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Color Classic VGA Mod. the CORRECT way


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Also, it shouldn't be possible to do 640x480 @ 16-bit. That would be 614.4k of VRAM. The most you can have in a CC is 512k. How does the system handle the difference in available vs. needed VRAM? Does it dip into system memory? Is it even capable of doing that? It doesn't seem likely, since the default video modes for the CC all fit easily within the maximum available VRAM.

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On 4/10/2019 at 1:53 PM, Paralel said:

Also, it shouldn't be possible to do 640x480 @ 16-bit. That would be 614.4k of VRAM. The most you can have in a CC is 512k. How does the system handle the difference in available vs. needed VRAM? Does it dip into system memory? Is it even capable of doing that? It doesn't seem likely, since the default video modes for the CC all fit easily within the maximum available VRAM.

I have upgraded this guy to a Color Classic II logic board(couldn't stand the gimped stock CC performance) and with the 256K expansion I have 768K VRAM.

 

As for screen distortion, it's the photo and I'll try to get a better one. I'm upping the dissipation rating of a resistor that is dissipating too much at the moment and when that is done I will get better photos. It does curve a bit at the top of the screen but it appears to be normal as it did it before on another analog board and is also something I notice in photos of other machines.

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I thought I'd add this little update. This mod seems to be working just fine so far on the Rev D board outside of a warm reboot sync problem that I can't trace. None of the ICs or resistors, outside of the really hot area below, get above ~115F so it shouldn't be drift or anything like that. Leave the machine off for a few minutes and it syncs right up and works for hours without a problem. It just seems to need shut down, not powered off, so the problem is unrelated to RF11.

 

I upsized RF11 to a 3 watter and it runs at about 250F now but CF8 just runs hot I guess. That whole resistor/capacitor/zener diode area runs as long as the switch on the back is turned on so that electrolytic sits at about 65C(measured by attaching thermocouple). It's not comfortable to touch but well within specs, especially if you swap it out for a 105C during recap.

 

Considering undoing the mod as I don't like the lack of clarity at 640x480 compared to factory resolution. To each their own!

Edited by dkjones96
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Echoing @Crutch a bit, but how is everyone feeling about this mod a few years on? It seems like @Bolle did it with "satisfactory" results (dark, unfocused image; better after warm up) and @dkjones96 did it and is considering undoing it (sync loss on warm reboot and lack of clarity). I get that it's as close to Apple-endorsed as possible, but that feedback is worrisome, especially given the amount of additional tweaking both of these guys had to do.

 

It seems really hard to directly compare this to the old preferred way (Option 1 on https://powercc.org/640x480/) since there are different AB revisions and perhaps even more variation at work. I guess I could try to do it the way presented here and then fall back to Option 1 as a plan B, but it would be nice to avoid excessive rework on a 30-year-old PCB.

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Hello ttb...

 

I also use the https://powercc.org

 

I think it is one of the best sites for original Color Classics, or mods. 

 

I did the 640 X 480 mod the old time way and used option one on the above web site.  That was maybe three or four years ago.  I use my CC about two or three times a week, for maybe between one and two hours each time.  I have only had one problem develop.  About 6 months ago I found two shadows on my screen.  Apparently, the built in degassing coil on the Sony CRT was not working.  So I bought am external degassing coil and it fixed the problem ASAP.  This issue did not appear until almost three years after I did the mod.  So I believe the mod had nothing to do with it.

 

Having said that, I think Techknight's solution is the best.  But my issue is that Techknight's solution applied to only one version of the board, and Apple had made several versions of the board.  The two boards I had where not the same one that Techknight used.  So rather then screw it up, I went old school. 

 

So far, so good.

 

mraroid

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@ttb I did end up undoing it and then going with the old preferred way which is option 1 above. I kept having problems with a pair of diodes overheating an electrolytic capacitor in almost the dead center of the analog board. It runs crazy hot at 84v and stays that way even when the computer is off unless you flip the switch on the back. It does have a bit of wobble that I haven't tried to figure out yet but it isn't bad. It's much less work and way easier to reverse if you want.

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