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Color Classic VGA Mod. the CORRECT way


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I'm contemplating the viability of making the sense lines switchable in order to allow use of the stock CC board and lower resolution in a VGA modified CC.

Now, I have heard that a 575 AB can drive the CC monitor at 800x600, so one wonders if that would also be possible with these mods.

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No, I didnt do any cross-referencing to modern part numbers. I just grabbed the values and voltages of everything before shipping the board back out. 

 

The only thing that you have to get right is the two capacitors I listed at the top. They are the box style. Mylar film I believe. Everything else is garden variety. 

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OK, finally found the details on the 575 analog board in a CC.
 

This analog board comes from Apple configured at 640x480 66Hz. The "Hi-Res" mod or "VGA Mod" are *not* required, and will probably kill your 575 board. However, the sense line coding issues are still the same ...

I set my monitor sense line to "VGA" which gives me several working resolution choices: 640x480x66Hz, 640x480x60Hz, 800x600x60Hz, and 800x600x56Hz. ... 800x600 is nice and usable, though the dot pitch is a little grainy.

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Note that this mod requires physical modification to both the 575 AB and the CC inner framework to get the board to fit.  Given that, it's probably better to do the "correct" VGA mod on an original CC AB, unless you are absolutely determined to get to 800x600 on the original CRT, or don't care about sawing up the CCs internals (which is required for some motherboard mods anyway).

People who know more about this than me:  what are the chances you could get the same result using a "correctly" modified CC AB, with sense line ID set for VGA?  I seem to recall someone here who did a MiniITX CC did just that.

Other caveats and gotchas at the link:
 

Live: http://www.fenestrated.net/~macman/CC575/

Archive: http://web.archive.org/web/20141113164633/http://www.fenestrated.net/~macman/CC575/

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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. I'm not sure I should attempt this now since there could be more differences between my board and the DVT board that weren't noted.

 

RP61 – Already populated with 7.5 K resistor

J104 – Couldn't find - suspect it is populated and has an R-designator?

RL54 – Has 18Ohm resistor in place not 33Ohm

RP8 – Already 33K resistor

RP23 – Empty

RF14 – Populated with 243K resistor

RP6 – Populated with 5.6K resistor

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Any resolution to your problem avadondragon?  I am about to place a order with Mouser...

 

Also, what did we decide re the flyback transformer?  Is the one on a 575 more robust?   Anyone have a source for new flyback transformers for the CC or 575 board?

 

jack

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techknight....
 
I am thinking of doing this mod to a CC analog board.  If I did this mod, I would probably roll in a logic board from a 575. 
 
If I did that, would I still need to do the sensing mod with RezEdit to the 575 logic board?  Or could I just slide the 575 logic board in after this analog board upgrade?
 
One last question...  My CC analog board work fine.  But DL21 and DL22 look dark and old.  I was thinking about replacing them.  However, I can not read the values on the diodes.  Do you know the values?
 
Thanks.
 
jack
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Nope. once the analog board is modded, the logic board will see it as a 640x480 system as a true 575 would. 

 

the DL21/22 thing is very common on those boards. 

 

In order to keep the sweep in the 512x384 margins, they had to clamp down one of the V supplies, and thats what those Zener diodes do. 

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Techknight....

 

Thanks.

 

Looking at your mod more closely, I read:

"DL21 and DL22 get removed and replaced with single 18V Zener at DL21. BZX85C18."
 
That should do the trick?
 
You also posted this:

"The vertical output IC runs a little bit warmer with this mod."
 
I looked at this parts list but could not find the vertical output IC part number:

http://colourclassicfaq.com/tech/ccparts.html
 
So I took my Color Classic apart to check.  The vertical output IC is in the metal cage next to the flyback,  It is the IC to the left of the big gray cable.  It has a small clip (heat sinc?) over it and it is bonded to the metal cage - i guess for better heat dispersal. photo enclosed.
 
Unfortunately, the IC was too old and I could not make out any lettering on it.  Do we know the part number of that IC? 
 
I thought I would look up the equivalent but with a higher temperature rating.
 
I am about to order a bag of parts for this mod from Mouser.  Can you think of anything else I should swap out as log as I am into this?
 
Thanks for posting all of this information.
 
jack
 

 

post-4137-0-76819600-1462138571_thumb.jpg

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I forget which IC it is, but I think its a TDA brand IC. You dont really need to change the IC, you just need something to dissipate the heat. However, it wouldn't really be any different if you did the transformer trace cut mod, the IC would see the same load and same specs. 

 

at this point I would leave the vertical IC alone, and just watch it closely afterwords. If the picture starts to shrink and fold over as its running, youll need to heatsink it somehow. or FAN. 

Edited by techknight
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