board, is there a way of testing the video generation without the logic board being connected? Can the video signals be fudged to display a blank white screen?

 

[luminescentsimian]

In theory, yes, if you can get your hands on a Raspberry Pi Pico or other RP2040-based board running CircuitPython. I made a script and PIO program to generate a classic mac 512x342 signal to use to test another program that converts that signal to 1024x768 VGA. Going by this diagram, https://retrocomputing.stackexchang...-the-mac-se-30-send-video-to-the-analog-board , as long as pins 9,10,11 aren't pulled up to 5V you should be able to bodge them to pins 16, 14, and 15 of the Pico to get a test pattern. Also a ground line connected between them.

macvid/generator-py/code.py at main · crackmonkey/macvid

Mac classic video capture and translation on an RP2040 - crackmonkey/macvid

github.com

I haven't gotten my hands on a real classic Mac to test this or verify that the timings are 100% accurate but I think it'll get you something.

 

[speakers]

In theory, yes, if you can get your hands on a Raspberry Pi Pico or other RP2040-based board running CircuitPython. I made a script and PIO program to generate a classic mac 512x342 signal to use to test another program that converts that signal to 1024x768 VGA. Going by this diagram, https://retrocomputing.stackexchang...-the-mac-se-30-send-video-to-the-analog-board , as long as pins 9,10,11 aren't pulled up to 5V you should be able to bodge them to pins 16, 14, and 15 of the Pico to get a test pattern. Also a ground line connected between them.

macvid/generator-py/code.py at main · crackmonkey/macvid

Mac classic video capture and translation on an RP2040 - crackmonkey/macvid

github.com

I haven't gotten my hands on a real classic Mac to test this or verify that the timings are 100% accurate but I think it'll get you something.

Sadly, I don't have a Pi and should .. because this is yet another case where a Pi's handy .

I also came across https://trmm.net/Mac-SE_video/ using the same technique.

 

[luminescentsimian]

Nice. Looks like they used the BeagleBone's PRU which is similar but more capable than the Pico's PIOs. Pi Pico's are about the only Pi's you can regularly get your hands on right now, I have two on a USPS truck out for delivery today.