• Please review our updated Terms and Rules here

Hook up an Imac to XT

J

JT64

Experienced Member
Joined
Oct 21, 2008
Messages
402
Location
Sweden
Right now i run my XT on a MCGA monitor with the onboard graphic, but i would like to use it with a VGA card and monitor i have a VGA card.

I'm offered a Imac to pickup.
Can i unhook the Imac monitor and attach it to a Mac VGA adapter, will it synch with the XT?(And maybe a monitor switch)

JT
 
imac

imac

JT64 said...Imac monitor
Click to expand...
Aren't iMacs those cute little translucent all-in-one macs, or is it seperate monitor ?
Does the monitor have the same connector as your VGA card ?
Over here, you can literally find old VGA-style monitors in the trash as people switch to flatpanels. Does your modern computer use an analog VGA monitor, or a digital DVI one ?

patscc
 
patscc said:
Aren't iMacs those cute little translucent all-in-one macs, or is it seperate monitor ?
Does the monitor have the same connector as your VGA card ?
Over here, you can literally find old VGA-style monitors in the trash as people switch to flatpanels. Does your modern computer use an analog VGA monitor, or a digital DVI one ?

patscc
Click to expand...

I have a 22 inch LCD with both DVI and VGA that we use with our computers. But i have a slight memory of blowing a CRT monitor by setting the switches wrong on the VGA card 10 years ago. And i dont think i want to take the fight with my honey if that would happen again :mrgreen:.

Ive looked around quite abit in neigbourhoods electronic trashbin lately :-D
Even brought up an 15 inch dell that looked promising, but it turned out to be a wreck, the powerlamp just kept on flashing. Looked for troubleshouting on net but no simple solution in sight, available.

And still looking every time i throw garbage :twisted:, last time i got a Di-624 router with malfunctioned poweradapter, i was lucky got a spare and probably only was broken powerchord anyway. To bad doesnt support DD-WRT so no wireless bridge in sight yet.

But back to my idea, i beleive it is possible to disconnect the video out from motherboard of an imac G3 and that the connector is a 15 pin old standard mac connector, from what i decrypted reading about G3.
An apple to VGA adapter should be easy to aquire.
But i am not sure if it support VGA refresh rates.

If anyone live nearby Linkoping sweden and have a monitor just standing, i am willing to drop by pick it up. Ive looked around on Tradera and Blocket for freebies in the surrounding and neighbourhood basically.

But no real luck so far.

JT
 
LCD Panels

LCD Panels

Modern LCD panels rescale all signals anyway, they simply display "bad signal" or something like that if the timing is not accepted. If it's a VGA (with 15-pins) card you're hooking it to, it's very unlikely you'll blow it. My XT & PC I'm currently fiddling with are hooked to a flat panel.
On the iMac, that depends if the drive circuitry for the tube is on the mainboard or not.
I'll look around and see if I can find one to take a peek at. What model iMac is it, anyway ?

patscc
 
Last edited:
it depends. Is the monitor in the Imac fixed frequency? If so is it's native resolution 640 x 480 or 832 x 624? If it's the latter, you're out of luck, because that monitor is expecting a ~48khz signal, and VGA (at the low end basic modes) puts out 31.5khz. Even if you got the proper connection going and the monitor runs in a Mac's 640 x 480 mode, you'll still need to tweak the horizontal hold (as it would be known as in a tv set) or horizontal scanning frequency, because the Mac's *low res* operates at 36khz IIRC (maybe 35khz). You should be able to make the adjustment I would think.
If you can accomplish all that, you can move to the head of the class. MPOI get the Dell monitor operational. It'll probably be easier. The Imacs seem like a royal pain to get into (though I've barely tried).
those monitors in the Imacs couldn't be multiscanning, could they? Remember both the VGA and Macs typically utilize a few pins to tell the computer what type of monitor is connected (sense pins). You'll need to gather all that relative data.
 
tipc said:
it depends. Is the monitor in the Imac fixed frequency? If so is it's native resolution 640 x 480 or 832 x 624? If it's the latter, you're out of luck, because that monitor is expecting a ~48khz signal, and VGA (at the low end basic modes) puts out 31.5khz. Even if you got the proper connection going and the monitor runs in a Mac's 640 x 480 mode, you'll still need to tweak the horizontal hold (as it would be known as in a tv set) or horizontal scanning frequency, because the Mac's *low res* operates at 36khz IIRC (maybe 35khz). You should be able to make the adjustment I would think.
If you can accomplish all that, you can move to the head of the class. MPOI get the Dell monitor operational. It'll probably be easier. The Imacs seem like a royal pain to get into (though I've barely tried).
those monitors in the Imacs couldn't be multiscanning, could they? Remember both the VGA and Macs typically utilize a few pins to tell the computer what type of monitor is connected (sense pins). You'll need to gather all that relative data.
Click to expand...

