The Macintosh Colo(u)r Classic has a built-in screen resolution of 512x384 pixels, with a somewhat hidden option to get 560x384 pixels in a pinch. As many, many people have noticed, well, this isn't much screen real estate. Most games made since about 1994 or so require 640x480 as a minimum, and even if you're not playing games, a little extra screen (or, in this case, about 45 percent more) never really hurts anything. This upgrade was developed with that in mind.

I would be remiss if I failed to give credit to the Japanese "entity" known as "Takky" for developing the original tune-up method. Credit is also due to Stuart Bell and his Colo(u)r Classic Forum, Mr S. Watanabe (aka MISUTHiKU), and Eric Neumann, whose translation of the original modification from Japanese to English was instrumental in knowing what went where. If you don't know where to start with this modification or are at all unsure about how to disassemble a CC, I highly recommend you read through Eric's site first. He has several excellent photographs and directions for disassembly which I see no need to repeat here.

This is, to the best of my knowledge, the first time that the details of this particular VGA modification (not the 13" or "High-Res" modification) have been performed. As such, I respectfully request that if you refer to or link to this method elsewhere, I, Chris Lawson, receive credit for it. I won't be so audacious as to name the modification; I'm sure it will take on a life of its own once the rest of the Colour Classic community picks up on it.

PLEASE NOTE: if you perform a VGA modification to your Colour Classic's analogue board, you MUST use a logic board other than the stock Colour Classic logic board. The CC board will not put out a VGA signal and will be unable to drive the monitor, resulting in what will appear to you as a dead CC. And, of course, I take no responsibility for anything you might do to your Mac or yourself while attempting this modification.

OK, all right already, I'll get to the modification :)

Step 1: Power Pin Isolation

Pin 8 isolated

Pin 8 (to the left of pin 7, which is clearly marked, if the numbers are upside-down) on the power transformer of the CC analogue board must be isolated from the rest of the board. This is most easily accomplished with a Dremel-type rotary tool and an abrasive cutoff wheel (not the fiber composite wheel) at low speed (under 3000 RPM). See Figure 1 at left for a close-up of what the board should look like when you're done isolating the pin. Note the copper colour in the photograph around pin 8. This is a fault of the camera and lighting; in actuality the white composite material of the circuit board can be seen in this space. You should NOT be able to see any copper underneath where you have cut with the Dremel; if you can, cut away the copper until you see white composite board. Be careful NOT to cut through the entire board; a steady and gentle hand with the Dremel is a very important element of a successful conversion. A caveat: if you use a meter to determine whether or not you have successfully isolated pin 8, you'll never figure it out. Even with pin 8 successfully isolated, my continuity tester registered a connection between pins 8 and 9. I believe this is probably due to a connection elsewhere in the circuity of the board, as I made doubly sure by inspection that the printed conductor had been fully severed.

Figure 1: photograph of underside of analogue board around ZP1 with pin 8 isolated.

Step 2: Voltage Conversion

Jumper on pins 8 and 12

This is the key difference between the VGA modification and the so-called "High-Res" modification. The voltage added to pin 8 is 68.4 volts (give or take a small margin) in this modification, while in the so-called "High-Res" modification, it is 80 volts. This higher voltage puts extra stress on the various components of the analogue board, and as anyone who has ever tried to find a CC analogue board knows, they are exceedingly rare and expensive. Personally, I'd like to make every effort to preserve my boards as long as possible, so I highly recommend the VGA modification over the "High-Res" modification.

To put the proper horizontal deflecting voltage onto pin 8, you must solder a jumper from pin 8 to pin 12 (also clearly marked; see photo above for) on the same transformer. Make sure to use insulated wire that is sufficient for carrying a fairly large current; anything with a conductor about the thickness of the power transformer's pins will be sufficient. A photograph of my converted board is shown to the right in Figure 2.

Figure 2: photograph of underside of analogue board around ZP1 with jumper installed on pins 8 and 12.

Step 3: Sense Wire Modification

This step is where my procedure differs from those published elsewhere on various Japanese sites, mostly by members of the Club for Creating the Strongest Color Classic (CCSCC). The other modifications suggest one of two options: either modify the (usually) LC575 logic board or fool around with wires in the wiring harness. Doing the logic board modification has no advantage that I can see; in fact, I recommend against it because, should you ever have occasion to replace the logic board, you will need to modify the new one as well. Likewise, I recommend against cutting and patching wires in the wiring harness simply because if you make a mistake, it's very difficult to splice wires in an IDC cable (and even more difficult to re-wire one). Due to the major disadvantages of the previously available methods, I decided to come up with one that contained all the modifications on the analogue board where they could be relatively easily undone. A/B connector, modified

To allow the reader to better understand the details of this modification, I offer this short explanation of sense coding. Macintosh computers detect the type of monitor attached to them by three wires in the monitor connector. These lines are called "sense lines" and are labelled S0, S1, and S2. In the case of an ordinary 12" RGB monitor, to which the CC analogue board is akin by default, S1 is left disconnected, while S0 and S2 are connected to ground. A VGA monitor requires S0 and S1 to be connected to each other, while S2 is left disconnected.

In order to change the sense lines to those of a VGA monitor, you must first remove the jumper at J78 in order to isolate pin 20. If you don't have J78, simply cut the connection from pin 20 to the analogue board connector at either of the red arrows in Figure 4 (courtesy of Eric Neumann) below. Once pin 20 has been isolated, you must solder a wire jumper from pin 20 to pin 24 on the analogue board connector, and disconnect (isolate) pin 25 with the Dremel. See Figure 3 to the left for a properly configured board. Space is very tight in this area, so be EXTREMELY careful with the Dremel. If you want, you could probably use a very thin metal file to isolate the pin instead.
Figure 3: photograph of modified analogue board around connector.

A/B without J78/J79
Figure 4: photograph of analogue board lacking J78/J79 around connector.

Step 4: Video Adjustment

For this step, I again refer the reader back to Eric Neumann's site, where he explains how to adjust the video controls in the back of the analogue board for a proper display. Another note: you can use INSULATED metal tools to do these adjustments; the potentiometers you'll be adjusting are all plastic and not ferrite-cored (and thus not metal-sensitive). If you have plastic adjustment tools, by all means, use them.

That's it! You're done! Go celebrate! Have a beer — you'll need it after this :)

Copyright 2001-2 by Chris Lawson. All rights reserved.
Last modified on 14 Aug 2001
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