🇦🇺 Commodore VIC-20 Internal RAM Replacement: Part 1 (First Test of 8KB) [TCE #0603]
80Thanks to PCBWAY for sponsoring this video! https://www.pcbway.com/
I've long wondered about replacing the internal 5KB of RAM in the original VIC-20 (not the CR!) in case it becomes faulty and/or to reduce power consumption. At the same time, I've wondered if it would be possible to fill in that 3KB hole in BLK0 internally. I'm just interested in the BLK0 chunk of RAM - the additional RAM upgrades get more complicated, especially if you want them to be switchable on/off without opening the VIC up ... just use a modern cartridge for those.
So far, the answer seems to be yes! It requires a bit of work removing chips ... but it reduces power draw by just over 200mA which is pretty good ... almost 20%.
My design is switchable so you can easily switch between the base 5KB or the expanded 8KB via an external switch.
I designed this board in a previous video:
• Simple KiCad For Simple Vintage Compu...
The Github for this design can be found here - in the process of being updated (12-May-2025):
https://github.com/0ddjob/Commodore_VIC20/tree/main/Internal_8KB
The method at the moment is the following:
[1] Remove the ten 2114 RAM chips from the board (UD2-UD6, UE2-UE6 on my board) ... carefully. Don't touch the single 2114 (UE1) used for the colour RAM!
[2] Remove the 74LS138 (UC4) just above the RAM chips, the RAM decoder. This will be replaced by the logic in the PLD.
[3] Install three IC sockets (turned pin preferably) in the UC4, UD4, UE4 locations: 2x18 pin and 1x16 pin.
[4] Program the PLD.
[5] Build my board and install.
[6] Install the wiring.
Done!
00:00 ... Intro
04:46 ... Old RAM removed
06:04 ... First test - YIKES!
07:58 ... Got it working with explanation
13:05 ... Close-up of final installation
14:05 ... Both RAM configs are working!
17:50 ... Channel thanks & Outro
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