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Does the LC III support RS-170 NTSC?

Gorgonops

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Staff member
Recently I've acquired an LC III in unknown condition. It chimes and sounds like the HD is booting, but I don't have a monitor adapter. I've ordered one, but in the meantime I stumbled across an explanation of how the NTSC mode that's built into some Mac II-era cards/machines is set up. It included a schematic for a cable to get mono composite video from pins 5 and 6 by tying the sense lines 4, 7, and 11 together, so just for laughs I made an adapter and gave it ago.

TL;DR, it didn't work. I looked in the devnote for the LC III and it has a monitor support matrix in which the NTSC mode is not to be found. Anyone ever try it and get it to work, or am I in suspense until my adapter arrives? (Or I chop up a VGA cable, I guess.)

 

Gorgonops

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Staff member
I'm guessing from the crickets no one has ever tried this before.

More digging around has convinced me that this is *probably* unsupported on this hardware. There are a couple tantalizing mentions of NTSC/PAL in the "Service Source" but no actual indication as to what sense line combination different from that apparently supported by NuBus video cards (and it looks like possibly "real" Quadras like the 700 and 900/950?) might convince the machine to output them.

Honestly I'm kind of wondering if the LC III's video chip even supports sync-on-green, which would be a prerequisite for the wiring schema I followed. The pinouts in the technote don't mention it, and I've picked up some hints that at least some of the LCs needed a special cable or adapter to work with the original Apple 13 color monitor. I wonder if said cable tied the separate sync output to green with a resistor like the mono composite output wiring scheme for VGA cards that's floating around. (And I tried once with success many a moon ago.)

 

Gorgonops

Moderator
Staff member
... it actually just occurred to me if the sense line combo for NTSC is the same as the NuBus cards but sync is separate you'd see what I saw with my adapter, which is squat. I wish I had a scope with a frequency counter, I kind of want to probe the sync line now.

 

Gorgonops

Moderator
Staff member
My monoprice adapter should be here by Wednesday so I'll wait, this was mostly about "wow, if it can output NTSC that would be cool!". ;)

It'll be a pleasant surprise if the machine actually works. The chiming and clunking is sounding promising, at least. Also, when I was turning out boxes in the garage looking for an adapter I found what I'm pretty sure is a 32MB SIMM; I plugged it in and it still chimes and clunks so, yay, maybe also promising!

 

Gorgonops

Moderator
Staff member
this was mostly about "wow, if it can output NTSC that would be cool!"
(I mean, seriously, I was sort of dying to post a picture of a Mac desktop displayed on my Apple IIc's monitor. It's already lived through the indignity of having a Tandy 1000's BIOS messages pumped through it, though, so maybe that's just as well.)

 

Gorgonops

Moderator
Staff member
I guess I failed to get NTSC video out of it, but on the bright side my LC III seems to be in decent health: (Monitor adapter showed up today.)

LCIII-Alive.jpg

I imagine to be safe I should prepare to proactively recap it, but for right now it's chiming and the board looks pretty clean so, yay! I'm particularly pleased that the SIMM I found rattling around loose in a cardboard box without an anti-static bag seems to work fine. Next job is to try it out on the network, I guess.

 
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