se/30 and/or other classic Mac video output direct conversion

[Chopsticks]

just wondering if anyone knows much about getting Video output from these old classic Macs directly from the logic board harness, correct me if im wrong but I think the se/30 has some form of a composite out pin as well as (I think) h/v-sync pins... so im wondering about if its possible to adapt those signals to a modern display. Im sure ages ago I read about the signal being TTL and maybe needing to be inverted but its just an idea that popped into my head and I wanted to see if anyones done this before or knows of and information about it on the web that could be used as a starting point for investigation

 

[cheesestraws]

getting Video output from these old classic Macs directly from the logic board harness

I seem to remember there's a circuit in the first edition of "Build your own macintosh and save a bundle" (what a name!) to adapt the internal video signal to something more TTL-like.  How well it works I don't know, I've never tried it.  Note: in the second edition of the book it isn't there any more, because there was available at that time a pre-made and easier option; but obviously that pre-made and easier option has vanished like a shadow from availability.

I believe you're right about the inverter too.

 

[Chopsticks]

I seem to remember there's a circuit in the first edition of "Build your own macintosh and save a bundle" (what a name!) to adapt the internal video signal to something more TTL-like.  How well it works I don't know, I've never tried it.  Note: in the second edition of the book it isn't there any more, because there was available at that time a pre-made and easier option; but obviously that pre-made and easier option has vanished like a shadow from availability.

I believe you're right about the inverter too.

thanks for the info!
I'll have a look and see what I can learn from that book

 

[MrFahrenheit]

I had asked a similar question earlier this year because I wanted to be able to test compact Mac motherboards outside of the case. I was told the video output signal isn’t compatible with anything because of its refresh rate. I’d love to see a modern device made that plugs into the connector and offers some form of video out. 

 

[cheesestraws]

I’d love to see a modern device made that plugs into the connector and offers some form of video out. 

I'm wondering if you could rig it up something like the OSSC to render it a bit more acceptable to modern displays

 

[MrFahrenheit]

I'm wondering if you could rig it up something like the OSSC to render it a bit more acceptable to modern displays

Where an adapter board could be useful is if someone used the board schematics of the SE or SE/30 (like is being done in another thread) to manufacture a replacement board. Imagine buying a 2020 made SE/30 board and using an adapter board to put it onto a small case with VGA output (obviously intercepting and converting the signal). 

 

[Chopsticks]

I'm wondering if you could rig it up something like the OSSC to render it a bit more acceptable to modern displays

I have an ossc but being that is purely a RGB scan convertor, im not sure that is would even be possible to use that with the composite output of the se/30. if I can find enough specs onfo regarding the type of composite signals (and the h/v-sync) coming form the logic board then making an adaptor shouldn't be that difficult. as for the refresh rate timing well there are options for converting scan rates to more modern frequencies, it just depends what those are really. I do need to download and read that book Cheesestraws mentioned above so hopefully that will shed some light on this a bit further

 

[cheesestraws]

not sure that is would even be possible to use that with the composite output of the se/30

You may well be right, that was me making it up merrily as I went along.  Was wondering whether you could trivially split the monochrome signal out into three identical (r,g,b) signals and scale it that way.  But I have no idea if that would actually work.

 

[cheesestraws]

You might find this useful, though it is the other way round: there's code here to essentially bitbang video from a BeagleBone Black to a compact Mac screen:

https://github.com/osresearch/classicmac

 

[aeberbach]

Actually I am working on a thing to do this. I have the video from my SE/30 brought out to a header on the rear slot and have made sense of the output with the oscilloscope. I am working on various display schemes (VGA first) using a MAX10 FPGA. The MAX10 is not expensive but is a little bit overkill for this job - a nice thing about it is that it has configuration memory built-in so no external flash is required to boot. Unfortunately it is 3.3V I/O but not many level converters are required. There's a CPLD which is 5V available, but four times the price and long-term availability is unknown. I'd like to make a PDS video card for modern output eventually.

 

[Chopsticks]

Actually I am working on a thing to do this. I have the video from my SE/30 brought out to a header on the rear slot and have made sense of the output with the oscilloscope. I am working on various display schemes (VGA first) using a MAX10 FPGA. The MAX10 is not expensive but is a little bit overkill for this job - a nice thing about it is that it has configuration memory built-in so no external flash is required to boot. Unfortunately it is 3.3V I/O but not many level converters are required. There's a CPLD which is 5V available, but four times the price and long-term availability is unknown. I'd like to make a PDS video card for modern output eventually.

that sounds really interesting, do you have a forum threat here or anything where i can follow your project?
i was mainly just looking into this out of curiosity, but if you're already working on something that i can read about then that would more then satisfy my interests

 

[360alaska]

This would be a start:

 

[360alaska]

Then, Maybe something like this to convert the MDA:

 

[Chopsticks]

yes that looks like the way to go, convert to a TTL Digital signal that can then be converted to analogue rgb vga

 

[cheesestraws]

Yeah, think you're probably right.  IIRC, the issue with connecting it to TTL monitors was that the timing was somewhat skewiff relative to what a PC monitor expected, not that the signal is electrically incompatible.  Modern stuff should be easier to tweak in that regard, one would hope...