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| Color Classic VGA Mod. the CORRECT way |
Posted by: techknight on 2015-11-29 06:35:36
I documented the changes to the Color Classic Analog Board to allow the board to operate at 640x480 without the transformer trace cut mod!
Here are the CORRECT changes, this allows for full width without any distortions.
CL9: Change from 3.3uF to 2.2uF 160V
CL10: Change from 3.3uF to 1.8uF 160V
DL21 and DL22 get removed and replaced with single 18V Zener at DL21. BZX85C18
RL62 Changes from 47Ohm to 100Ohm
RP61 gets 7.5K 3Watt resistor added.
J104 jumper gets removed and replaced with a 10 ohm resistor, 2 Watt.
RL70 changes from 33K to 22K.
RL54 changes from 33Ohms to 15Ohms
RP8 Changes from 15K to 33K
RP23 Changes from 22K to 33K
RF14 Changes from 236K to 216K 1% Precision resistor.
J78 moves to J79. (SMD)
RP6 changes from 4.52K to 5.11K (SMD)
I have yet to try these modifications on my CC board, HOWEVER these changes were performed on a DVT board by one of the head engineers, and the board is working properly at 640x480 without any distortions or width problems.
These were the ONLY changes found between the two boards. Also, DL21/22 does NOT overheat on the DVT board either with these changes, the changes never made it into production on the CC, but have on the LC5XX+
When i complete the restoration on the DVT board, I will post photos of a stock, and DVT. you will clearly see the changes.
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Posted by: Macdrone on 2015-11-29 07:04:36
When you do the change can you list part numbers and types please? I would love to do this but sometimes some of this needs force fed info to me.
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Posted by: uniserver on 2015-11-29 07:14:44
and again you said the 47 HZ thing is no more with this proper mod?
other wise if people just want to improve the durability of their current stock CC ab board, what would you suggest for that?
Thanks man, really great info!
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Posted by: techknight on 2015-11-29 07:20:31
This runs at 60Hz not 47Hz. Even a stock CC board with a good VRAM stick in it works with this, along with my LC575 board.
And the part numbers/types are there... The only thing I didnt list was the two 1.8/2.2uf cap types, but they are the box style film cap.
Since these mods were done by the official engineer, chances are this is a much safer and more stable way to do things than the transformer trace cut mod.
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Posted by: 360alaska on 2015-11-29 08:27:52
WOW! THANKS FOR SHARING! I have two CC's modified for VGA OUTPUT and I also have a spare analog board, I'll give er a try!
Just curious, besides all of this, do you think it would help to transfer over a 575 flyback?
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Posted by: techknight on 2015-11-29 09:30:50
the flybacks should be identical? I will have to double-check.
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Posted by: 360alaska on 2015-11-29 09:39:45
They have different part numbers so I was thinking the 575 transformer might be wound to provide a higher high voltage?
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Posted by: techknight on 2015-11-29 10:36:29
It certainly could be possible, it is a larger CRT.
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Posted by: mraroid on 2015-11-29 10:40:28
Since these mods were done by the official engineer, chances are this is a much safer and more stable way to do things than the transformer trace cut mod. Thank you for your post. I would also like to try this mod. It sounds safe...
mraroid
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Posted by: techknight on 2015-11-29 13:09:07
The vertical output IC runs a little bit warmer with this mod, make sure your fan is clean and working properly!
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Posted by: james_w on 2015-11-29 15:27:04
This is great - thanks techknight!
My CC's analogue board is sitting waiting for a recap so I can combine the two tasks 😀
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Posted by: rsolberg on 2015-11-30 10:14:30
Will this allow the display to also run at 512x384 pixels, or is that mutually exclusive to 640x480 on the sense circuitry?
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Posted by: Apache Thunder on 2015-11-30 10:43:51
I'm pretty sure the internal display was not multi-synce capable much like some of the older Mac displays at the time. The modifications made would make it run at 640x480x60hz and only that. You'd have to physically modify it again to go back.
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Posted by: techknight on 2015-11-30 11:53:52
its not multisync.
Multisync monitors require a sync processor along with a PLL to keep the horizontal circuits happy.
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Posted by: Apache Thunder on 2015-11-30 13:04:23
I suppose if you have the means you can try and add a sync processor and PLL. But would the motherboard even know how to change resolutions for the internal monitor?
Was the internal monitor on the 5xx series all-in-ones multisync capable? If so, I would guess the mystic upgrade would at least know what to do.
By the way I'm curious as to how the motherboard knows the internal monitor can do 640x480 now. Does it read voltage values from the analog board or something to determine what resolution to run at?
lol parden my ignorance with the monitor tech used in these old compacts. 😛
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Posted by: techknight on 2015-11-30 15:04:31
Nope, there are ID lines that tell the logic board what monitor is connected.
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Posted by: rsolberg on 2015-11-30 15:39:00
Thanks for clarifying the sense line thing. If one were to modify the analogue board for the higher horiz. defection voltage only, without the sense line mod, could the AB still drive the CRT at 512x384? 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.
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Posted by: olePigeon on 2015-11-30 16:46:07
rsolberg, that'd be awesome. Have 2 resolution switching. 🙂
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Posted by: gsteemso on 2015-11-30 18:17:24
It would indeed be a nifty hack, as far as that goes, but I cannot envision any circumstance where an actual user of the machine would WANT to use the lower resolution. Those machines use main memory for video, not some limiting block of separate VRAM, correct? So in theory they should be just as capable at the larger screen size, same colour depth etc. No one voluntarily sacrifices screen real-estate at those small resolutions.
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