VGA hack -- sense line modification

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tmtomh's picture
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First off, come on folks! Every other Forum on AF 2.0 is up and running and the old forums are starting to whither away -- except with us CC hackers!

So to help start things off, I have a comment about VGA hacks.

My main comment is that after completing my first successful VGA hack, I'm a proponent of doing the sense-line modification in the wiring harness rather than on the analog board. My reasons are as follows:

(1) It's much easier, with very little risk. I ruined one a/b trying to do the sense-line mod on it. It's really cramped, and it's virtually impossible to figure out what's wrong if it doesn't work (continuity tests indicated it should work, but it didn't). By contrast, doing the mod in the harness requires a simple snipping of a few wires, and then just twisting two of them together (with solder, a small wire nut, whatever).

(2) It makes testing easier. I discovered that an unmodified a/b will display VGA if you have already done the sense line mod on the wiring harness. The image will be too narrow, with approx. 1 inch black borders, but it will be sufficient for confirming the success of the sense line mod. And if (like me in this case) you're using an untested a/b, it will allow you to confirm the a/b works before you go to the trouble of modding it.

The only downside I can see to doing the mod this way is transportability. If you want to move the analog board to another CC, you have to move the harness too, or else repeat the wiring harness mod on the new CC.

So what do you all think?

Matt

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I also have been wondering wh

I also have been wondering when there would be an official migration of the CC forum. Thanks for starting the ball rolling.

I think your reasoning is sound. I have also looked at the a/b pins and thought to myself that all but the most expert solderers would have to be nuts to try and solder in that cramped space.

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jt
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Which harness are you modding for what MLB?

If you're talking about a CC compatable MLB/harness that makes sense (so to speak) so I'd agree with your reasoning. If you're talking about a 630/6360 5XXX harness that has the connector/ribbon cable for the monitor out card, you ought to be able to create a header based adapter and the mod could be moved along with the MLB. However, you'll be tweaking the CRT to display full screen anyway, so would it really matter? As I understand it, you'd need to replace the MLB with another VGA capable board anyway, no?

Some day I'll have a CC! Undecided

jt

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tmtomh's picture
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Clarification on harness

Yes, jt, you're right -- I wasn't being as clear as I should have.

I did my VGA mod in the context of making a Mystic. So I was modding the CC's original wire harness (the Mystic's 575 mobo plugs right into the original CC harness).

I agree 100% that if one is making a Takky and therefore using a 630/6360/5500 replacement harness, the question becomes kind of moot -- although again, since mating the 630/6360/5500 harness to the CC analog board connector requires a bunch of custom wiring anyway, why not leave the sense line solder points on the CC a/b alone and just make the adjustment in the harness?

Finally, jt, my condolences on your CC-less existence. Don't despair -- I'm sure you'll find one for a reasonable price sooner or later!

Matt

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Ultimately... does the analog

Ultimately... does the analog board need to sense that 640 mode is in operation or is it the video card? I think the video card needs logic to tell what mode it can display. Is this thought correct? If so, I need to be able to tell a Radeon or Geforce PC card to run in 640 mode only. Am I going to do this for the analog board and the video card??

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The sense wire mods are for t

The sense wire mods are for the benefit of the video card - or, in the case of a CC, the logic board which produces the video signals.

Stuart

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Jon
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VGA based cards doen't unders

VGA based cards doen't understand sense lines, IIRC. They would need to be told through software what resolutions to use. The sense line tell the video what the display is capable of, and when using a sense line enabled setup (Mac DB-15 video, worktstation 13W3 video, ADC?) the sense lines can prevent the video fromoutputting a signal that the display can't handle to prevent damage to the hardware. If a VGA based video card is capable of outputting a very high resolution mode with a high refresh rate, it will do so happily if told to by software, even if it is only a 640x480 VGA display hooked up. And chances are that the display will be fried too.

Jon.

No one should be protected from the effects of his own stupidity. - Anton Szandor LaVey in 1988 (There is a certain irony in this quote... Tongue)

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But most early versions of Ma

But most early versions of Mac OS, when 'told' by the sense wires that the hardware is driving a VGA screen, will actually refuse, or at least make 'un recommended' anything beyond 640 x 480 at a low refresh rate.

Stuart

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metzen01's picture
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Question about the sense line mod

I want to perform this sense line mod I would like some images for reference. I'm not sure if anyone can take some snapshots of them and email them to me at . I also was curious about performing this mod to the wiring harness. I've already performed the first part of the VGA Hack so will I be able to still continue with the wiring harness part or take a risk and mod the rest of the A/B?

metzen01's picture
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Was able to figure out what I needed to do next.

So I was able to continue on with the VGA Hack. I didn't need to look at the wiring harness but instead the fan connector locations. *Crossing Fingers*

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Question about Wiring Assembly videio connection

I've performed the VGA Hack on my color classic and i have an imac rev a motherboard. I wanted to know how technical it is for one to connect the video cables from the imac video connector to the Color Classic to the wiring assembly. I had read a posting here about the topic.
http://www.applefritter.com/node/4801

This mentions extending the cables on the wiring harness and I wanted to know what kind of connector or process in general is used. If you have any helpful pictures I'd appreciate it. Sorry in advance if I am terming things wrong for this process.

I've sent a private message to doogie1303 because he's successfully finished this particular mod but I'm afraid that he's moved on to newer projects and does not check this site as often as before.

Any help is appreciated!!

Robert