Controll Mac Color Classic display with a Raspberry Pi - Page 1
Forum section: electronics / projects

author: samNt
author_rank: Newbie
timestamp: May 30, 2021, 07:40:52 am
content: Hello,I'm not sure if this is the right place to post this but I'm wondering if anyone could give me any help with this as my knowledge of electronics is rather limited.I have a Mac Color Classic that has no motherboard and I thought it would be cool if I could use it as a third monitor for my computer (it has a Trinitron display!) After doing a little searching online I found this blog post about using a Raspberry Pi 4 to control a Mac Classics displayhttps://nerdhut.de/2020/03/17/raspberry-pi-dpi-control-crt/. The Mac Classic has a monochrome screen with a resolution of 512 × 342 and the Color Classic has a colour display with a resolution of 512 × 384. I figure that the guide I have linked would be mostly applicable to the Color Classic. I assume the main differences would be the timings (as the resolution is different (not sure about the refresh rates)), hooking up the other colours (using resistors to change the intensity for the different bits of each colour.) I assume that it would be similar in terms of voltages. That is 5 for HSYNC and VSYNC and 3.3 for the colours.Anyway what I'm wondering is does anyone see any problem with this and if not does anyone know what wires to connect up to the Pi as I'm not sure what wires are for what and of course the guide I've linked is for a different display. Also I'm aware that the CRT acts like a big capacitor and can have very high voltages.I've attached a couple of photos of the CRT (don't know if that will be of any use.)

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2021, 09:35:26 am
content: No, the approach used for the Classic display makes no sense for the Color Classic.Instead, just drive the Color Classic’s display as a standard VGA display.FYI, a common hack to the Color Classic was to modify the display to 640x480 (at 67Hz), which was the minimum resolution for a lot of games. So at minimum, you know the drive circuits can handle that.The mod normally involves two parts: 1. modding the analog board to change its horizontal deflection voltage, so that it works at the higher resolution, and 2. modifying the display resolution sense lines so the logic board sees it as a different display model.In your case, only the first mod is needed, since a Rpi doesn’t know how to read the old-style Mac sense lines anyway.It’s the mod referred to as step 1 of “option 1” here:https://powercc.org/640x480/This page has the pinouts of the backplane connector:https://powercc.org/takky/

author: samNt
author_rank: Newbie
timestamp: May 30, 2021, 11:39:58 am
content: Okay and thanks for your reply. I'll have a look into the mod you mentioned. I was actually aware of it but I read somewhere on a forum that it didn't actually make it work with VGA and the person thought that the people/person who came up with the mode just called it that because they associated 640x480 with VGA. Anyway as I don't know much about it I thought it wasn't worth looking into any further.Also with regards to the VGA mod/s I've read that it increases the voltage to move the beam faster (or something along those lines) and some people seemed to think it might put extra stress on the circuitry. Do you think that would be much of a problem.Sorry if theses are stupid questions. As I said I don't know too much about electronics but I very much appreciate your help!

author: samNt
author_rank: Newbie
timestamp: May 30, 2021, 11:42:25 am
content: I just quickly looked at the page 8.4V doesn't sound like too much extra (I mean I know that's not very scientific of me to say)