Video on G3 slot loader

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Ex-parrot's picture
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Joined: Dec 20 2003
Posts: 6835

I'm trying to get an old 305mhz SL iMac board working minus the iMac... and I've run in to a problem with the video.

I've made an adapter to connect from the video port on the board (the one that normally goes to the analog board) to a VGA socket, in several different ways (crimping, soldering) and both times I get a rolling picture that my monitor can't sync to...

so the question is: does anyone know what the sync frequencies are that the iMac is putting out? And whether I can change this to allow my monitor to work Smile

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Michael

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When i used to run external m

When i used to run external monitors on mine, i found that the 1024 x 768 setting was the only one my monitor could use because it would slow the freq down to i think 75hz or 85hz, anything lower for res has freq up over 100hz AFAIK. if your already running it that high and your monitor cant sync then there may be a problem with wiring, i never did the atx hack so i dont know much about that.

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-Justin
(dead) PB100, Q650, PB Wallstreet, beige G3, Imac snow 600, Ibook g4, SE30, (dead) IIsi, TiBook 667VGA, PBg4 1.5, MDD dual 1.25ghz, 1.8ghz g5 tower.
OS7.5 to 10.3.9. I LOVE CLASSIC MACS!

Eudimorphodon's picture
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Joined: Dec 21 2003
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Refresh Rates...

(A bit of googling to remind me...)

The iMac's internal monitor supports these resolutions:

640x480 at 117Hz refresh rate
800x600 at 95 Hz refresh rate
1024x768 at 75Hz refresh rate

You actually need a fairly capable multisync monitor to handle these. Something too cheap or too old won't do. If you're not already using one try hooking the machine up to a more expensive recent-vintage CRT. (Any 19" or bigger CRT less then seven years old should do, while a bottom-of-the-barrel 17" or smaller might not be capable enough.)

As for changing the refresh rate, I think you might need a software hack like SuperRes/SwitchRes/DisplayConfigX on a slot-loader motherboad. With the tray-loaders just booting it once with an iMac-frequency-capable monitor was enough. (Having a VGA adapter plugged in will render it "unlocked". I don't know what the sense line arragement is, if any exists at all, on the slot loaders.)

--Peace

Eudimorphodon's picture
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Joined: Dec 21 2003
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One other thing...

It's also been noted by people doing *slot* loader conversions that the signal strength from the internal video connector is fairly weak. Ex:

http://www.cryogenius.com/hardware/imac/

I suppose it's possible that even if your monitor is "capable" of displaying iMac video modes it might have a problem with the signal level getting to it.

--Peace

Ex-parrot's picture
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So I found an old 14" monitor

So I found an old 14" monitor that'll sync to it... better than nothing and it fits quite well on my desk....

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Michael