Well this is pretty much what i found out about imac monitor / support.

# VRAM: 8 MB SGRAM
# Video: supports resolutions of 640 x 480, 800 x 600, and 1024 x 768 using ATI RAGE 128 VR chip set and 2X AGP
# monitor: 15" (13.8" viewable) multiscan to 1024 x 768

There is some linux configuration files available for imac G3 maybe one can figure out the hsync vsync from them.

JT
 
patscc said:
Modern LCD panels rescale all signals anyway, they simply display "bad signal" or something like that if the timing is not accepted. If it's a VGA (with 15-pins) card you're hooking it to, it's very unlikely you'll blow it. My XT & PC I'm currently fiddling with are hooked to a flat panel.
On the iMac, that depends if the drive circuitry for the tube is on the mainboard or not.
I'll look around and see if I can find one to take a peek at. What model iMac is it, anyway ?

patscc
Click to expand...

I worry about that the card somehow is able to put out some weird signal standard over VGA port.

Chips on card is WD90C11-LR and TR9C1710-xxxxx (need googles)
And here is a real bad picture below.

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=964&d=1226371124

Found slightly relating posts below
http://archive.netbsd.se/?ml=cctech&a=2007-01&t=3042832

But I think i had it working in an eight bit slot many years ago.

The imac is a G3 i do not have model number yet have not picked it up.
But the color ruby indicates it is either a 400 or 450 Mhz cpu.

JT
 
Ruby G3

Ruby G3

Here's a link to how to take the G3 apart.
http://www.scribd.com/doc/103447/iMac-G3-Disassembly-Guide
I took a look at it, and the analog video portion is combined with the power board. The connections from the video/power board to the logic board don't look like anything standard.
That's not to say you can't figure it out, but at that point, you might be worried about frying the XT.
I appreciate the motivation, though, to take a iMac G3 & gut it to use as a monitor on an old XT. Why not put Linux on it ?

patscc
 
Yep, I have a iMac sitting here. I put linux on the one I have. I don't remember what the speed of the processor is in mine but nothing earth-shaking.

Anyway, as stated, using the iMac monitor for something else would be fairly complicated to pull off. I don't think you would be happy with the result. It is a really bad design as far as too much internal heat. Those Apple guys sure must HATE the sound of a fan! Almost from day 1. I have the external fan unit on my Apple IIe, the standard one that doubles as a power strip.
 
JT64 said:
I worry about that the card somehow is able to put out some weird signal standard over VGA port.
Click to expand...

which card? The Imacs? Umm, you may actually have a point, but I'm not sure/don't remember exactly. The old school fixed frequency monitors required negative sync signals IIRC, and the Macs plugged right into these. I watched a guy more or less connect a 486/early pentium right up to one, but he may have fiddled w/some settings (the cards that came out in the mid to later 90's had LOTS of user configurable bios options, like specifying the polarity of the syncs, etc.). So that monitor may be looking for a negative signal, while a VGA puts out positive? In any event it's no big deal to invert the signals. There's bound to be specific info on that still on the web, or join a yahoo or goodle group (electronics_101 on yahoo is a very good place to get many questions answered. It may be as simple as using a hex inverter chip (7406?), but you'll want to know for sure what's entailed so you don't damage the monitor.
So you got a multisyncer. Congrats. Whether it'll like syncing down to 31.5khz remains to be seen. Listen for any odd noises, transformer making strange noises or whatever. I think the major problem would be the flyback transformer (not designed for that frequency) but I'm hardly an expert. No big loss if the thing blows up I guess LOLOLOL.
That card is one of the most basic ones out there. I wish I had 10 more! It will work in either an 8 or 16 bit slot/machine.
Good luck and don't kill yourself. Don't touch the anode (lead going strait into the crt near the top). And avoid touching any components, but especially capacitors, especially the larger *cans*.
 
