External Compact Mac CRT

[Gorgonops]

The video circuit seems pretty crazy stuff - does it output a standard composite video signal? That would be pretty easy to convert into VGA!

No. If you read the fine print he says he figured out a modification he could do to an Apple composite monitor that would up its line rate sufficiently to sync with the Mac's output. Remember, the Mac's output simply won't *fit* on a monitor using standard NTSC sync; it only allows for 262.5 vertical lines per non-interlaced frame (technically broadcast NTSC is 525 line *interlaced* using two half-frames) which of course the Mac outputs a picture 342 lines + some blanking lines tall.

There are industrial composite monitors that would be willing to accept that signal unmodified: here's an example, you can order it with a 21khz sync rate, that should work right off the shelf.

 

[Trash80toHP_Mini]

That's some interesting stuff! Seems like someone has preceded us by almost three decades in successfully having a 128k logic board running without its AB.

<snip>

Also the power supply seems a common ATX one of some sort . . .

That would have been ISA, such was the world of the Cat Mac/Hackintosh, all inexpensive, Industry Standard HARDWARE hacking! Debasement of the time honored latter term for almost mere OS trickery is an abomination.

 

[Sherry Haibara]

I'm sorry, I'm not really practical with all the standards that were used back then. I know that ISA was a standard card interface used by a lot of IBM clones in the mid-80s, but I'm not accustomed to power supply standards and so forth!

I've read about the IIGS monitor, but I haven't ever owned one, so I was not sure about the connector and sync/refresh rates it used, I assumed it must have been some sort of composite/antenna signal just by looking at the circuit output.

So basically, an industry specific monitor would be needed for that hack to work? Would it be possible to re-use it in some ways with more common CRT screens as found in TVs and old multiscan monitors? NTSC monitors won't like such a signal as you pointed out, but I'm wondering if it's possible to obtain something less-exotic than an industry grade monitor or if we are forced to do some post-processing to that signal.

 

[Trash80toHP_Mini]

No worries, no criticism intended, I only get upset with upstarts who've hijacked a perfectly suited hardware hacking term for sleight of soft hands.

ISA would be the entire (IBM PC AT) architecture: I/O Cards, Box, MoBo, MoBo specific backplane openings (where implemented at all) PSU and those specific Power Connectors pictured that finally settled down into the ATX/PCI form factor after much ado.

Such passed for standardization in that 8/16bit AT day and on thru the VESA Local Bus, pre-PCI era of 32bitdom that developed by the Clonemakers (Gang of Nine) after some upstart in Cupertino went all 24/32bit over the entrenched PC industry. The gang went one way after a lot of false starts, while IBM MicroChannelled itself into . . .

. . . well . . . lets face it . . . Lenovo.

.

 

[Gorgonops]

So basically, an industry specific monitor would be needed for that hack to work? Would it be possible to re-use it in some ways with more common CRT screens as found in TVs and old multiscan monitors? NTSC monitors won't like such a signal as you pointed out, but I'm wondering if it's possible to obtain something less-exotic than an industry grade monitor or if we are forced to do some post-processing to that signal.

Well, the IIgs monitor *is* a standard NTSC composite monitor, but the author of that article hacked it to accept the higher scan rate. Undoubtedly it's possible to do that with other monitors, but, yes, you're unlikely to run into "just any" composite monitor that's willing to take it. There are some "multisync" composite monitors out there, mostly designed to handle both PAL and NTSC signals, but the Mac's output signal is going to be way out of spec for PAL as well so I doubt many of them will be forgiving enough to handle it.

Just to note, it's actually possible to get monochrome Composite Video out of a VGA card using just a few resistors; I built one of these adapters on a lark once. The thing is you have to use a driver to reprogram the VGA card to output an interlaced picture at NTSC scan rates. Alas there's no way to reprogram the Mac's video hardware (short of attacking it with a soldering iron) to be more friendly.

 

[wilykat]

that 32-bits VESA was still a pain to work with.  It wasn't very well designed to handle more than 1 card.  I've had display get corrupted and hard drives not work because of capacitance and interference.  It took me quite a while to find a 32-bits video card and 32-bits IO card that worked together for my then 486DX2.  I'm glad they went PCI which behaved a whole lot better shortly after rather than try to keep the overly long and flaky 32-bits slot and added an extra 32-bits upgrade