TS1000 Internal RAM: Part 2

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The Clueless Engineer

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Published on October 18, 2023 10:44:28 AM ● Video Link: https://www.youtube.com/watch?v=ffY13umyZYg

Duration: 17:22

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17

Ran into some issues with the TS1000 in part 1 - the switching regulator was outputting 9V (ouch!) so I replaced it with a straight 5V input and built a new USB-to-3.5mm power cable for it.

Part 1: https://youtu.be/ELaCecWBzso

I think there may be an issue with one or more of the ULA socket connections so will investigate more.

But I pulled out another TS1000 that I had worked on a while ago. I had made the following modifications to it:
[1] Replaced all the vertical pull-up/down resistors with surface-mount MELF types
[2] Replaced the 7805 with a switching regulator
[3] Replaced all the sockets with machined pin versions
[4] The RCA socket on the original modulator broke so I installed a right-angle RCA socket - works much better IMHO
[5] Installed a simple buffer stage on the video output

Anyway, with the vLA81 and my 32KB SRAM board, it seemed to work! It would be the same in a ZX81.

Certainly it seems that 16KB mode is working fine ... I've never been able to work out 32KB mode ... maybe it's working ... maybe not ... ?

Some RAM size tests that can be done:
https://www.vintage-radio.net/forum/showthread.php?t=120165

I will try to load some software next.

My RAM board:
https://github.com/0ddjob/ZX81/tree/main/RAM_Upgrade

Another design with surface mount SRAM:
https://github.com/redhawk668/ZX81-Internal-16K-Expansion

vLA81 modern ULA replacement:
https://www.vretrodesign.com/products/vla81-zx81-ula-replacement