Dragon 32 Ram Upgrade to 64K

TheCorfiot

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Hi Forum Chums
Time for a spot of retropr0n :D

I was commissioned by Paradroid90 to repair and upgrade this poor abused Dragon 32.

The Main fault was a short circuit 4.7microfarad Tantalum Capacitor on the +12V Rail (C10) which was smoking the good ole Blue stuff. Simply replaced this with a 4.7 polarised Electrolytic.
Also one of the 4116 DRAMS (IC1) was failing as there was chunks of garbage on the screen but the system responded.


I replaced the 16x 4116 DRAMS with 8x4164 64K DRAMS with 128 cycle refresh, this point is important as the dragon uses the 6809E's std refresh circuit which cannot handle modern 256 cycle refresh DRAMS.

The 4116 DRAMS require 3 separate DC Voltages to operate, +5, +12 and -5, whereas the 4164 only requires +5V albeit on Pin 8 which the 4116 has +12V...What a kerfuffle.

Some careful trace cutting of Bank zero rails and reallocation, including lots of continuity testing lol.. proved fruitful.
Finally the RAS1 line which drives Bank1 which is no longer fitted is rerouted to A7 of the new 4164 chips.

One last mod is needed to tell the Dragon it now has 64K of RAM and that is to change the signal of bit2 of #FF22.
This is achieved by removing R73 and connecting Pin 12 of IC35, the 6821PIA, to ground.

We now have a Dragon32 configured identically to the Dragon64 regarding Memory capacity and paging support.
Apart from being unable to offer 48K Basic Mode a la Dragon64 this Dragon32 can now boot OS9 and Flex and most Dragon64 Programs.

Enjoy the piccys

TC :)
 

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Sardine

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wow!!!


just ,, wow!!

my dragon 64 just got its nose bent :) I knew this was possible but damn!!! complicated, congrats,,

(goes off to see what the heck OS9 & Flex is,,,,,,,,,)
 

Paradroid90

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Wow thanks Bas :) Did not realise how much work was involved my friend ........As always work and skill holds no bounds and it will be cool to have such a unique Dragon 32 :)

Demon Attack and OS9 here I come :) .......... Well done and thanks again :)
 

Sardine

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Skill !!!!! Yes..

So,, you now have NO EXCUSE not to make an RGB mod for my dragon .

(cracks whip!!)

:D
 

protek

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Awesome work, my friend! (y) You truly are an inspiration to us all!
 
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