Installing 4K EPROMs in 2K Odyssey 2 Cartridges
I've been creating ROMs for my various electronics and solar projects. I have *a lot* of 27256 EPROMs that I desoldered off of an old phone system board. I had the board hanging up on the wall for awhile, but I finally used a small torch and removed all of the EPROMs. I wanted to have 4K available for my program, but I also wanted to put it in a cartridge that had a 2K circuit board. Additionally, I wanted to use "The Voice", which turns out needs further modifications to the 2K circuit board than you would think. The 2K circuit boards are numbered TN1018. The first modification is to cut a trace to VPP, or pin 21 of the ROM:
The second trace you have to cut is one of the fingers that normally goes to ground:
Pins 1 and 29 of the 27256 EPROM needs to be at 5+. 5+ is under pin 26. Pins 2, 26 and 27 need to go to ground. Finally, the address line A11 on pin 23 needs to be connected:
The yellow wires are ones from the large 50 pair phone cables. The insulation melts easily. I've melted two wires together before so they shorted. You have to be careful. Note that if you want to use all 8K, just connect pin 2 to the third finger from the left in the above picture. 4K is fine for my purposes for now. Let's put the cartridge back together:
That is all there is to it. Did I mention that I heart reuse? :)
--Agatha
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