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Color Classic VGA Mod. the CORRECT way

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So did anyone come around actually trying this and did it work?

My CC analog board is in need of a recap anyways and once it is out on my desk I thought doing one of the 640*480 mods would be a good idea.

Edited by Bolle
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So I seems I have to go second then. I just finished taking off all caps and the parts that have to be replaced for the mod and I am going to order replacement parts now.

My AB is one with part number 820-0360-B.

The parts I removed match the ones techknight had on his comparison board as well. The only strange thing is RF14 should be 243k according to the colour code but measures 237k which is closer to the 236k techknights board had.


RP8 consists of two resistors in parallel while RP23 right next to it is a single 22K one. Both seem to have been putting out a lot of heat as the board underneath is pretty dark. The heat also lifted up the pads and traces of both resistors.

I went on checking for more loose pads and found quite a few. I hope I can fix those somehow. The worst ones are those of the orange and blue wires running to the neck board.


Will report back as soon as the parts arrive and I got this thing together again.

Edited by Bolle
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Well, I guess I killed it  } :)

Spent two days recapping and applying the modifications and it seems like it did not really like it.

I started it up without the logicboard first, so I wont kill my it as well right away if something was wrong.

It does fire up, CRT seems to start but there are unnatural sounds coming from the flyback and the logic power supply can't keep up a steady 5/12V supply.

Voltages are raising to 5/12V and drop again just like there is a short somewhere, but there isn't.

I reverted to the original analog board configuration and it still does the same.

So either I fried it or I got something wrong somewhere else when recapping/repairing pads and traces.


Any ideas?

Does the CCs logic power supply produce a clean 5/12V supply without a load (say logicboard) connected?

Edited by Bolle
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Put it together to put it back into storage out of frustration and plugged it in one last time, this time with logicboard in place. Seems it does indeed need a load on the logic PSU to work. Flyback noise is gone, Mac boots, going to apply the mods again tomorrow.


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Success!  8-)


So there we go:




640 x 480 at 67Hz and 32768 colors:




This is how my board looks with the spots marked where stuff has been swapped out:





The picture has still pretty big borders on the left and right. If I turn the up the width pot it starts to form barrel distortion that can not be corrected using the pot for barrel settings.

Going to order a few 1kV caps in sizes from 1-4nF to go behind the the horizontal output transistor at CL26 to see if I can stretch the picture this way.


Techknight does your board have a cap installed there? Mine is empty in stock configuration.

Edited by Bolle
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One of the implications of fiddling with CC screens in this way is that at 640x480, text work will become difficult. The stock CC resolution is really nicely proportioned for reading, say, 10 or 12 point font in a productivity application (remember that old word processors, spreadsheets and the like just don't do zooming).


I count this one of the pleasures of using the small screens of the Compact Macs -- the screen may seem limiting, but the GUI is appropriately scaled. They are well designed for their intended use and are just nice to work on as they are. By contrast, I doubt that ordinary text will be readable on a CC screen at 640x480. Your software will need to have everything blown up to the point size of a heading.


Just putting that out there.... I think the 640x480 hack basically must ruin the machine.

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On 1/13/2017 at 4:13 PM, Bolle said:

Do you have pictures of your DVT Board?


Nope, the DVT board belonged to Haplain. I usually do his tough dog stuff. Last thing he sent me was a proto g4 logic board but I cannot fix the broken off LCD connector so its just been sitting around until I figure out a fix... 

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Good Work! Doing the upgrade on my CC analog board resulted in losing thousands of colors support.  I did this upgrade: http://colourclassicfaq.com/general/vga.html

I have a 575 Logic Board with 1mb of video memory, so I should be able to do Thousands of Colors still.  But aside from being stuck at 256 colors, it seems to work well.


If you can get yours squared away, maybe I'll consider redoing my board this way as well.  Unless someone else has a good idea of what I did wrong.

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Did you change the resistor underneath the PCB next to the opto-isolator? if not thats why. B+ is too low.

I did. What voltage should I expect for B+ and where would be a good place to measure it?


I have seen that some 550 and 575 boards have CL26 installed by default so I will probably go for that first before messing with raising B+ even more.

Loosing some brightness with CL26 installed should not be a problem for me as I can turn up the brightness right now way more than I need. Plenty of headroom there for me.

Edited by Bolle
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This is as good as it gets with 4uF on CL26 and B+ raised just a little bit.




If I raise B+ even more the height of the picture will go up as well and the pot for height is already turned down to minimum.

I will leave it this way for now and see if the HOT stays alive or if anything else fails with a few hours of usage on it.


Picture is crispy and sharp but I don't want to imagine 800*600 on this tube. 640*480 is on the edge of being bad but still useable in my eyes.

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I've done the 60hz 640x480 mod to my CC Mystic. I get the option of 800x600 56Hz and it's pretty hard on the eyes. The 56Hz refresh isn't so bad since it's such a small monitor, but the UI text looks terrible as it's finer than the pixel pitch of the CRT.

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  • 4 months later...

I have rev C.  I am thinking about doing this mod.  Did it work out for you?






While getting prepared to order parts and try out this new VGA mod I discovered the following discrepancies. I think I have a rev D board as it is labeled 820-0360-D in the bottom right corner.

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  • 2 weeks later...
I found this list of components for the analog board of a Color Classic (no version number given).
I am trying to buy diodes for my analog board.  I am not having any luck.

Reading Techknight's post - color classic mod the correct way:

He says:

DL21 and DL22 get removed and replaced with single 18V Zener at DL21. BZX85C18


Here is a list of parts (plus diodes) for the CC analog board:



The above list is from the Color Classic FAQ:



Here are the diodes listed from above:

DL5  MR10 120E
DP1  4A Bridge rectifier
DP19  U820 9250
DP22  TL431CLP
DV1  1N301 (ECG177 - Dig-Key)
DV11  Bgf (E?) 1G G1 - SMD diode
DV6  1N301

My CC analog board is part number 820-0360-C.
I don't think anyone has done the mod on a version "C" analog board.
Here are the diodes I could find on my revision "C" board:
DL-7 - near flyback
DL-8 -near flyback
Can someone tell me the difference between a DL diode and a DP diode?
Can someone point me to a part number I can use to replace the diodes above?
Still no luck finding a schematic for the analog board....  :( Most of the diodes are too small for me to make out any lettering.  How do you find the part number??

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  • 2 weeks later...

Do you have pictures of your DVT Board?

The differences between Rev D boards and my Rev B are easy to spot. Looking at the DVT board probably would help just to see if there are any obvious differences.

It is probably water under the bridge now, but I can post some photos of my Rev. C analog board if need be...



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