68kMLA Classic Interface
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| MacPicoVid output from Macintosh Plus | |
| Posted by: bigmessowires on 2026-09-26 14:00:54 I've been working towards a desktop setup for running bare Plus and SE logic boards, without the analog board, CRT, or anything else from the original Mac case. I've built an adapter cable for a standard PC ATX power supply, and it's working. For the video output I picked up a MacPicoVid, which is a productized version of guruthree's Mac SE Video Converter: https://github.com/guruthree/mac-se-video-converter It uses an RP2040 to sample the CRT video signal and create a standard 640x480 VGA signal from it.  The video output works - sort of. As you can maybe see in this very poor photo, the disk icon with question mark shows up, but the gray checkerboard desktop just isn't there. I can't imagine what would cause a big like that, any ideas? Guruthree doesn't mention any issue like this in the list of common troubleshooting issues. My cable connections to the MacPicoVid are temporary and iffy, so maybe this is just a signal quality problem that will disappear when I have a better cable solution. Could this be a flaw with the Mac itself? It's curious that a few pixels of desktop are visible just at the rounded corners of the disk icon. For what it's worth, the monitor that I'm testing with is a Dell that's been used successfully with many other classic Macs, although maybe something particular about the MacPicoVid output is causing it grief. | |
| Posted by: Nixontheknight on 2026-09-26 16:36:17 that's something that's covered in the dead mac scrolls | |
| Posted by: bigmessowires on 2026-09-26 17:15:05 The missing desktop pattern was a problem with the Mac itself! I wouldn't have guessed that. The problem persisted after building my final cable harness, so I tried a different logic board and the desktop immediately appeared. If it matters, the no-desktop Mac was a Plus and the second Mac was a 512K. Here's the Mac 512K desktop displayed on my Dell LCD.  Windows, icons, and menus look good, but the desktop pattern appears somewhat noisy and staticky. You can't really capture how it looks in a photo. I was able to mitigate the effect somewhat by playing with my monitor's phase setting, but I couldn't find any setting that really looked solid. Maybe I'm too picky. It's definitely usable but it's still a little disappointing. The original Github project's troubleshooting suggestions say that for flickering or noisy pixels, you should adjust the number of nop instructions at a critical spot in the code. I'll try that at some point, although the photo of the kind of noise you can expect with the wrong number of nops looks quite different from what I'm seeing. The issue is more likely my monitor or my cable job. It would be interesting to see how the image from a digital video output like MacDVI looks in comparison: https://68kmla.org/bb/threads/macdvi-oss-pico-2-based-ttl-to-dvi-video-converter.52268/ Speaking of cable jobs... oof. I started out with an ATX cable that I rewired to plug into the Mac and provide the correct voltages. That wasn't too bad. But then I needed to add more wires and a connector for the video signals coming out of the Mac side. And since the video signals needed to include ground, I had to cut and splice the Mac's power wires for that. Then I needed to wire in another header for +5V and GND to power the RPi Pico, which involved more cutting and splicing. Finally I added yet another header for connecting an 8 ohm speaker for audio. The whole cable assembly took me many hours to finish, and it looks like a... big mess of wires. It's ugly as hell.  Joe's Computer Museum sells an adapter PCB that duplicates the function of my ugly cable harness. I probably should have just bought that. Honesty time: I've lost sight of whatever my original purpose was for doing this. I thought it might be handy for troubleshooting logic boards without electrocuting myself on a live CRT, but more importantly I just thought it would be neat and maybe it would be a good Mactoberfest display. But now that I've done it, it's pretty awkward to set up and the results aren't quite what I'd hoped. | |
| Posted by: arroz on 2026-10-06 13:18:10 Hi! Shameless plug (although I'm not selling anything and don't have a SoundCloud 😄) but I have a similar setup using MacDVI, the adapter I built to do the same but with a fully digital signal, outputting over DVI (HDMI cable). Instead of 640x480 (which is not a good resolution for this), I use 1024x768. 1024 is twice the horizontal resolution of the Mac (512), so the adapter does pixel doubling without loosing any quality. It works on 128/512/Plus, SE and SE/30 according to folks in this thread, and more recently on the Mac Classic that has a slightly different video signal. No config or calibration necessary (aside from an extra wire on the Classic), it handles everything automatically. I'm working on supporting the Classic PWM brightness, but still didn't have time to fix some issues. Regarding power, I'm using a borrowed PicoPSU. Wires were soldered directly to the PSU (it should be a proper ATX plug, but…) and then I built two connectors, one for the Mac Plus, and more recently one for a Mac Classic. It's a really good setup, allows me to test these boards, FDDs, etc without caring about all the analog and CRT stuff. My final goal is replacing the CRT on my Mac Plus with one of these displays (I already have one), but I have to design a PCB to replace the analog board, where I will bolt a MeanWell PSU, the Pico, speaker, and a few other things. Regards, Miguel Arroz | |
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