I have ventured into the iMac CRT, as I've had to repair one before (burnt out flyback).

They are a semi-fixed frequency CRT. They are fixed in that they only can take a grand total of THREE scanrates, and that's it..

640x480 @ 117Hz
832x624 @ 95Hz
1024x768 @ 75Hz

All with an average of about 58KHz horizontal frequency.

Now, on the Bondi blue iMac, you can EASILY tap into the video and get the CRT to run. Only fault, the iMac's mainboard must be on for the power to the CRT to even work (it's the same PSU). They use the standard Apple DB-15 video connector. But of course, you must input video at one of those scan-rates, or the CRT will cry out (really, it whines)...
 
evildragon said:
I have ventured into the iMac CRT, as I've had to repair one before (burnt out flyback).

They are a semi-fixed frequency CRT. They are fixed in that they only can take a grand total of THREE scanrates, and that's it..

640x480 @ 117Hz
832x624 @ 95Hz
1024x768 @ 75Hz

All with an average of about 58KHz horizontal frequency.

Now, on the Bondi blue iMac, you can EASILY tap into the video and get the CRT to run. Only fault, the iMac's mainboard must be on for the power to the CRT to even work (it's the same PSU). They use the standard Apple DB-15 video connector. But of course, you must input video at one of those scan-rates, or the CRT will cry out (really, it whines)...
Click to expand...

I can not imagine the card be able to put out none of the above, wasn't standard VGA scanrates 60 hz those days. Maybe it could actually put out 75 hz but i doubt that the 1024*768 will work unless my card have one meg ram.

JT
 
evildragon said:
I have ventured into the iMac CRT, as I've had to repair one before (burnt out flyback).

They are a semi-fixed frequency CRT. They are fixed in that they only can take a grand total of THREE scanrates, and that's it..

640x480 @ 117Hz
832x624 @ 95Hz
1024x768 @ 75Hz

All with an average of about 58KHz horizontal frequency.

Now, on the Bondi blue iMac, you can EASILY tap into the video and get the CRT to run. Only fault, the iMac's mainboard must be on for the power to the CRT to even work (it's the same PSU). They use the standard Apple DB-15 video connector. But of course, you must input video at one of those scan-rates, or the CRT will cry out (really, it whines)...
Click to expand...

What is your bet on other colors do they also have the DB-15 connector, i guess it is located on the motherboard?

JT
 
I don't think it'll work at all. The PC would boot in about 720x400 70Hz, which would be enough to hurt the CRT.

as for other colors, I believe they went with an internal connector pin header..
 
evildragon said:
I don't think it'll work at all. The PC would boot in about 720x400 70Hz, which would be enough to hurt the CRT.

as for other colors, I believe they went with an internal connector pin header..
Click to expand...

Ok that close that project. But maybe i still want an imac :confused: god now for what good reason.

By the way nice computer setup, i wait for my SB16. Maybe i actually have a V30 CPU, because i think in run close to 10 Mhz and it is definitly not a 286.
I actually have one 1024 MB drive in my, at least i can partition one primary and one extended partition using one ide channel, on the other ide channel i have a compactflash adapter work real great i must say.
I have them connected to ADP50L ide controller, what controller do you have?

What equaliser program do you use, is it something that come with SB16, do you know if the midi port is working?

JT
 
It came with the SB16 driver. It's merely the treble and bass controlls. MIDI works cause I've used it to download patches to my Yamaha DX7.
 
patscc said:
Why would it start up in 720x400 70Hz ?

patscc
Click to expand...
That's what RAMDAC uses for the usual 80 column DOS text mode. It's a 720x400 raster. It's not like VGA can send text to the screen like a dumb terminal. It has to send it out as lines of graphics to the CRT. It scans at 400 lines visible, with approx. 720 pixels wide (though not definite.)..

Any modern day monitor can tell you this, even virtualization shows text mode as 720x400 too.
 
Vesa

Vesa

I'm not denying it's a possible mode, but isn't the 70Hz refresh rate something that would get negotiated across the DDC channel with a VESA-compliant monitor ? I can certainly see pushing a VGA adapter to run that resoution, but I don't think a standard, old-fashioned VGA card is going to default to that, especially since 720 x 400 at 70hz isn't a mode reachable by the XT's INT 10h calls. (Or am I mixed up ?)

patscc
 
You must log in or register to reply here.
Back
Top